In this blog, I’ll be exploring subjects of general interest/concern to me and wider society:
In this blog, I’ll be exploring subjects of general interest/concern to me and wider society:
Now I make known to you, brethren, the gospel which I preached to you, which also you received, in which also you stand, by which also you are saved, if you hold fast the word which I preached to you, unless you believed in vain.
For I delivered to you as of first importance what I also received, that Christ died for our sins according to the Scriptures, and that He was buried, and that He was raised on the third day according to the Scriptures, and that He appeared to Cephas, then to the twelve. After that He appeared to more than five hundred brethren at one time, most of whom remain until now, but some have fallen asleep; then He appeared to James, then to all the apostles; and last of all, as to one untimely born, He appeared to me also. For I am the least of the apostles, and not fit to be called an apostle, because I persecuted the church of God. But by the grace of God I am what I am, and His grace toward me did not prove vain; but I labored even more than all of them, yet not I, but the grace of God with me. Whether then it was I or they, so we preach and so you believed.
1 Corinthians 15:1-11
Today we are fortunate to have many excellent translations of the Holy Bible in English. The highly accurate New American Standard Bible (NASB) offers its readers great ways to enrich their knowledge of the inspired word of God, with a number of unique scholarly features that highlight the challenges of translation from the original tongues, as well as revealing how the New Testament comes alive when viewed through the lens of the Old Testament.
Tune in soon to find out more………………….
Scientists love to tell stories about the quest to understand the universe-stories that often have profound implications for belief or disbelief in God. These accounts make their way into science textbooks and popular culture. But more often than not, the stories are nothing but myths. Unbelievable explodes seven of the most popular and pernicious myths about science and religion. Michael Newton Keas, a historian of science, lays out the facts to show how far the conventional wisdom departs from reality. He also shows how these myths have proliferated over the past four centuries and exert so much influence today. The seven myths, Keas shows, amount to little more than religion bashing-and especially Christianity bashing. Unbelievable reveals: Why the vastness of the universe does not deal a blow to religious belief in human significance. Why the “”Dark Ages”” never happened. Why “”Flat Earthers”” had basically disappeared by the third century B.C. Why the real story of Giordano Bruno’s life and death is far more complicated than the popular account of him as a martyr for science. What everyone gets wrong about Galileo, and why it matters today. Why the notion that Copernicus “”demoted”” humans from the center of the universe didn’t gain traction until centuries after his death. The futuristic myth that scientists and others are positioning to challenge religion. In debunking these myths, Keas shows that the real history is far more interesting than the common account of religion at war with science. This accessible and entertaining book lays out powerful arguments that will be embraced by religious believers tired of being portrayed as anti-intellectual and anti-science.
“Unbelievable should be on the shelf of every science popularizer and college astronomy professor. Perhaps then we can begin to purge our culture of the ‘science is the enemy of religion’ myths Michael Keas slays in his refreshingly contrarian book.”
–Guillermo Gonzalez, Assistant Professor of Astronomy, Ball State University; coauthor of The Privileged Planet
“Not content to knock down the myths about the alleged conflict between science and religion, Mike Keas shows where they came from and how science popularizers like Carl Sagan have used them to further their own agendas. Using a wide range of sources, including textbooks and television shows, Keas explains how these myths got into the bloodstream of our culture. An invaluable resource.”
–James Hannam, author of God’s Philosophers and The Genesis of Science
“Michael Keas decisively debunks an array of myths that have long impeded our understanding of the histories of science and of religion. Unbelievable may earn Keas plenty of enemies, but nobody concerned with real evidence can dismiss his argument out of hand. This is a brilliant, engaging, and important contribution to a debate about truly universal matters.”
–Dennis Danielson, Professor Emeritus, University of British Columbia; editor of The Book of the Cosmos
“Michael Keas does a splendid job dispelling viral myths and common errors about the relationship between science and Christianity. This book is well documented and written in a pleasing style accessible to the general reader as well as scholars.”
–Jeffrey Burton Russell, Professor of History Emeritus, University of California, Santa Barbara; author of Inventing the Flat Earth
“The notion of inevitable, perpetual conflict between science and religion is one of the most prevalent grand narratives in the modern West. It takes many specific forms, and Michael Keas deftly disposes of myths like these with lively, thoroughly researched stories that will leave readers much better informed.”
–Edward B. Davis, coeditor of The Works of Robert Boyle
“The supposed warfare between science and Christianity has long been a staple of science textbooks and popular science. Michael Keas skewers the most popular myths used to illustrate that warfare, displaying his deep knowledge of the history of science. If you want to understand the true, and positive, relationship between science and Christianity, you should read Unbelievable.”
–Jay W. Richards, bestselling author of Infiltrated and Indivisible
On that day I raised My hand in an oath to them, to bring them out of the land of Egypt into a land that I had searched out for them, ‘flowing with milk and honey,’ the glory of all lands.
Any unbiased reading of the Bible will soon reveal that the Creator of the Universe has had a long and enduring relationship with the Jews. This people group were the first humans to forge a relationship with God, where He made Himself known to them and guided their founding of a nation in a relatively tiny strip of land on the eastern shores of the Mediterranean Sea. The Biblical narrative accurately portrays much of the history of the ancient Jewish nation and modern archaeological research is unveiling more and more details that affirm the historicity of their story, despite militant opposition from secular academics who have been proven wrong time and time again.
Because of their unfaithfulness to their God, the former glory of the kingdom established by David and his son, Solomon, was gradually but inexorably wrenched from them because of their reluctance to follow the laws and statutes laid down for them in the Law of Moses, as well as their eagerness to follow after the false gods of the surrounding nations and the inter-marriage of their nobles with the nobility of foreign cultures(and against God’s wishes). As a result, ancient Israel and Judah suffered many waves of conquests by foreign imperial powers including Assyria, Babylon, Persia, Greece, Rome, Byzantium and the various waves of Islamic invasions over the centuries and millennia. Israel ceased to be a free nation about 2,600 years ago being occupied by foreign powers throughout much of this time.
Throughout this time, the Jewish people have suffered terrible persecutions under various powers, culminating with the attempt of the evil Nazi regime to exterminate them from the face of the Earth. Still, despite these perils, they have bucked all the odds to maintain their culture and religion; indeed they are the only truy ancient people that exist through modern times. After World War II, the United Nations created a homeland for the remaining Jews, which culminated in the declaration of independence of the modern state of Israel on May 14 1948. The declaration was immediately condemned by all the nations surrounding it. Thus Israel had to work hard from the outset to establish its borders, rapidly developing an excellent military machine that staved off aggressive behaviour by its surrounding enemies, and which remains so to this day.
In the 70 years since its founding days, the story of Israel has been one of astonishing prosperity, so much so that many Bible believing Christians accept it as a clear and unambiguous miracle in our times. Furthermore, it is clear that while the majority of contemporary Jews do not accept Jesus as their Messiah, the Lord would not make a complete end of them, but established them again for the sake of a minority who have(or will) come to accept Christ as their Lord and Saviour. Furthermore, the Bible foretells that Israel will play an important role in converting many unbelievers to the true God during the Great Tribulation period.
Most denominational Christians however, have been taught the false doctrine of replacement theology, where the modern Church has taken the place of Israel, and as a result, know very little about how Israel will play a central role in God’s ultimate plan for the salvation of many people. This was essentially my thinking for most of my life, as I continued in my walk with the Catholic Church, being largely ignorant of Biblical knowledge. But it is equally true of many Protestant denominations, which teach nothing concerning the true role of Israel in God’s redemptive plan for humankind. Only when I began to read the Bible for myself, as a non-denominational Christian, that I rejected the Catholic position of replacement theology. With the Lord, there is the Church and then there’s Israel; they are not one and the same. With Israel, it’s personal.
Consider the particular interest our Lord has expressed in the land of Israel;
For the land you are going in to possess is not like the land of Egypt from which you came. There you planted your seed and watered it by foot, like a vegetable garden. But the land you are crossing over to possess is a land of hills and valleys, drinking from the rain of the heavens it drinks in water. It is a land that Adonai your God cares for—the eyes of Adonai your God are always on it, from the beginning of the year up to the end of the year.
The prophet Ezekiel writes:
Therefore say to the house of Israel: Thus says the Lord God: Not for your sake do I act, house of Israel, but for the sake of my holy name, which you desecrated among the nations to which you came.
So what’s it all about then? In a phrase, the execution of Absolute power!
The prophet Jeremiah writes:
Thus says the Lord, “If My covenant for day and night stand not, and the fixed patterns of heaven and earth I have not established, then I would reject the descendants of Jacob and David My servant, not taking from his descendants rulers over the descendants of Abraham, Isaac and Jacob. But I will restore their fortunes and will have mercy on them.’”
Jeremiah 33: 25-26
In other words, the Lord would sooner abolish the laws of nature than renege on his promises to Israel.
So let’s take a closer look at the remarkable rise of Israel in the modern psyche. As a nation state, Israel is tiny, with a land area of just 21,000 square kilometres, smaller than Wales and ranking about 150th out of the 200 or so nations on Earth. It’s population is currently 9 million, of which 75 per cent identify as Jew. The Gross Domestic Product (GDP) of Israel reflects a different picture however; $360 billion, ranking it as the 54th richest nation in the world. Its per capita annual income is even more impressive though, at $42,000 per annum, making its citizens the 25th richest nation in the world; almost as rich as the average UK dweller. The life expectancy of the average Israeli is 82 years, where it poles as the 8th longest among the other nations of the world. Israel’s age demographic though is astonishing and contrary to every other developed nation currently in existence. 25 per cent of the population are under the age of 14 and 40 per cent are aged 25 years and younger. Only 11 per cent of the Israeli population is aged 65 years and older!
This very youthful population is also highly educated; 45 per cent of Israeli’s hold a Bachelor’s degree or its equivalent; higher per capita than any other nation on Earth. Their official language is Hebrew, for centuries considered an all but dead language, but thanks to the efforts of Jewish linguists, is now widely spoken and thriving. Curiously, though Israel is one of the most technologically advanced nations currently in existence, her citizens are taught little or nothing about Darwinian evolution in public schools, which dovetails with the ideology’s current rapid decline as a proper scientific theory of origins. And yet, Israel is a shining light in the emerging biotechnological and agricultural industries, both of which require an excellent knowledge of the life sciences.
Because of more or less incessant terrorist threats from foreign regimes, Israel has one of the best trained professional armies in the world. The so-called Israeli Defence Forces (IDF) has about 150,000 full-time members and over 400,000 reserves. All Israeli citizens over the age of 18 are obliged to undergo two years and eight months of military service for men and two years for women, although many seek exemptions on religious, pyschological and physical grounds.This rise in military power also comports with the Biblical narrative, which describes the desolate land of Israel being revived from a “valley of dry bones”(see Ezekiel 37):
So I prophesied as He commanded me, and the breath came into them, and they came to life and stood on their feet, an exceedingly great army.
Despite more than half of the land being desert and only 20 per cent being arable, Israel is a world leader in irrigation technology. The north of the country receives a plentiful supply of rain but the south is much more arid, with the result that water transport and use is carefully regulated. The statistics are impressive; agriculture’s share of total water use fell from more than 70% in 1980 to 57% by 2005, and is projected to drop to just 52% by 2025, according to a recent report. Many nations around the world have benefitted greatly from Israel’s lead in this regard. Indeed this small nation has become the fruit basket of Europe and the Middle East, growing and exporting over 40 different types of fruit. Indeed, 95 per cent of all Israel’s food is homegrown, supplemented by imports of meat, grains, coffee, cocoa and sugar. Israel also produces most of the flowers sold in Europe(especially during the winter months), with an industry estimated to be worth $60 million. These flowers are almost exclusively grown on 214 hectares of land.
Just as the Bible informs us, Israel has truly become “a land of milk and honey.” Specially bred, disease-resistant cows produce the highest amounts of milk per animal in the world, with an average of 10,208 kilograms of dairy in 2009, according to data published in 2011 by the Israeli Central Bureau of Statistics, outperforming cows in the US (9,331 kg per cow), Japan (7,497), the European Union (6,139) and Australia (5,601). Honey production in Israel is prodigious, with more than 100,000 apiaries scattered across the country and exported to many other nations around the world. And despite the alarming decline in bee numbers in almost every other country, Israel’s bee populations have not endured such decimation, thanks to the implementation of a number of ingenious management strategies. Indeed, the Israeli department of agriculture estimate that the value of their bees as vehicles of pollination is worth more than 30 times the value of the honey they produce! In 1948, only about 400,000 acres of land in Israel could be tilled. Today it stands at over a million acres, with productivity increasing by a factor of 16 per unit of water used. And instead of growing strains of wheat that are waist high, as is the case in most other nations, Israeli farmers cultivate new varieties that only grow to knee height and so require far less water to bring them to maturity.
In the spheres of technology, Israel ranks as the 8th most powerful nation in the world. Outside of Silicon Valley, California, Silcon Wadi on the coastal plains just outside Tel Aviv has the highest number(over 3,000 as of 2019) of IT start-up companies in the world. The first anti-virus software was formulated here, as was the first voicemail technology, and all manner of memory sticks that we use in our everyday lives. Motorola, Microsoft, Celebrite and Intel all have major investments here. The oil industry is booming at an unprecedented rate in Israel with valuable oil and natural gas reserves found in the Negev, the Golan Heights and most recently off shore in the Leviathan and Tamar fields. Analysts suggest that the energy reserves in these newly discovered sites could power the nation for another 300 years! What’s more, it is expected that Israel will become the major supplier of petrochemicals to the European nations by building under-sea pipelines across the Mediterranean.
Israel is now also active in the exploration of space, successfully launching the cheapest ever lunar probe named Beresheet(Hebrew for “In the beginning”) which attempted a soft landing on the dusty plains of Mare Serenitatis on April 11 2019 but which proved unsuccessful in the end. Despite the setback, much new science was still achieved and they will certainly try again in the near future.
By most anyone’s standards, the story of the re-birth of Israel is a remarkable phenomenon. Look how much they have achieved in only one human generation! But all of this was foretold in the prophecies of Ezekiel, most likely dated to 7th century BC:
Thus says the Lord God, “On the day that I cleanse you from all your iniquities, I will cause the cities to be inhabited, and the waste places will be rebuilt. The desolate land will be cultivated instead of being a desolation in the sight of everyone who passes by. They will say, ‘This desolate land has become like the garden of Eden; and the waste, desolate and ruined cities are fortified and inhabited.’ Then the nations that are left round about you will know that I, the Lord, have rebuilt the ruined places and planted that which was desolate; I, the Lord, have spoken and will do it.”
And yet, the Biblical narrative also suggests that this new-found prosperity will attract the eyes of power-hungry nations surrounding it, like a proverbial moth to a brightly lit lamp:
After many days you will be summoned; in the latter years you will come into the land that is restored from the sword, whose inhabitants have been gathered from many nations to the mountains of Israel which had been a continual waste; but its people were brought out from the nations, and they are living securely, all of them. You will go up, you will come like a storm; you will be like a cloud covering the land, you and all your troops, and many peoples with you.”
‘Thus says the Lord God, “It will come about on that day, that thoughts will come into your mind and you will devise an evil plan, and you will say, ‘I will go up against the land of unwalled villages. I will go against those who are at rest, that live securely, all of them living without walls and having no bars or gates, to capture spoil and to seize plunder, to turn your hand against the waste places which are now inhabited, and against the people who are gathered from the nations, who have acquired cattle and goods, who live at the center of the world.’ Sheba and Dedan and the merchants of Tarshish with all its villages will say to you, ‘Have you come to capture spoil? Have you assembled your company to seize plunder, to carry away silver and gold, to take away cattle and goods, to capture great spoil?’”’
The Bible also asserts that Israel is the centre of the world as God sees things:
Thus says the Lord God, ‘This is Jerusalem; I have set her at the center of the nations, with lands around her.
And when we look at Israel’s geographic location, it indeed lies at the hub of three continents; Africa, Europe and Asia.
The Bible also confifdently predicts that Israel will always attract trouble makers and that eventually all the nations will be gathered against it under the leadership of the Anti-Christ:
It will come about in that day that I will make Jerusalem a heavy stone for all the peoples; all who lift it will be severely injured. And all the nations of the earth will be gathered against it.
Already, we can see this gradual build-up (a Biblical “hook in the jaw”) with the hatred expressed by the politicians of many countries toward Israel as well as pervasive anti-semitism(a global phenomenon). Sadly, one of Israel’s greatest enemies is the United Nations(UN). For example, Syria bombs its civilians with chlorine gas, China tortures dissidents, Venezuela restricts access to food, and Burma is engaged in the ethnic cleansing of its Muslim minority. Yet despite these attrocities, the UN Human Rights Council trains the bulk of its outrage on, you’ve guessed it, Israel!
At the time of writing, 31 UN members don’t recognise the state of Israel. Additionally, the nations of Bolivia, Mali, Mauritania, Niger, Qatar and Venezuela have suspended ties to Israel. Most of these nations do not want the state of Israel to exist. There are also several countries, most notably Egypt, that recognise the state but almost always vote against it. That is how far-reaching the Israeli-Palestinian conflict has become!
The UN has chosen to oppose Israel at nearly every turn because of the influence and encouragement of all of these member states. On the UN security council, Israel has the support of the U.S’s power of veto and is therefore safe from most harmful resolutions, but in the general assembly the anti-Israel countries almost always win out. The most recent example of this was the decision to condemn the United States for recognising Jerusalem as Israel’s capital even though they have every right to claim it as their own. That resolution overwhelmingly passed. But if the UN were nicer to Israel, every Muslim majority country in the world (except Albania and a few others) would withdraw from the organisation and thus would lose all of its influence over the Muslim world. There would be no more peacekeepers in Syria and Iraq, no nuclear weapons inspectors in Iran, etc. To my mind, the UN has strategically chosen to alienate Israel, over dozens of others. As a result, most Israelis are suspcious of the UN to the extent that it is a miracle that they haven’t yet severed all ties with the organisation.
Yet it is important to remember that both the UN and the state of Israel were both founded on very similar principles: the exercise of democracy, liberty, national self-determination, as well as freedom from persecution and the respect for basic human rights. But the simple truth is that the vast majority of countries that oppose Israel respect none of these principles, as their actions so clearly demonstrate. Moreover, most of them don’t even care for an independent Palestine either. They just view Israel as a convenient scapegoat. It is tragically ironic that the UN, an organisation that has done so much good for the world, is siding with tyrannical regimes rather than a nation that clearly shares its own values!
Still, Israel is here to stay no matter what evil intentions the nations plot against her. Jesus Christ ascended into heaven from the Mount of Olives in Jerusalem and the Bible tells us that He will once again set foot on it at his second coming, where He will fight against those nations wishing to destroy Israel:
Then the Lord will go forth and fight against those nations, as when He fights on a day of battle. In that day His feet will stand on the Mount of Olives, which is in front of Jerusalem on the east; and the Mount of Olives will be split in its middle from east to west by a very large valley, so that half of the mountain will move toward the north and the other half toward the south.
So, we’re living in exciting times, times that most unbelievers are completely oblivious to; but that too was foretold.
All we can do is take the advice Christ Himself left us;
Therefore, be on the alert—for you do not know when the master of the house is coming, whether in the evening, at midnight, or when the rooster crows, or in the morning— in case he should come suddenly and find you asleep. What I say to you I say to all, ‘Be on the alert!’”
Neil English is the author of a large historical work; Chronicling the Golden Age of Astronomy.
The Spring sky offers many delightful sights for the backyard observer. While the nights are shorter, the temperatures are generally milder and more conducive to observing for prolonged lengths of time. In this project I have selected what I have come to discover is a first-rate grab ‘n’ go telescope(which can be tested!!!); a customised 130mm f/5 Newtonian reflector. It has a very well-figured SkyWatcher primary mirror with state-of-the-art and durable high reflectivity coatings, an upgraded secondary mirror(with the same high reflectivity coatings) with a modest 26.9 per cent central obstruction. The tube is lined with cork and overlaid with flocking material to provide excellent contrast and good thermal stability, ideally suited to high resolution work. The primary and secondary mirrors have easy to adjust hand screws to achieve ultra-precise collimation in seconds. It cools very quickly, and provides gorgeous, high-contrast images at magnifications from 26x to over 500x when conditions allow. It proved very cost-effective too; typically a small fraction of what I had already spent on similarly sized telescopes in the past. The instrument sits stably on my Vixen Porta II alt-azimuth mount, equipped with slow motion controls on both axes, and which allows me to move the telescope very smoothly and precisely, even at ultra-high powers. I can lift the telescope and tripod with one hand and whisk it into the garden where I let it acclimate for about 20 to 30 minutes (the latter if high resolution targets are being imaged) prior to use.
This choice of grab ‘n’ go didn’t come naturally though. For a decade, I was caught up in the pretentious and materialistic world of tiny, high-quality refractors costing an arm and a leg. Yes, I’ve had my fair share of ‘poodles’;
A Televue 76,
A 90mm ED
And a few other smaller 60-63mm apochromats to boot.
Only through extensive field experience did I learn that they all had their limitations. The 3- and 4 inch refractors ran out of light too quickly and didn’t have enough resolving power for my particular interest in close double stars. And while the 5-inch refractors certainly delivered more light and better resolving power, I quickly grew tired of adjusting their pivot points on a large and heavy mount on the fly, and straining to attain a comfortable observing position whilst observing objects at high altitudes.
Above all else, I learned that if you’re not comfortable observing, you won’t stick at it for very long!
Enter the modified 130mm f/5, pictured above. Its lighweight, quick cool down time and with optical performance more closely aligned with a 5-inch than a 4-inch refractor, quickly won my admiration. It was another one of those sweet experiences one ocassionally stumbles upon in life. I just found it hard to fault.
But it was the sheer ease of use, the comfortable positioning of my body in all sky orientations, that finally convinced me to give up on similar sized refractors. Nowadays, the largest refractor I have any interest in is a humble 80mm f/5 achromat; the subject of my next book. Furthermore, the fact that none of my former associates (mostly refractor nuts and “fair weathered” friends, who turned on me because I refused to become a “poodle pusher”), were willing to test and publicly report just how good a 130mm f/5 Newtonian could be, revealed to me all too loud and clear that they were in denial about its capabilities. Their reticence all too easily demonstrated the true level of their experience; which didn’t amount to very much, in retrospect!
Sorry to burst your hideous bubble boys, but you’re just not credible!
In this article, I want to share with you some of the wonderful sights that grace the vernal heavens and which are accessible to an amateur equipped with a 4- or 5-inch telescope. The observations I will report are from a fairly dark, rural sky, which enjoys excellent transparency, owing to the frequent weather systems that sweep up particulates very effectively, as they move in off the Irish Sea. What’s more, they are fairly easy to find and are a joy to study from the comfort of my back garden.
Object 1: Messier 3
Let’s begin our journey with a visit to Messier 3, a bright(magnitude +6) globular cluster on the border between Bootes and Canes Venatici. To find it, imagine an invisible line between the bright orange star Arcturus and Cor Caroli(itself a rather fetching double star for small telescopes). Almost exactly half way between these stars, binoculars will pick up a fuzzy star about half the size of the full Moon in an otherwise unremarkable patch of sky. Keen eyed individuals from the darkest sites will likely detect it with their eyes, but so far it has eluded this author’s visual acuity.
Charged with a power of 87x (Parks Gold 7.5mm), M 3 is an arresting sight, with a bright, rather condensed core surrounded by a distinctly more ragged periphery. If conditions permit, crank up the power to 135x(an old 4.8mm T1 Nagler) and you will be able to resolve quite a few of its outlying stars. Indeed, I find that more stellar members can be seen in M 3 than in the more celebrated M 13, even though the latter is brighter and slightly larger. Averted vision will help you see many more stellar members. Spare a thought for the prodigious distance of M 3; 27,000 light years from the solar system. At this distance, this magnificent bauble of starlight spans a diameter of about 180 light years, inside of which some half a million suns reside. M 3 was discovered by the great visual observer, Charles Messier, who first observed this globular cluster on the faithful evening of May 3, 1764.
Every increase in telescope aperture provides an improvement to the view. Seen through my 12-inch F/5 Dob at powers of 250x or above, it is a truly mesmerizing sight!
Object 2: Messier 37
Though the large and imposing constellation of Auriga is now past its best for northern viewers, it is still very well placed fairly high in the western sky immediately after sunset. Binoculars capable of delivering an 8-degree field of view can just frame the three Messier open clusters( M36, M37 and M38) running through the belly of the constellation in more or less a straight line. Messier 37 is both the grandest and eastern-most of this trio of galactic clusters, and is easily tracked down in the finder of a small, backyard telescope.
At 26x (Celestron 25mm X-Cel LX) in the 130mm reflector, the cluster presents rather like a loosely packed globular cluster about the half the size of the full Moon, in a rich stellar hinterland of the Milky Way. But as one begins to increase the magnification beyond 60x or so, the true nature of this object manifests to the eye. The impressive light gathering power and resolution of the 130mm presents a gorgeous field of faint stardust comprising some 150 members. This cluster takes magnification quite well and is very much worth a closer look with a higher power ocular. At 118x (Meade Series 5000 5.5mm UWA), M 37 is an awe-inspiring sight, with stars of mostly equal glory filling the field of view. I feel it is the near uniformity of the brightness of the stars in this cluster that renders it so visually engaging, with a distinctly orange-tinted sun at the centre of the cluster; and you’ll definitely see that distinctive hue a little better in a larger aperture ‘scope. M 37 lies about 4,500 light years away from the solar system.
Object 3: Messier 44
The constellation of Cancer is distinguished from many others in that its brightest stellar luminaries(including Epsilon Cancri at magnitude + 6.3) are actually fainter than the most celebrated Messier object within its borders. I speak of course of the magnificent M 44, more commonly known as the Beehive Cluster, which is easily tracked down with the naked eye on a dark, moonless night as a large, roughly circular third magnitude glow, approaching the meridian about 10pm local time at the beginning of April. A wonderful object for large binoculars, which pull in about 60 stars, a medium aperture telescope greatly increases the tally of stellar members that can be seen, increasing the number to well over 100. Using my 25mm Celestron X-Cel LX eyepiece delivering a true field of 2.3 angular degrees at 26x in the 130mm f/5 Newtonian, the ~ 1.5 degree wide Beehive is very well framed for study. The field explodes with the light of mostly white stars, many of which(perhaps 20 per cent?) appear to be double or multiple in nature. Higher powers will, of course, pull in still fainter members down to magnitude +12 or so, but its glory is somewhat diminished owing to the inability of the same eyepiece to capture the entire cluster within its narrower field. This rather loosely arranged galactic cluster provides clues to its more advanced age, which is estimated to be about 800 million years. M44 is located at a distance of just under 600 light years from the solar system.
Object 4: Epsilon Bootis
Contrary to received wisdom(read parroted, armchair ignorance), Newtonian reflectors make very neat double star telescopes. I have personally been astonished how well they operate on these targets, having examined a great many systems with a variety of Newtonians over the last several years. Indeed, the 130mm f/5 has rapidly become one of my favourite instruments to divine double and multiple stars, where it has resolved pairs as tight as 0.9″ under ideal conditions. What is more, it is a decidedly better instrument than the finest 4-inch refractor money can buy, its extra light gathering power and resolution coming into its own particulalrly on fainter pairs. Our next target is not especially difficult to resolve but it does present as one of the spring sky’s most beautiful binary star systems. Also known by its more common name of Izar, it is easily located with the naked eye late on spring evenings, where it can easily be made out as a magnitude +2.5 field star off to the northeast of Arcturus. Through the 130mm reflector, Izar presents as a beautiful colour-contrast double with a bright orange primary(magnitude +2.8) and fainter, magnitude + 4.8 secondary with a soft bluish hue, giving rise to its latinised nickname, Pulcherrima (the most beautiful!). Intriguingly, the secondary is actually a sun-like star in its stage of evolution, yet the eye sees it as something altogether different! I love to observe Izar regularly throughout the spring and summer months with the 130mm, usually charging it with a power of 260x (Parks Gold 7.5mm coupled to a 3x Meade Barlow lens). On the steadiest evenings the Newtonian presents the stars as lovely round Airy disks, surrounding by a faint first diffraction ring. Separated by about 3.0″, it is best seen when the system rises to a decent altitude above the eastern horizon, which in early April, is not attained until around midnight or later. If at first you don’t succeed with this system, try again on a calmer night when it’s higher in the sky.
Object 5: Messier 81 & 82
On April evenings, Ursa Major lies very high in the sky and is ideal for observing objects within its borders. Our next target is a pair of bright Messier galaxies easily tracked down by following an imaginary line from Phecda (Gamma Ursae Majoris) through Dubhe(Alpha Ursae Majoris) and extending this line about the same distance again. Use your finder to look for a 7th magnitude smudge. If you find it hard to track down with your finder, try using a 10 x 50 binocular. The 5.1″ Newtonian charged with a power of 26x frames both galaxies very well within the same field, where I can easily make out a round, softly glowing smudge with a noticeably brighter centre. This is the celebrated spiral galaxy M81. Just half an angular degree to the north you’ll see a cigar shaped smudge about twice as long as it is broad and about a magnitude fainter; the irregular galaxy M82. For a better view, I like to crank up the power to 59x using an Explore Scientific 11mm (82 degree AFOV), which considerably darkens the sky allowing me to study both galaxies better in the spacious 1.35 degree true field. With averted vision, I can just trace out the faint spiral arms of M81, but in many ways I think M82 looks more interesting, as its smaller size makes its surface brightness that little bit higher than M81. M 82 appears distinctly mottled to my eye owing to prominent dust lanes coursing through its mid-section. It is also actively birthing stars. Both galaxies lie about 12 million light years away.
Object 6: Messier 51 & NGC 5195
Our next port of call doesn’t lie too far away from M81 & M82. Easily spotted in 10 x 50 binoculars as a 8th magnitude glow, Messier 51( the Whirlpool Galaxy) is easily tracked down about 3.5 degrees to the southwest of Eta Ursae Majoris, the end star of the Plough handle, and just across the border in Canes Venatici. Easily discernible as distinctly non-stellar at 26x in my 5.1″ f/5 Newtonian two distinct glows can be seen at a glance in the low power field. To get a better view though, crank the power up to beyond a 100x or so to increase the image scale and darken the background sky. At 118x in my 5.5mm Meade Ultrawide angle eyepiece, the view is quite compelling. Hints of the spiral nature of M51 can just be made out in this small telescope as can its smaller companion galaxy, NGC 5195. With good dark adaptation and averted vision, you may just be able to make out the famous luminous bridge ‘connecting’ the two. I find that the sky needs to be very transparent and still to glimpse this structure. It also helps being so high in the sky at this time of year where the effects of the atmopshere are less severe. Failing that, if you place M51 just outside the field of the view, examining NGC 5195 for signs of a slight increase in brightness in the space separating the two galaxies. Of course, M51 and NGC 5195 are much better seen in larger instruments such as my 12″ telescope, but it’s always good to visit this historically significant face-on spiral, as it was first delineated using the great 72 inch Leviathan of Parsonstown back in 1845 by visual means. Astronomers reckon NGC 5195 brushed past M51 about 100 million years ago and is now ‘behind’ it. Both galaxies lie about 26 million light years away.
Object 7: Messier 67
Our next object, the rich open cluster, M67, is often overlooked on account of the greater splendour of Cancer’s most illustrious object, M44. To find it, move your telescope a little under two angular degrees west of Alpha Cancri(Acubens). Easily visible in binoculars as a rougly elliptically shaped misty patch about the size of the full Moon, my 130mm Newtonian at 59x resolves this pretty cluster into a mound of several dozen faint stars quite similar to M37 at first glance, the brightest of which shine at the 10th magnitude of glory. Cranking up the magnification to 118x allows you to pick off many more members bringing the stellar tally upwards of 100. The faintest members of this 300+ strong cluster are not resolved in this small telescope but rather presents the illusion of nebulosity wreathing its way throughout its 25′-wide frame. To my eye, the stars are arranged in curious swirls with an overall shape quite reminscent of ‘incandescent seahorse’ set adrift in a vast ocean of space. The cluster is believed to be quite advanced in age; 3 to 5 billion years by most astronomers’ reckoning, and lies at a distance of about 2,600 light years from us.
To be continued…………
*** New testimonies recently added to the end of the article.
Mair inconvenient truths, ken.
For sheer brute force light gathering ability, Newtonian reflectors rate a best buy. No other type of telescope will give you as large an aperture for the money……For the sake of discussion, I have divided Newtonians into two groups based on focal ratio. Those with focal ratios less than f/6 have very deeply curved mirrors, and so are referred to here as ‘deep dish’ Newtonians. Reflectors with focal ratios of f/6 and greater will be called ‘shallow dish’ telescopes.
Pardon my bias, but shallow dish reflectors are my favorite type of telescope. They are capable of delivering clear views of the Moon, the Sun and the other members of the solar system, as well as thousands of deep sky objects. Shallow dish reflectors with apertures between 3 inches(80mm) and 8 inches(203mm) are usually small enough to be moved from home to observing site and quickly set up with little trouble………..Most experienced amateurs agree that shallow dish reflectors are tough to beat. In fact, an optimised Newtonian reflector can deliver views of the Moon and the planets that eclipse those through a catadioptric telescope and compare favorably with a refractor of similar size, but at a fraction of the refractor’s cost. Although the commercial telescope market now offers a wide variety of superb refractors, it has yet to embrace the long focus reflector fully.
From Star Ware, 4th Edition ( 2007), by Philip S. Harrington pp 32−33.
To savor stargazing we need to strike a balance between the time, energy, and expense devoted to this activity and what we channel into other necessary human tasks. A contented evening of stargazing comes with this balance. ‘In medio stat virtus’, or, as this Latin rendition of Aristotle’s maxim has been translated into English, “All things in moderation.’
Otto Rushe Piechowski
Sky & Telescope February 1993, pp 5
The trend towards larger and larger reflectors is indeed exciting, and I can understand the need to keep them short focus( typically f/4 to f/5). But why are so many small ones made with these focal ratios? Such telescopes bring out the worst in the Newtonian design. The 6 inch f/8s and 8 inch f/7s common many years ago, were much better and more versatile reflectors than many commercially available today.
Sky & Telescope, November 1993 pp 4.
Newtonian reflecting telescopes are great telescopes for observing Jupiter.
John W. McAnally, from Jupiter and How to Observe It, pp 152.
Indeed a high quality Newtonian reflector is a very powerful instrument, fully capable of superb performance in viewing the planets when the optics are kept clean and properly aligned. They have been amng the favorite instruments of serious planetary observers for many decades.
Julius L. Benton, Jr. from Saturn and How to Observe It, pp 57.
Newtonian reflector telescopes, apart from their complete freedom from chromatic aberration, can be made with much shorter focal ratios than refractors, usually between f/6 and f/8 so that even an 8 inch reflector is portable and easily affordable by most amateurs. An 8 inch refractor would be financially out of the question for the vast majority of amateurs and would need permanent housing in a large observatory. As a choice for planetary observation, then, there is a lot to be said for the Newtonian reflector in the 6 to 10 inch aperture range.
Fred W. Price, from The Planet Observer’s Handbook 2nd Edition, pp 41.
It is true that such reflectors are considerably less expensive than are refractors of the same size. This does not mean that they are not as good; in fact, Newtonian reflectors are more widely used by more experienced observers than any other type.
David H. Levy, from Guide to the Night Sky, pp 61
The simplest, cheapest and overall the most efficient design you could choose to use as a richfield telescope is the Newtonian reflector. As ever, an aperture of 100 to 200mm and a focal ratio of f/4 to f/6 is most appropriate.
Nick James & Gerald North, from Observing Comets, pp 57.
It is not proposed to enter upon the controversial topic of reflectors versus refractors. If does not grudge the extra attention to keep a reflector in perfect adjustment, its performance in revealing planetary detail will equal that of a refractor of the same aperture, particularly if it is mounted with an open, lattice work tube, when a further improvement may be derived from the employment of an electric fan to keep the column of air above the mirror well mixed.Moreover it has practically negligible chromatic aberration, whereas colour estimates made with a refractor are exceedingly unreliable.
Bertrand Peek, from The Planet Jupiter;The Observers Handbook, pp 37.
What is “over-expensive”? It depends on your point of view. A 106mm Takahashi flat field quadruplet refractor can be had, without mount, for only a little more than I paid for a high-end 12.5″ dobsonian Newtonian with state-of-the-art optics. If astro-imaging is your forte, the Tak will be the better choice. Don’t forget a high-end mount to go with it. For visual, though? Get real. The Tak will be severely limited–a well-machined, and beautifully-performing SMALL scope that can’t see much. If you buy your scopes for visual use, the Tak isn’t just over-expensive, it’s ridiculous. If you buy your scopes for photography, though, that Tak is an incredible choice.
Don Pensack from post no. 235 in an online a discussion on Why is Takahashi Overly Expensive?
Apochomats are expensive, particularly in the larger (repeated word ‘Larger’ omitted) apertures. Object the commonly available designs, reflectors are free of chromatic aberration since mirrors reflect all the colors identically. This means that a good quality reflector with a large aperture can be free of false color and yet provide the resolution and fine scale contrast while still being affordable. These Scopes have issues of their own..
Jon Isaac, from post no. 14 in an online discussion entitled, Can An Apochromatic Refractor Use More Powerful Eyepieces than an Achromatic Refractor Of The Same Size?
So What telescope Should I Spend with My Money On?
All in all, if you can afford it, and if you have the room to house it permanently in some sort of observatory (perhaps a run off shed), I would say go for a Newtonian reflector of 10 to 14 inches (254 to 356mm) aperture and as large a focal ratio as you can reasonably accommodate……..If you can’t afford a 10 inch then go for a smaller Newtonian reflector. Remember this type of telescope is the cheapest of any but please do not compromise on quality for the sake of size. My second choice for an instrument intended for visual observation of the Moon would be a refractor of at least 5 inches (127mm) aperture…
Gerald North, from Observing the Moon; the Modern Observer’s Guide (2007), pp 52
A first-rate 130-mm Newtonian is roughly equivalent to a first-rate 102-mm refractor for planetary observing, but superior to the refractor for all other purposes.
Tony Flanders, former Associate Editor, Sky & Telescope, in an online discussion ( post no. 1837) of the Astronomers Without Borders One Sky Newtonian.
The Newtonian reflector is a popular choice. Money wise, they are cost effective, and most importantly, you can obtain a large aperture telescope for a reasonable sum of money…..It is true the Newtonians can come with long tubes if a longer focal length and high focal ratio is required…..Although you will hear it said high focal lengths and ratios( example f/7 etc) are desirable for planetary work, telescopes with a focal ratio of f/5 can be very satisfactory.
Paul Abel, BBC Sky at Night Presenter, from his book, Visual Lunar and Planetary Astronomy (2013), pp 14/5.
The best view of Jupiter I ever had was at Peach State with a 12.5″ Portaball on an equatorial platform at 567x (10/10/2010). There was so much detail I tried to find a larger scope in use (no luck, alas). We could see albedo features on Ganymede and Callisto. Amazing what you can see on a night of exceptional seeing. Even when the seeing is not at its best, I find there are often times on any night when a larger scope has an advantage.
Alan French, from an online discussion (post no.14) entitled Large Telescopes and Jupiter.
Guan Sheng Optical (GSO) uses high-volume, state-of-the-art, high quality manufacturing and test lines. GSO guarantees diffraction limited performance, but their mirrors typically have a mirror surface quality of 1/16 wave RMS at least, and often better. This very smooth mirror surface results in excellent optical performance with practically no light scatter, while Antares Optics secondary mirrors are 1/15 P-V or better and come Zygo tested;
Rob Teeter, founder of Teeter’stelescopes.com
Amateur astronomers and telescope makers have debated from time immemorial the advantages and disadvantages of different telescope designs. In particular, mountains of hard copy and electronic articles are available on the merits of refracting and reflecting telescopes, more recently, apochromatic refractors vs. Newtonian reflectors. This debate has become rather rancorous (Newtonian telescopes as APO “killers” comes to mind.) and unscientific, to say the least. And when all is said and done, in a discourse without loaded words and acrimony, a discussion devolves to one concerning perfect optics. And isn’t this what we all want or wish we had?
From Ed Turco’s online article: The Definitive Newtonian Reflector.
Many people shy away from Newtonians because they have exposed optics that get damp and deteriorate. In this respect a good closed tube Newtonian wins hands down over an open tube one, as the tube keeps dew at bay. For the best planetary resolution, a telescope must, must, must must be precisely collimated!!! Also, the optics should be able to cool down quickly by fan cooling. Mirrors thicker than 40mm have serious cooldown problems unless fan cooling is employed. My 254mm f/6.3 Orion Optics Newtonian (plus mirror fan)is the best planetary telescope I have ever used. Some planetary observers line their tubes with cork too, to reduce currents. Many good planetary telescopes are comprehensively ruined by being in a huge unventillated dome with a narrow slit, a concrete floor and a metal dome.
Martin Mobberley, Author, from his webpage: Telescopes.
See also his review of the same instrument here.
Much has been written on the subject of the central obstruction and its impact on fine planetary detail. It remains a hot-button topic in on-line forums, and yet, despite the intensity of the debate, obstruction effects are well understood and fairly simple to quantify. The issue was most elegantly summarized by William Zmek in the July 1993 issue of Sky & Telescope magazine. Zmek’s rule of thumb states that if you subtract the diameter of the obstruction from the objective, you have the equivalent unobstructed instrument when it comes to contrast resolution. In other words, an 8-inch reflector with a 1.5-inch obstruction has the potential to resolve the same low-contrast planetary detail as an unobstructed 6.5-inch scope.
Gary Seronik, former Sky & Telescope Contributing Editor and Author, from his personal website.
I have the 12″ Orion as well (Truss, but the same thing otherwise). I have seen two other instances where optical quality on this model was excellent, and my own has perhaps the best mirror I have seen in a mass market dob.Star test with 3% obstruction shows an identical secondary shadow breakout, and the mirror had no zones or turned edge, and the smoothness was quite good. In other words, by anyone’s measure, the mirror in my own sample is a really fine mirror. If yours is in the same category for quality, be prepared for some awesome planetary views. The 12″ easily put up better planetary views than my 6″ Astro-Physics Apo and my C14. Views with 31mm Nagler and MPCC Coma Corrector are wonderful (I use the MPCC because it is 1x and while maybe not quite as sharp as the Paracorr, that 1x is important when trying to get the largest field possible out of today’s very expensive wide field eyepieces. I had fantastic views with my 12″ and it is my favorite larger aperture telescope ever. It does everything with excellence.
Eddgie, from an online thread entitled, First Light with my XT12G.
I tested the scope over a four week period, and found the optics to be very good, to excellent. I star tested the scope extensively, and found the mirror to be extremely smooth, with the slightest under correction.. I couldn’t put a figure on it, GS advertise 1/12 wave. Planetary images were rock hard. I tested the scope against my friend’s 12.5 Inch premium Dobsonian, which sports a “Swayze” mirror, and we couldn’t split the images over four different nights. On one particular night of excellent seeing, I had the magnification up to 500x, without any image breakdown.Our local club Telescope guy ran a series of tests on the optics, the main one being a Double pass Ronchi test, against a certified optical flat. He informed me the mirror was very well corrected, and very smooth. He didn’t believe the price I paid for the entire scope.
In summary, this scope has been a huge surprise. My experiences with “light Buckets” previously were not great. My intention was to use this scope for deep sky observation only, as I already have a Zambuto equipped premium scope for Planetary work, but it’s a lot more than that. Since purchasing my scope, I have looked through fourteen of these instruments at our club nights, and the images in all of them are almost identical. Guan Sheng seem to be producing a great mass-produced scope.
Astronomical Society of Victoria Inc
From a review of the Guan Sheng 12″ f/5 Dob (essentially identical to the author’s instrument pictured above). Source here.
I purchased a 15” Obsession from owner David Kriege on January 12, 2007 and took delivery in the first week of March of the same year. Since that time it has been my principle telescope for visual use. For comparison, I have owned two Takahashis (FS-102 and TOA 130), three Televues (TV85; NP127; TV85 again), a WO 10th anniversary 80mm, an 8” Celestron SC with Starbright coatings and a 6” Orion dobsonian.Despite the demonstrated affinity I have for apochromatic refractors, I had been to enough star parties to learn that aperture ultimately wins…………Those interested in purchasing a larger dobsonian may wonder what you see in a 15” scope. Having compared views with everything from 60mm refractors to a 30” dobsonian, I can honestly say “more than enough to keep you busy for a long, long time”. Globular clusters really seem to take life at about 12” and galaxies are already more than nondescript smudges by 15”. Of course local conditions make a huge difference. I have had nights with a 5” refractor that gave the 15” a run for its money. I have been at star parties looking at a galaxy in the 15”, then wandered next door to a 24” expecting to be utterly blown away by the difference and then been surprised by how little there was. That said, on any given night, the 15” tends to beat the socks off my small refractor nearly every night across the board, from planets to wisps.
From a review of the 15″ Obsession Dobsonian by Rene Gauge. See here for more details.
The Oldham optics on this Dobsonian are superb. A number of tests were carried out, the results of which are outlined below. The round airy discs of bright stars appear perfect. Faint stars are fine razor sharp points of light. On nights of good seeing I have been able to see faint diffraction rings around stars. Images snap into focus even at high power.
After extensive star testing, I could detect no major defects. There was no sign of any astigmatism, even close to focus. The test revealed near perfect correction and very smooth & high contrast optics. Given that the primary mirror is large and fast, and the star test is particularly sensitive, I consider these results to be very good. A particularly impressive aspect is the ability of the optics to handle very high powers. The results of the magnification roll-off test were excellent. First light revealed that the mirror could easily handle forty times per inch of aperture on planets. In good seeing conditions Saturn would reveal a high level of detail and remain sharp at magnifications in excess of 600X, and Jupiter showed no sign of image breakdown at 507X. Under no circumstances have I ever seen Jupiter soften at powers less than 450X. I have even enjoyed good views of the moon at 888X. I have also shared my experiences with a number of experts around the world who believe as I do that the optics are performing to a high specification.
Nick Koiza, from his review of a David Lukehurst 16″ f/4.4 Dobsonian detailed here.
Here’s what everyone wants to know. The primary mirror, as with all Zambuto-equipped Starmasters I’ve seen, is a jaw-dropper. Since quoting data on the mirror is often misleading and can cause flame wars, I’ve chosen to leave these out of this review. What I will say is that the Zambuto mirrors have an extremely smooth optical surface, with a near-perfect star test. Running through focus, the Fresnel rings are identical on both sides of focus and evenly illuminated. I can find no zones, no turned edge, and no astigmatism. There is perhaps a “slight” under-correction, however it’s often not even noticeable to me, which could indicate that I might have tested while the mirror was still slightly out of thermal equilibrium. If it is there, it’s very, very slight & I couldn’t begin to guess by what fraction of a wave.
However, that smooth surface correlates to what I believe to be the most important aspect of visual observing, and that is contrast. In a word – exceptional. The scope shows even the most subtle differences in illumination. There is definitely an emotional response with Carl’s mirrors, an underlying feeling that’s hard to describe, except to say sitting at the eyepiece is more like observing from space rather than the ground. The extremely fine details seen are amazing, and sometimes I seem to subconsciously pick up things that I don’t notice when looking through other instruments, only to go back to my scope & find that I wasn’t dreaming!
Jupiter usually shows 10 bands and massive amounts of detail within the belts & GRS, as well as the festoons & barges. And being able to see this kind of detail routinely at 400x, and many nights up to 600x is definitely like looking at a photograph. Polar regions & surface detail are visible on Io. Saturn shows the Crepe ring every night, as well as the Encke minima without fail.. Despite the short focal length it is a killer planetary scope. When Mars was last at opposition before the dust storms, picking out surface details was as easy as looking at our moon. In addition both polar caps were easily seen. Phobos & Deimos were also seen. On the planets I rarely use filters, so most of the views described above were natural.
No matter the conditions, the Trapezium easily breaks into 6 components, even at very low magnifications. The detail level seen in M42/43 is far better than any photo I’ve ever seen, from low-power views that show the entire nebula, to using a binoviewer at 500x on the Trapezium vicinity that reveals details in the nebula, which are reminiscent of the structure seen in cumulo-nimbus clouds.
With globular clusters, “resolved” takes on a new meaning & the scope provides “in your face” visual observing! Obviously M13 & Omega are completely resolved. One of my favorite globulars is M92 because of the super-dense core that seems to go on forever. One night I decided to push the scope to what our group likes to call “silly power” & view M92 at 700x. WOW – the core showed a tremendous amount of resolution, but again it’s so dense I couldn’t quite get it to go all the way. M13 at this power was like looking right through it to the other side. And I can’t forget the extra-galactic clusters, G1 & G2 in M31. G1 actually started show resolution at about 500x. Another extra-galactic object is NGC 604, the giant HII region in M33, about 2.5 MLY away. At 700x I can see much structure & filaments within the nebula. Seeing that in real time is spectacular.
Most galaxies within the local group show quite a bit of structure, knotting, & dust lanes. Those more distant objects do reveal detail well above being mere smudges. Many Virgo galaxies show spiraling. Every component of Stephan’s Quintet is always visible, and much easier to see than in many other scopes of similar aperture I’ve used. NGC 7331 is stunning. Closer neighbors like M51, M31, M33, M81/82, M104, NGC 4565 & NGC 891 take on photographic qualities in the eyepiece. I’ve been able to determine the rotational direction of a galaxy that NSOG stated was over 500 MLY distant. The scope is also quite capable of hunting the faint Abell planetary nebulae & galaxy clusters, and with an H-Beta filter, the Horsehead is a snap with direct vision. These are just a few of my experiences at the eyepiece. In short, once the mirror has reached thermal equilibrium, it’s like having a 14.5″ f/4.3 APO. Tight, pinpoint stars sharp across the FOV, and a nice “snap” to focus – there’s no mistaking it. The low f/ratio provides a nice wide field, at least for a scope of this size. I can get 1.4* with the 31 Nagler & using the Paracorr which boosts the focal length from 1584mm to 1822mm. (1.6* without it) Not a bad FOV for a 14.5″ mirror.
From a very happy and experienced owner of a 14.5″f/4.3 Starmaster Dobsonian. Details here.
Like every Sky-Watcher scope I’ve tested, this one arrived perfectly collimated out-of-the-box, and has held its collimation over the period I’ve been testing it. This speaks highly of the mechanical integrity of the scope, and alleviates the beginner’s greatest anxiety about Newtonians. No doubt the scope will require collimation at some point, but if it can make it to Canada to from China without losing collimation, it should be pretty stable.
I tested the telescope under the stars on four different nights, exploring a wide range of objects. Well, actually, one night and three mornings, as I was unable to resist the lure of using this scope on my old favourites, Jupiter and Saturn, currently in the predawn sky. I also spent time looking at the Moon, Mars, and Venus, favourite double stars like Epsilon Lyrae (split easily at 120x) and Rigel, and deep sky showpieces like the Ring Nebula and the Orion Nebula. All were well shown, as one would expect in a good quality 150mm scope. The supplied eyepieces, 25mm and 10mm “Super” modified achromats with 50° fields, performed quite well, yielding magnifications of 48x and 120x. This scope showed that it can handle much higher powers easily; I found myself using a 6mm eyepiece (200x) on the Moon and planets most of the time. Fans of deep sky objects will probably want to add a 2″ eyepiece to take in the wide field of view this scope is capable of.
As Terry Dickinson says in NightWatch, “There may not be a perfect telescope for the beginner, but the closest thing to it is the 6-inch Dobsonian-mounted Newtonian reflector.” The Sky-Watcher 150mm is an excellent example of this breed, at a very attractive price. My wife and I usually donate a telescope to our favourite charity to auction off each year, and this year this scope is our choice. Highly recommended!
I put together one of his 6″ f8 telescope kits with the help of my kids. It’s still one of my favorite scopes. These days, I lend it to people who have shown an interest in astronomy, but can’t afford a telescope.
Changing technologies have meant that amateur telescope making has largely been replaced by the purchase of accessible high quality commercially produced instruments, but the Western world’s passion for the night sky is as strong as ever, and long may it continue.
Dr. Allan Chapman, from an essay entitled: The First Astronomical Societies, Astronomy Now, January 2018, pp 49.
Optical quality matters, but these days it’s usually not the main problem. Most of the commercial mirrors I’ve evaluated in the past 10 years have been pretty good — a few have even been excellent. That’s not to say there aren’t duds out there, but if your telescope isn’t performing, the items that top this list are more likely to be the reason.
Gary Seronik, from an online article entitled: Five Reflector Performance Killers.
In this department of astronomy, the names of Herschel, South, Struve, Dawes, Dembowski, Burnham, and others are honourably associated and it is notable that refracting-telescopes have accomplished nearly the whole of the work. But reflectors are little less capable, though their powers seem to have been rarely employed in this field. Mr. Tarrant has lately secured a large number of accurate measures with a 10-inch reflector by Calver, and if care is taken to secure correct adjustment of the mirrors, there is no reason why this form of instrument should not be nearly as effective as its rival.
W. F. Denning, from Telescopic Work for Starlight Evenings (1891), pp 290-291.
Since about a month this telescope is parked in my garage.
It is a Newtonian of 158mm aperture and a focus of 1240mm.The primary and secondary mirrors were made by David Hinds of UK.The telescope was home-made by my friend Tavi aka Erwin.Because he have other commitments, I was offered to give it a ride. I used the oculars seen in the second picture, from left to right: HM 6mm, Galilei – 50 mm, Galilei – 9mm , Baader Classic 6mm Ortho. This are the double.multiple stars observed on 23rd of December. All stars were split except 52 Ori where I believe to see a black space between main star and companion but not 100% sure.I was very pleased to see very well E and F stars in Trapezium.Good telescope, excellent optics, reliable mount……..I continued the testing on 26 of December when I made observations of 36 And, Delta Gem , Theta Aur and Eta Ori. All eas(i)ly split ,beautiful views……………..On 14 of January I targeted 7 Tauri double star. Unfortunately on the rare occasions when the stars were visible, the sky was hazy but still seeing was not better than 5 to 6 Pickering. Like with 52 Ori ,also at 7 Tau double star the Hind telescope showed at 248 x the two touching Airy discs but no black space bewteen them. I have high hopes in good seeing this telescope will split 0.7” double stars.
Visual report on the 12.5” f/6.5 Teeter Dob with Mike Lockwood mirror.
My eyepiece ‘fleet’ with the 12.5″:
31mm Nagler 67x
24 mm Explore Sci 86x
17.3mm Delos 119x
12mm Delos 172x
8mm Delos 258x
5mm Nagler 413x
6-3mm Nagler Zoom 344x to 688x
The first two nights (Tuesday and Wednesday) of observation were very foggy and absolutely dew-drenched – the most dew I have ever seen. Both nights the main mirror dewed up just after midnight – the joys of a thin 1.1” mirror which tracks ambient temperature very well, I suppose….
Along with the dew was some of the best atmospheric steadiness I have ever experienced. I would place the seeing at 9 to 9.5 (pickering) out of 10. With a 3mm eyepiece (688x) on a 4th mag star near the zenith, the full diffraction pattern was stable and almost unmoving. Unfortunately the transparency was mediocre and, towards midnight, increasingly poor….
The third night (Thursday) was very transparent and drier, with much more manageable dew but the seeing was extremely poor. The close pairs of Epsilon Lyrae were two touching fuzzballs (the night before you could have driven a HumVee through the blackness between…)
I looked at a bunch of double stars the first night… I used my Nagler 6mm – 3mm zoom which gives magnifications from 344x to 688x. Close pairs seen were:
STF 186: sep. 0.8”, mags 6.79/6.84
wide, dark sky split. The dark space was equal in width to the central discs of both components. very delicate first rings were present at all times…
A 1504: sep. 0.6”, mags 8.84/8.92
darkline split. Central discs ‘kissing’… first rings were pretty much too faint to see…
BU 525: sep. 0.5”, mags 7.45/7.47
very deep notch. a black or grey line seemed visible at times..
STF 346 AB sep.0.5” mags 6.19/6.21 This is triple star 52 Arietis. The ABxC pair is at 5” separation… Very nice to see three stars here. The AB pair was a deep notch, again with fleeting glimpses of a line between…
Dave Cotterell, Madoc, Ontario, from an online thread entitled: 12.5″ f/6.5 Teeter Dob with Lockwood Glass.
This report details my visual and photographic observations of some sub-arcsecond double stars that have been the subject of a few CN threads the past few months. This document is necessarily heavy on technical details to support those who may wish to independently evaluate the results.
Visual observations were made with a 15-inch f/4.5 Dobsonian reflector setting atop an equatorial platform. All observations were made between September 26th and October 26th of this year with a Paracorr Type I lens (setting no. 1) in the optical train. In all cases, Pentax lenses were used to achieve the following magnifications: ‘low’ (5XW; 398x), ‘moderate’ (3.5XW; 569x), and ‘high’ (2.5XO; 798x).
Imaging was accomplished using an ASI 178MC cooled camera [AVI files; mono mode] in an optical train consisting of a Paracorr Type I lens (setting no. 5) and a 5x Powermate. The plate scale for imaging was previously determined to be 0.0553 +/- 0.001 “/pixel using calibration stars (n = 10) and 0.0553 +/- 0.002 “/pixel using a diffraction grating with monochromatic red light (n = 8). Sharpcap 2.8 was used as the image capture software. Fine focus was achieved using a Bhatinov mask [All-Pro, Spike-a brand] modified to fit over the Obsession UTA. Separation values were determined using REDUC. Images were stacked and processed using Registax with final presentation formatting in Gimp.
Bu 720, 72 Pegasi
magnitudes: 5.7, 6.1
position angle: 105 degrees
separation: 0.575” (orbital elements estimate); 0.505” (last precise measure; 2015)
The separation data are not in good agreement for this object. This is, therefore, a good candidate for quantitative scrutiny.
At 398x the object vacillated on the border between elongated and just resolved to two golden-orange disks of similar magnitude in the correct position angle; 569x proved sufficient to show the stars as different magnitude and clearly resolved (but not yet split); a final increase in magnitude to 798x showed the pair as split, again with a golden-orange color and a small difference in magnitude. The ease of resolution at modest magnification led me to think the larger separation value [0.575”] was more accurate for Bu 720.
Bu 720 was easily imaged using an exposure of 10 ms [gain = 320]. Four movies were made and separation was measured by three methods using REDUC: cross correlation of the top 5% of frames using S4 filter; simple measure of a Registax composite; and simple measure of a composite generated in REDUC. There was good agreement across these methods, giving a measured separation of 0.61”.
STT 20AB, 66 Piscium
magnitudes: 6.1, 7.2
position angle: 176 degrees
separation: 0.598” (orbital elements estimate); 0.59” (last precise measure; 2015)
Good agreement between WDS listed separation values. Should be able to split at moderate magnification.
Low magnification (398x) shows two white stars that are clearly resolved and are oriented in the position angle as stated in the WDS. Moderate magnification (569x) shows that the components possess dissimilar magnitudes; the pair was barely split about 20% of the time at this power.
STT 20AB was imaged using an exposure of 12 ms [gain = 400]. Four movies were made and separation was measured by two methods using REDUC: simple measure of a Registax composite; and simple measure of a composite generated in REDUC. There was good agreement across these methods, giving a measured separation of 0.59”. REDUC Correlation methods were not useful with this target for producing separation values because of the faintness of the secondary.
16 Vulpeculae, STT 395
magnitudes: 5.8, 6.2
position angle: 127 degrees
separation: 0.849” (orbital elements estimate); 0.81” (last precise measure; 2015)
This target possesses a wide discrepancy between WDS values and was discussed at some length in a prior CN thread.
This object was observed as split using an 8-inch reflector at 340x (3.5XW lens).
16 VUL was imaged using an exposure of 14.5 ms [gain = 450]. Four movies were made and separation was measured by three methods using REDUC: auto correlation of the top 5% of frames using S4 filter; stacked REDUC reductions; and simple measure of a composite generated in REDUC. There was good agreement across these methods, giving a measured separation of 0.771 +/- 0.006”. Previous REDUC autocorrelation measurements of this system using a 2x Powermate [plate scale = 0.143 “/pixel] gave a measure of 0.78 +/- 0.02”.
Mark McPhee, Austin, Texas, from an online thread entitled: Examination of Some Sub-Arcsecond Doubles: Bu 720, STT 495, Bu172AB, STT 20AB, and 16 VUL
yea sometimes (like this evening) I ask myself too: “why you silly id… buy all this expensive apo stuff???”
Cloudy for the whole day – this evening reported to be one of the most interesting of the year – Io & Europa before Jupiter – together with their shadows and crowned by the GRS. Before 1,5h I saw a break in the clouds and to be fast I just grabed my 8″ GSO Dob and took it out. After 30min cooling another break off – I could see so much detail in the bands, GRS shining in a bright red, both shadows, Europa just beginning to leave the planets disc and – man – I could swear to see a round structure in the band that could have been Io… – best experience for a looong time!
So go get a 8″ f6 Dob – Houston out
Donadani, Germany, from an online thread entitled; How much increase in aperture to see a difference?
Hello Peter [Natscher],
Hope you are well.
An 8 inch Portaball with a Zambuto mirror on a tracking platform is going to show you much more than a 130mm telescope, even a Starfire 130EDF. Both of these will be sit down and observe telescopes. If you were not going to get a tracking platform, I would go the refractor route. You will want tracking for dedicated planetary or lunar observing. Shoot, you could roll the dice and get a Sky-Watcher 8″ f/6 collapsible Go-To dobsonian. I have the non motorized version and it has a great mirror, however, your mileage may vary on the chinese mirrors.
Tony M, from an online thread entitled: 5″ Refractor or 8″ Newtonian for Lunar/Planetary Observing.
I would take a high-quality 8″ f/6 on a GEM over a 5″ refractor. The GEM will negate all the disadvantages of the Dob. My old Meade 826 easily gives me a sharp, detailed Mars at 400x (conditions willing). I wouldn’t trade it for any 5″ scope ever made.
Rick Woods, from an online thread entitled; 5″ Refractor or 8″ Newtonian for Lunar/Planetary Observing.
I may be too late to add my .02, but it should be valuable.
I have owned a AP130EDF and the GT model. I now own an 8″ f/5.5 Portaball.
My conclusion: The Portaball rips the APs to shreds. A perfect 8″ mirror over a perfect 5″ lens…no comparison, obviously assuming collimation and thermal equilibrium. Especially since the Portaballs are constructed with fans and other ergonomics to help with the thermal adjustment. And I’m solely talking about visual planetary, since that is almost exclusively what I do.
Markab, Kansas City, from an online thread entitled: 5″ Refractor or 8″ Newtonian for Lunar/Planetary Observing.
One should never lean too heavily on sketchers. Although the vast majority are genuine, some go to an imaging website, study a particular image, and fake a sketch. In this way, they can make a 4 inch peashooter telescope look better than a Hubble image. I’d put more faith in the unlying eye of a CCD camera than any sketch, however elaborate.
A major reason refractors give images with higher overall contrast than reflectors is that objective lenses may scatter only approximately 2% of the light passing through them. This is why I believe that the high refelectivity coatings that are now applied to many astronomical mirror surfaces are so important. With 95% reflectivity, not only will they give somewhat brighter images but they will also greatly reduce the amount of scattered light, so improving the overall contrast. A high reflectivity coating is well worth having even at an additional cost; not only will the telescope perform better but a second advantage is that the mirror surface allows far less moisture to penentrate and is likely to last perhaps 25 years before it has to be recoated. I have a 10 year old Newtonian whose mirror was one of the first to be given a high refelctivity coating and it still looks like new………The overall design of the telescope will affect the overall contrast as well. It is impossible to beat a well designed refractor, but Newtonian telescopes, where one observes across the tube assembly to the far wall, are almost as good.
Ian Morison, from An Amateur’s Guide to Observing and Imaging the Heavens (2014) pp 10.
A Newtonian for All Round Use
A very good compromise in designing a 200mm Newtonian is to use a focal ratio of f/6, and many such telescopes are sold with this basic specification. The focal length will thus be 1200mm, and the field of view when a low power, wide field, 2 inch eyepiece is used will be approximately 2 degrees. The secondary mirror willprobably be approximately 50mm in diameter, and this would give a percentage of obstruction of 25% and provide full illumination over the central 25mm diameter region of up to 46mm diameter field of view. This is a good compromise, but some manufacturers, such as Orion Optics in the UK allow the purchaser to choose other secondary diameters should he or she wish to optimise the telescope towards planetary (approximately 36mm) or widefield imaging (approximately 60mm). One could even purchase two flats for use depending on the type of observations planned for a given night!
Ian Morison, from An Amateur’s Guide to Observing and Imaging the Heavens (2014) pp 64.
Yes, I have active cooling for my 10″ Dob. For that scope, a fan in a baffle below the primary works fine. I have an EdgeHD 8″, a SW120ED and a 10″ solid tube Dob, and I know how Jupiter looks in all three. No 7″ APO in the stable, but aperture does count for something. Some of my best views of Jupiter have been through the 10″ Dob during early morning. All of my best views of Jupiter have been through the 10″!
Sarkikos, from an online review of the Celestron EdgeHD 8 inch SCT.
Making a good 8 inch Newtonian by Toshimi Taki (Japan).
I think I can speak with at least a little credibility on this subject, having owned numerous large refractors:
One of only two Christen 6″ f/15 folded Triplets
8″ Alvan Clark
and having used several other premium 8″, 10″ and 12″ refractors.
As a recovering “refractor-holic” I still crave their look, fit and finish. And inch-for-inch they can’t be beat. But an 8″ or larger refractor w/mount is a true BEAST to own unless you can leave it permanently mounted. Topping it off there’s that little thing called “COST”!
Once we started having master mirror makers like Carl Zambuto et.al. turning out mirrors that were simply without compromise, optically – the paradigm shifted!
A premium 12.5″ reflector today will simply blow away that beautiful old 8″ Clark. My present 14.5″ Ed Stevens mirror produces planetary images that are superior to anything I ever saw in a 10″ Zeiss triplet and pretty darn close to the 12″! And don’t even get me started on comparisons with my 28″ Starstructure w/Steve Kennedy mirror! This scope is fully driven and features GOTO, yet I can set it up, take it down and transport it (easily) all by myself. Try to picture what a 20″ refractor would look like and cost…that’s about what it would take to begin to match the performance!
Would I love to have a giant TMB set up in a dome behind my house? Sure! But not for ‘performance’ reasons.
Mike Harvey (Florida), from an online thread entitled: Refractor Versus Reflectors.
My 6″ refractor [AP 155] will show the arms of M51 from a dark site, but fairly subtly. It’s far behind what my 10″ Dob can do in that area.The inability of the refractor to show much spiral detail in galaxies is probably its greatest drawback as a deep sky instrument.
Joe Bergeron, (Upstate New York, USA), from an online thread entitled: Refractor Versus Reflectors.
My advice to everyone wanting better planetary views is is to always spend money on a better instrument, or make their instrument better than it is. An 8″ f/6 reflector with a high quality mirror is one of the best planetary scopes money can buy. Period. Don’t be duped into thinking a 6″ MCT is going to be better. Physics simply do[es]n’t permit it.
Ed Moreno, from an online thread entitled:8 inch f/6 Dob versus 6 inch Orion Mak on the Moon and Planets.
I’ve tried a single curved spider in my 8 f7.6, but went back to the straight 4 vane after a year. Didn’t notice even a tiny hint of more fine detail on Jupiter with the curved vane.
Planet Earth, from an online thread entitled: Curved Spider Vanes?
The idea of curved-vane spiders isn’t new — the concept has been around for a long time and several designs were detailed in the May 1985 issue (page 458) of S&T. For telescopes up to 12-inch aperture, a curved spider can be a good alternative to traditional 3- or 4-vane spiders. With larger scopes, the diagonal mirror typically becomes big and heavy enough that the greater rigidity offered by conventional spiders or more robust curved ones may be required. I’ve successfully used the design described here in numerous telescopes, including my 12¾-inch. My single-curve spider has the added benefit of being simpler than the ones in the 1985 article, and therefore easier to build.
Gary Seronik, from his online article: How to Build a Curved Vane Seconday Mirror Holder.
This is essentially an aesthetic issue. If you don’t like spikes, then go ahead and get a curved vane spider. It does eliminate the spikes. You will see an even glow around bright objects like Jupiter or Venus, and nothing around everything else……..If the spikes don’t bother you, then stick with a straight vane.
Jarad, from an online thread entitled: Curved Spider Vanes?
I have put a 6″ APO up against a mass market 8″ f/6 reflector and I can tell you that the 6″ APO overall is a better performer. It is sharper everywhere in the field, had better planetary contrast, and came SURPRISINLY close in terms of deep sky (Globular and Galaxy) performance.
But this didn’t have much to do with the fact that it was a refractor vs a reflector, but rather more to do with the fact that is is a virtually PERFECT refractor up against a telescope with optics that were only “Fairly good” optically.
But.. IF you were to put a TOP QUALITY mirror in your scope, along with the highest quality diagonal you could find, you would find that on axis, it would indeed take refractor very close in size to yours to give a better visual image at the center of the field.
Ed Moreno, from an online thread entitled: Refractor Equivalent to a 8″ Reflector.
A good 7.1″ refractor is very close to a good 8″ reflector on M13. For planetary resolution most of the time the 7.1″ refractor beats the good 8″ reflector. But, they can be very close on a good night.
Rich N (San Francisco Bay Area), from an online thread entitled: Refractor Equivalent to a 8″ Reflector.
As I mentioned earlier in this thread my experience is that a 7.1″ refractor is very close to an 8″ Newt.
I’ve had my AP 180EDT f/9 APO side by side with a friend’s well made 8″ Newt a number of times. My refractor is more consistant in giving high contrast, high resolution images but on the right night that Newt can give some fine planetary images. For deep sky the views are very similar.
Rich N(San Francisco Bay Area), from an online thread entitled:Refractor Equivalent to a 8″ Reflector.
I’m not talking about local seeing from night to night. I’m suggesting that if you set up a high end APO and a high end Newt of roughly the same size (maybe a 180mm APO and 8″ Newt) side by side over several nights, the APO (refractor) will more often show better high res, high contrast, planetary detail.
Rich N(San Francisco Bay Area), from an online thread entitled:Refractor Equivalent to a 8″ Reflector.
No, a well crafted 8″ reflector with a Spooner f/7 mirror will totally outclass not only 5 or 6″ achros, but 5 or 6″ apos as well. And look at the original posters question again. He was wondering if an 80mm refractor would equal a 6″ reflector or a 100mm refractor would equal an 8″ reflector. No, and it’s not really close. And if you can tie your shoe you can collimate a reflector and clean the mirror once a year.
And my 6″ $250 Orion 6″ f/8 Dob has run totally neck and neck with my buddy’s Tak 102 on more than a few nights on the moon and planets. And it’s beaten the 4″ apo on some nights. Same result with a TV102 and a Vixen Fluorite 102. And it beats my TV85 and his Tak 78 100% of the time. Myths die hard.
I routinely compare 6″ APO to 7″ and 8″ Zambuto reflectors – see my sig for specifics. I am a dedicated planetary observer and really enjoy such comparisons.
Basically, I’ve found that the 8″ Z-mirror when cooled will be ever so slightly better then the 6″ APO. And the 6″ APO will edge out the 7″ reflector. The 6″ APO, an FS152, is a doublet and does not focus all colors to a common point as a matter of design. The blue is thrown way out of focus so the image has a slightly warmer look to it then that of the reflectors. I have often wondered if a triplet was compared to a the 8″ reflector how it would perform. Probably the same as the doublet as resolution is primarily a function of aperture.
The differences are quite minor in good seeing. But when the atmosphere is unsteady, I prefer the views in the FS152 over everything.
Peleuba(North of Baltimore, MD), from an online thread entitled: Refractor Equivalent to a 8″ Reflector.
I have a nice C6-R with a Chromacorr, and a nice 8″ f8 newt with a very fine Raycraft Primary, Protostar secondary, and flocked interior. I can’t recall offhand the size of the secondary, but it’s scaled for my 2″ EP’s, so it’e bigger than is optimal for planets.
Aestheticly, I find the refractor better, especially on evenings of dropping temps. I know the refractor has to cool too, but the views seem to be sharper sooner, and I never see tube currents.
The newt does reach deeper, though. But, I generally like to see sharper than deeper for the kinds of things I use the refractor for (planets and clusters). When depth is the concern, I opt for more aperture.
Under ideal conditions, I’m sure my 8″ newt will out-perform the refractor. But, conditions are rarely ideal, and so the edge goes to the refractor– tends towards better sharpness and better contrast due, I think, primarily to the lack of tube currents and cooling time.
Apples to Oranges, though.
Kerry R (Mid West Coast, Michigan), from an online thread entitled: Refractor Equivalent to an 8″ Reflector.
I will go toe to toe with any 7″ or 8″ APO with my 8″ F8 Newt and my Dan Joyce 8″ f/6.7 Newt. In the end I paid very litte for both Newts, and the 8″ APO owner has paid big time for the 8″ APO and it’s mount.
Had my share of 5″ to 7″ APO’s and they just dont cut it for such a high price. They do give that super fine snap to focus image, but my well built 8″ Newts can pretty much do the same thing and cost 50x less.
CHASLX200 (Tampa, Florida), from an online thread entitled; Refractor Equivalent to an 8″ Reflector.
8″ f/6. You’ll get a little better contrast with an unobstructed scope and imperceptibly brighter image because of light loss on a reflective surface. You won’t have coma on a refractive system, but you won’t have the huge amounts of CA with a Newt that you would have with an 8″ f/6 refractor.
Aperture, aperture, aperture. That’s what matters. A high quality, thermal controlled reflective system will give up very little to a similar size refractor.
Deep 13 (NE Ohio), from an online thread entitled: Refractor Equivalent to an 8″ Reflector.
Recognizing that everyone has their own opinions and preferences, here is my opinion and preference based upon 45 years of telescope ownership which by inventory would include something like about 40+ mounted telescopes and numerous guide scopes that would add about 15 or so more to the mix. I have had all types of scopes including both apo and achro refractors, maksutovs, schmidt-cass, newtonian reflectors (both equatorially mounted and dobsonian). While different telescopes are suited for different purposes, my overall preference is the refractor for a number of reasons, in particular the apo refractor of which I have owned 8 different apos. I also enjoy the classic long focal length achro refractor and have extensive use and ownership experience with Unitron refractors………………From my personal experience and in general for most applications my rule of thumb would be that a Newtonian would have to “out-aperture” a refractor by about 33% to be roughly equivalent for most applications. Accordingly the statement that a 6″ refractor is equivalent to an 8″ reflector is for the most part, pretty valid.
Barry Simon ( New Orleans, LA), from an online thread entitled; Refractor Equivalent to an 8″ Newtonian.
My guess is that a great 5 inch apo refractor would equal an average 8 inch mass produced mirror and it would take a great 6 to 7 inch refractor to equal a great 8 inch reflector. A generic 10 to 12 inch mirror will beat or equal any refractor under 8 inches. These guesses are based on real world observing at most objects. There are always exception.
Wade A. Johnson (North Central Iowa), from an online thread entitled; Refractor Equivalent to an 8″ Newtonian.
I have done the side-by-side during a couple of well attended starparties. My well collimated and optically very good C8 performed extremely similar to a very good Meade 6″ APO on Jup[i]ter on a night of exeptional seeing. The refractor edged it out with better contrast. No surprise. Compared to a home made 8″ Newtonian with a small 20% obstruction the images were almost impossible to tell apart.
So, my answer to the original question is: 6″ refractor.
I think we are finally well past the myth of a 4″ refractor being “sharper” or “showing more” than an 8″ reflector.
Contrailmaker, from an online thread entitled: Refractor Equivalent to an 8″ Reflector.
This old and tired conversation just seems to drag on and on, using the same old arguments that fly in the face of both common sense and physics. Drop it…let’s all agree that a 6″ Apo costing $7000 is a bit better than an 8″ F5.9 reflector costing less than $1000.
Which one would a sane person on a budget buy?
Covey32 (Georgia, USA), from an online thread entitled: Refractor Equivalent to an 8″ Reflector.
I would politely disagree to this. I looked through an excellent 5″ apo (my old Tak TOA-130S) and a very good 8″ Newt (8″ f/7) at Jupiter and Saturn. My Tak was soundly beaten by the views through the 8″ Newt.
Alvin Huey (Greater Sacramento) from an online thread entitled: Refractor Equivalent to an 8″ Reflector.
An 8″ mirror doesn’t have these thermal stability issues that are fundamental to larger apertures. Cool-down is relatively quick as long as you have a pyrex mirror. An 8″ plate glass mirror with a fan will also cool down quickly.
8″ f/8 newts (provided they have a solid/split tube design) can be staggeringly good planetary scopes. Wholly apart from the materials costs of refractor glass, you’re more likely to get a perfectly figured optic than you are with an apo. Refractors have more optical surfaces that have to be accurately figured (4 in a doublet, six in a triplet) whereas a newtonian only has one. At f/8, if using a low-profile focuser, the central obstruction is miniscule and the increase in contrast over a shorter focal length newt can be dramatic. Also, using a single-arc two-vane curved spider like a protostar can go a long way towards minimizing overall diffraction. Also at 8″ or less, the flexure inherent in that design is negligible enough not to affect performance.
Zamboni, from an online thread entitled: OPT 8″ f/9 Planet Pro Dobsonian.
The Astronomers Without Borders’ One Sky Newtonian; an affordable but good quality, ultraportable 130mm f/5 tabletop telescope.
We have 4 scopes that always see some use. A 8″ F8 Newt (Dob mount), a 111mm APO (actually, a lot of 4″ refractors), a 16″ SCT and a 17.5″ F4 Newt (dob). The 8″ has some of the best optics I have ever had the pleasure to use, a true one of a kind scope. Planets are fantastic through it. Actually, pretty much everything is. But, when I want to look at galaxy clusters or similar, the 17.5″ is the scope. When I want to study the details in planetary nebula or small single galaxies, I like the 16″ SCT. On exceptional nights, the 16 is great on the planets too but those nights are far and few between here in the Great Lakes State (only 1 really comes to mind in the last 10 years…).
Jason B, (Michigan, USA), from an online thread entitled: 1 inch Apo vs 12 inch SCT.
Under the stars, this telescope really shines now. It really is nearly the equal of my 10 inch f/6, a ‘scope I have been told by many who look through it, has Zambuto like quality. Planetary detail is excellent. Deep sky is just great. I find myself surprised over and over again by this telescope. The figure on that primary is just excellent. We did not touch what the original guys at Cave Optical did with the figure, we just recoated it. I reviewed this ‘scope on the Todd Gross astro equipment ratings site, and I’ll tell you now what I said then. If you like vintage ‘scopes and you don’t have one of these, try to find one. You won’t be disappointed!
Edward Conley, (North Branch, MI, USA), from an online review of a Classic 8″ f/7 Cave Astrola Newtonian.
FWIW Rolando [i.e. Roland Christen] said the best view he ever had of Saturn was through a 12.5″ Cave – 800x was no problem.
deSitter, from an online thread entitled: Cave Telescope Estimate of Worth.
Jupiter on the morning of October 8 2010 by Jason H ( Central Florida, USA); afocal footage from a Criterion RV 8 f/7 Newtonian reflector.
When I rece[i]ved my 6″ F/8 Criterion RV-6 I was amazed at the detail I could see on Jupiter. Since then I have heard many others say how well their RV-6 scopes performed. Why did these scopes seem to perform so well? How do they compare to “modern”: Newtonians like Zambuto mirrored scopes?
Jim Philips (South Carolina, USA), on an online thread entitled: Criterion RV-6 Dynascope.
Well I always like to have an excuse to repost a picture of my restored 1960 or 61 original RV6. Yes the optics are as good as everyone reports. I agree with what others have written that the 6 inch at f/8 is relatively forgiving and if well made performs excellently even with a spherical curvature. After seeing a neighbors RV6 outperform my Astro Physics 6 inch f/8 triplet,(early model), I sold the refractor and restored my RV6 to almost like new condition.
Bill Nielson (Florida, USA), on an online thread entitled: Criterion RV-6 Dynascope.
Snart, from an online thread entitled 8 inch Newt vs 5 inch Apo.
I just got back from a weekend star party and pretty much had observed the same thing. My well collimated DOB showed more and better than anything that had less aperature. Since I cant afford anything in the APO category, it left me pretty pleased with my equipment…….. VERY encouraging. I guess my homework and the help supplied from CN has led me to the right stuff!
Being a newt guy, I’d agree that an 8″ reflector can beat a 5″ apo refractor. However, I would point out a few things: The newt may require more cooldown time, and it may be more affected by seeing conditions, tube currents, etc. The newt will show diffraction spikes around bright objects unless a curved spider is used, while the refractor will obviously not. The refractor may show a “cleaner” image, but not necessarily more detail. This is especially true if the newtonian has a large central obstruction, isn’t flocked, etc….The great thing about newtonians is that they’re easy to modify. A flocked, collimated, cooled down newt with a curved spider, nice focuser (being perfectly in focus is important on planets!), and good optics will be right on par with an apo refractor of the same aperture minus the secondary obstruction, IMO.
Erik, from an online thread entitled 8 inch Newt vs 5 inch Apo.
like i always show my students; a 6″ unobstructed, perfect optic is creamed in resolution by a 10″ 20% obstruction 1/10 wave newt:
http://www.astromart…?article_id=473 (thanks darren!)
this is why i always wonder when people say refractors are best on planets…..
like i always show my students; a 6″ unobstructed, perfect optic is creamed in resolution by a 10″ 20% obstruction 1/10 wave newt:
That’s fine, Dave but your skirting the issue. I’ve now been painted into the corner. Can you give the nod to a 6 inch
F/8 reflector against a 150mm Tak,AP,TMB,etc,?
if they both cost the same, i would take the 155mm AP.
if the 155mm AP and an 1/8 wave 8″ newt both cost the same, i would of course take the 8″ newt.
dave b, from an online thread entitled 8 inch vs. 5 inch Apo.
When I owned an 8″ Mag1 Portaball with a Zambuto mirror, I used to compare the views of the planets through my telescope with refractors. Over a two year period, there were a few refractors that came close to providing better views on a few exceptional nights, but I didn’t find a refractor that could compete head-to-head with my reflector. (The best refractor, the one that came the closest, was an AP 155, if I recall correctly.)
I now own a 12.5″ Mag1 Portaball (also with Zambuto mirror.) I’m still waiting for the night where the refractors demonstrate their clear superiority. I’m not holding my breath. Under crappy seeing conditions, I’ve seen the phenomena of a refractor providing what its owner called ‘a more aesthetically pleasing view.’ This is another way of saying when the seeing is bad, smaller aperture scopes don’t see the bad seeing as well as [a] large aperture scope. (In this type of condition, one can ‘stop down’ the larger scope and see the same sort of views that are seen by the refractor.)
When the seeing is good to excellent and when optical quality is excellent, aperture wins every single time. And dollar for dollar, high quality reflectors rule.
But don’t take my word for it. Check out Gary Seronik’s article “Four Infamous Telescope Myths” in the February 2002 issue of Sky and Telescope. You can also go to star parties and try a few experiments. Under good seeing conditions, take a look at the planetary views through a correctly collimated reflector equipped with a Zambuto, Royce, Swayze, Hall, etc. mirror. Then take a look at the views through a 6″ refractor that’s many times more expensive. I think that the results might surprise you.
Finally, consider this Mars image, made by Wes Higgins with a 14.5″ Starmaster. In the past, when the optics in most large reflectors were mediocre at best, I believe that high quality refractors provided the best views. Now, with high quality optics readily available in large reflectors, I believe the situation has changed.
Barry Fernelius, from an online thread entitled, Reflector versus refractor.
What more and more people are doing right now in France, is to buy those chinese 8″ or 10″ f/5 or f/6 Newtonians, play with them for some time, then have the primary mirror refigured to an exceptional quality for around €1,000 (US$ 1,250) with enhanced reflective coatings. They perhaps add a better focuser and tweak the spider a little bit. After that treatment on a 8″ reflector with 20% central obstruction, a 6″ APO can no longer match it for visual work.
Rhadamantys, from an online thread entitled, Reflector versus refractor.
At the risk of beating a dead horse, my experience is that an APO refractor delivers consistently a[e]sthetically pleasing results every time, with detail limited only by atmospheric conditions and aperture. A high-quality, well designed newt can also deliver [a]esthetically pleasing views, with detail limited only by atmospheric conditions and aperture. Everything else being equal, quality aperture wins, every time. Not surprising that (last time I checked anyway) Thomas Back’s personal scope for planetary viewing is….wait for it…. a 20″ Starmaster. Nuff said?
Gary in Ontario, from an online thread entitled, Reflector versus refractor.
A 130 mm F/5 with a decent mirror and a 2 inch focuser. No CA, much faster than the Mak or the refractor for EAA and very rugged.
I’ve owned several.. It’s scary sometimes how good they can be. I remember one night under dark skies.. I was doing the low power, wide field thing with my NP-101 and swapped it out for a 130 mm, F/5 Newtonian with the 31 mm Nagler and a paracorr. I wasn’t giving up much with the $200 scope.
Jon Isaac(San Diego, California), from an online thread entitled: 4″ refractor vs. 4″ Mak.
As John Browning was to argue in his ‘Plea for Reflectors’ in 1867, good silver-on-glass reflectors had tubes about half as long as those of refractors of similar aperture, they had a superior resolving power when used on dim double stars or planetary surfaces and often gave crisper star images, while unlike large aperture refractors, they were not ‘beyond the reach of all but wealthy persons’.
Allan Chapman, The Victorian Amateur Astronomer, pp 230, (1998).
James Francis Tennant, for example, had used a Browning mounted With 9 inch (silver–on–glass mirror) to observe the Indian eclipse of 1868, while in 1872 Joseph Norman Lockyer had one which produced ‘exquisite definition’. The With instrument in the Temple Observatory at Rugby School and one in a privately owned observatory in Sydney, Australia, were found superior to Clark and Merz refractors of similar aperture. By 1890, With’s mirrors were in use in Europe, Canada, Australia, Asia and elsewhere.
Allan Chapman, The Victorian Amateur Astronomer, pp 232–233, (1998).
I find that the ideal planetary telescope is the largest quality aperture that you will use frequently. It can be fast or slow, in terms of f/#, so long as the optics are good. Ideally the primary is not too thick so it can cool and be cooled in a reasonable time. Proper mirror support and achieving and holding collimation are also very important.
Mike Lockwood (Philo, Illinois), from an online thread entitled: Help me pick a larger planetary scope.
I think that the ideal set up would be a 10″ F/7 Newtonian reflector on a GEM.
Stephen Kennedy (California), from an online thread entitled:Help me pick a larger planetary scope.
My best planet views came from all of my Zambuto and OMI 11 to 18″ mirrors and all were F/5 or faster. On the smaller size mirrors i like slower speeds in the 10″ and smaller sizes.
I am just not a APO fan in sizes over 4″. 3 and 4″ APO’s are my fav all around small scopes. Once you get into the 5″ and bigger sizes cost become a problem for me and 7″ and bigger the mount needed becomes pricey and big. A bigger Newt is many times cheaper and does what i need it to do. No 7″ or 8″ APO would give me the image at 1100x+ like my 14.5″ and 15″ Zambuto and OMI optics have done time and time again.
I have owned a 1/2 dozen garden variety XT6/XT8 Dobs over the last 25 years. None of them were anything special, but they were consistently OK. I also simultaneously owned a sensibly perfect 4” APO and a custom 8” Dob with Zambuto optics.
The 6”f8 Dob consistently gave me better views of all objects than the 4” APO. The 8”f6 Dob consistently gave better views of all objects than the 6”f8 Dob. The 2” difference wasn’t a “wow,” but it was obvious.
The custom 8” Zambuto equipped Dob gave marginally better views than the 8” Synta Dob in excellent seeing, but the difference in the views was much more subtle than the difference that comes with 2” of extra aperture, which is why I would expect a typical, garden variety 10” Dob would probably give better views of anything than a sensibly perfect 8” Dob and cost much less
For reference, a complete XT10 costs $600 and is available off the shelf. An 8” Zambuto mirror starts at $1,100 with an 11 month lead time. A Zambuto equipped 8” Teeter starts around $3,300 with a 4 month lead time.
gwlee (California), from an online thread entitled: Premium mirror versus Chinese mirror.
Beyond that, the main thing is to get out there and use it. I don’t really worry much about whether a premium 8 inch would out perform my GSO 10 inch because the 10 inch does a reasonable job of doing what I ask of it. I do know that I have been able to split double stars with it that are beyond the Dawes limit for an 8 inch. Some pretty awesome planetary views at 410x.. And deep space.
Jon Isaac (San Diego, California), from an online thread entitled; Premium mirror versus Chinese mirror.
I have enjoyed Sky Watchers scopes for 10 years now in almost every circumstance, under light polluted or super dark skies, under ugly or really good seeing, side by side to terrible scopes or world class (Astrophysics) refractors, close the newbies or really experienced observers. They have never disappointed me, when conditions allow, they deliver terrific planetary and deep skies images.
Javier (Buenos Aires, Argentina), from an online thread entitled: Premium mirror versus Chinese mirror.
I had a 120 mm Orion Eon for two years. This is a 120mm F/7.5 FPL-53 doublet and probably better optically than your 120mm Binocular Telescope. I recently sold it because my generic 10 inch GSO Dob was the better all around performer and not just by a little. The Dob was better on the planets, it splits doubles not even worth looking at in the refractor. Globulars, nebulae, galaxies, for deep sky it’s a break through experience.
Jon Isaac(San Diego, California) from an online thread entitled: 10″ Newtonian to upgrate an ED 120.
After having large aperture Newtonians and Refractors, I would say yes, it’s possible to make a Newtonian as good as a a Mid priced apo. My current(and final) scope, a 6″F8 newtonian provides refractor like images of the planets and double stars. Everything snaps into focus and looks as good as in my former 4 and 5 inch apos. At this point in my life, an arthritic back and knees prevent me from owning anything larger and I like the convenience of a dobsonian mounting. I’ve always said that if I could have only one scope, it would be a 6″f8 reflector. It’s an outstanding performer and an excellent compromise between aperture and focal length!!
Barbie, from an online thread entitled; How hard is it to make a reflector as good as mid-price ED or Apo refractor?
The advantage of a reflector is that it scales to a larger size much more affordably; at small sizes that advantage is much less. That is why you see small refractors and large reflectors. The notion that a 4-5″ reflector should be the same price as a 10-12″ reflector, though, is an unrealistic expectation. Next to a 12″ dob, a 127mm refractor looks like a kids toy… they are totally different leagues. Make no doubt about it, a 12″ premium dob will blow a 127mm refractor out of the water in every category except wide field views and ease of use.
dgoldb, from an online thread entitled: How hard is it to make a reflector as good as mid-price ED or Apo refractor?
As Danny shows, the real world can be tamed a little or a lot. Cooling and boundary layers, collimation, and a few other variables are within our ability to minimize. In the tropics the real world is, at times, almost “lab like” with very good seeing and modest temperature differentials. So, even though we cannot talk about performance in isolation, we have a measure of control over “real world” performance except for seeing mostly. We can give our ‘poor’ scopes a fighting chance to perform better than they are often assumed to perform…in the real world, of course.
Asbytec(Norme)(Pampanga, Philliippines), from an online thread entitled, Premium mirror versus Chinese mirror.
I agree with Norme, often performance is all about location, location, location! What works well in the south, or out west might not be the ideal scope for the NE or other locations. You have to tailor your scope to your location and observing goals/habits to get the best consistent experience. There is no such thing as the perfect scope for any location, observing style etc. If there was we would all have it.
Richard Whalen (Florida), from an online thread entitled, Premium mirror versus Chinese mirror.
I have a superb TEC200ED and equally superb (optically, mechanically and coolingly…did I just make up a word?) Parallax/Zambuto 11″ F 7 Newt. Other than image brightness and a slight warmth in the TEC’s color tone, there is little difference between them for solar system viewing. Sometimes I prefer the TEC, others the Newt. The only “glaring” difference is the Newt’s diffraction spikes, especially on Jupiter and Mars. But I’ve learned to live with the spikes and ignore them much like I can ignore CA in achromats ( if it’s not too severe anyway), however there are also solutions for that too.
For me, the key to really enjoying my newts has been great optics & great mechanical and cooling designs. I want my newts to behave like an excellent APO and I’ve found that it is easily done if I pay attention to the big three: optical quality, mechanical design & execution, and cooling design & execution. Everything else is “sauce for the goose” for me (however, I freely admit to being one of those people who have sub-F5-phobia and yes, I am considering seeking therapy for it).
Jeff B, from an online thread entitled: How hard is it to make a reflector as good as mid-price ED or Apo refractor?
I have one mount and two great scopes-an APO and a reflector. I usually go a month or so with one and then a month or so with the other.
After a month with the reflector I’ll switch to the refractor and notice how pretty the stars look all across the field.
After a month with the refractor I’ll switch to the reflector and achieve higher mag than is possible with the APO.
I’m not sure I could call one a favorite but I like the refractor for any outreach situation. It just seems easier for the uninitiated.
Steve O (Wichita, Kansas), from an online thread entitled: How hard is it to make a reflector as good as mid-price ED or Apo refractor?
I had a mid 1960’s vintage Cave Astrola Deluxe 10″F7 reflector and a GSO 10′ F5 dob and they both showed the same amount of detail on the planets. The ONLY difference was that the GSO showed a little coma whereas the Cave operating at F7 didn’t. They were both outstanding scopes and any differences other than the above noted were essentially splitting hairs. It is quite possible to get a Chinese optic that is outstanding. My current 6″f8 is a testament to this fact. I think over the last 15 or 20 years, the quality control has gotten a lot better and the chances of getting a lemon are far less but I’m sure the occasional one still gets through.
Barbie, from an online thread entitled: Premium mirror versus Chinese mirror.
I have also found that it’s much easier to find and purchase sensibly perfect (SP) refractors off the shelf than SP reflectors, which are usually only available from a few small custom shops. Custom SP reflectors are very expensive compared to off the shelf scopes. They have longer lead times, and some sizes, 6”f8 for example, are not available.
Why? I believe that most people are satisfied with the optics and mechanics of production reflectors at 1/10 the cost and don’t want to wait months for delivery, so the market for SP reflectors too small to be attractive to large manufacturers who stay in business by selling people what they want to buy at a price they are willing to pay and do it efficiently enough to make money.
For example, my factory 8”f6 Dob cost me $300 and was delivered to my front door by a big brown truck within 48 hours of placing my order. My custom 8”f6 reflector with sensibly perfect optics cost me $3,000 and delivery took a year. Its optics were better, but the improvement was subtle, usually requiring side-by-side testing in better than average seeing to confirm.
On the other hand, the optical improvements to be had from a 10” factory reflector costing $600 are immediately obvious, so more people are inclined to upsize their reflective optics rather than upgrade them. Other people who are basically satisfied with their mass produced factory reflector optics might prefer to spend the same $3K on a SP refractor, not because it’s better than a reflector, but because it complements a reflector so well, it’s available off the shelf, and it scratches the SP itch too.
gwlee (California), from an online thread entitled: How hard is it to make a reflector as good as mid price ED or Apo refractor.
My personal experience has been that my dirt-cheap 10″ GSO Dob produces better planetary images than my 4″ Apo that cost well over 10 times the price. Yes there is some diffraction, but the increased resolution, brightness and higher possible magnification compensate for this.
There is definitely a point where a good reflector (probably Newtonian) must overtake any practical Apo (i.e. <=6″ for most mortals). I suspect this point is probably achieved with premium reflectors >9″-10″ aperture.
JohnGWheeler, (Sydney, Australia), from an online thread entitled: How hard is it to make a reflector as good as mid price ED or Apo refractor.
As of last night I now have some direct experience relevant to the question at hand . . .
A seller had got together the parts to build an 8″ F7, had sold it to a second guy who was more of an imager and decided not to go ahead with the build. I was the third in line, and I finally got it put together.
Parts are an 8″ F7 Zambuto quartz mirror (made in 2016), a 1.3″ 1/30th wave astrosystems secondary with holder and four vane spider, 10″ x 60″ parallax instruments tube, and a moonlite single speed focuser. It also came with a Meade cell that I upgraded to a Aurora precision cell, and I had to get flocking, rings (parallax), and a dovetail plate.
After two days of drilling, filing, screwing, sticking, and flocking (and probably several other ‘ings’) I now have a fan-bleeding-tastic 8″ F7 Newtonian for something in the neighborhood of $1600.
I made mistakes along the way. I miscalculated the placement of the spider/secondary, and so had to source a longer bolt for the secondary. I got lucky with some old plumbing parts that serve as a ball joint at the end to pivot the mirror for collimation. I messed up a measurement on locating a hole for the spider, and my flocking job doesn’t look completely pretty, but it works.
First light was yesterday afternoon on the moon. Seeing was so-so. High frequency fuzz that makes it seem that the focus is always out interspersed with brief moments of stability. Jupiter finally got high enough for a look around 10:30 PM . . . poor to moderate seeing, but WOW! Exactly what you’d expect from these optics. GRS was bang in the middle of the planet, and very obviously off-pink colored. Numerous bands and a big blue barge visible. Brief moments of very good seeing and I was up to ~300x.
So how does it compare . . . well, it blows my Televue 101 out of the water on Jupiter and the moon. In fact, it blows my old 6″ F8 triplet apo out of the water, and provides nicer contrast by far than I ever saw in my 11″ Edgehd, albeit with less illumination. And compared with my 12.5″ F5 (Zambuto again) Portaball, well not quite as good as that, but the Portaball would still be thinking about cooling when the 8″ was throwing up great views.
areyoukiddingme (Santa Barbara, California), from an online thread entitled: How hard is it to make a reflector as good as mid price ED or Apo refractor.
Bigger Newts will always beat out smaller APO’s on cost and image detail on planets if they are built good. Now compare a 8″ APO to a 8″ Newt and the APO is gonna win, but at 20 to 30 times the cost of the Newt.
CHASLX200(Tampa, Florida); from an online thread entitled; SW MAK 180.
Others will advise a moderate-sized reflector as affording wonderfully fine views of the Moon and planets. The question of cost is greatly in favour of the latter construction, and, all things considered, it may claim an unquestionable advantage. A man who has decided to spend a small sum for the purpose not merely of gratifying his curiosity but of doing really serviceable work, must adopt the reflector, because refractors of, say, 5 inches and upwards are far too costly, and become enormously expensive as the diameter increases. This is not the case with reflectors; which come within the reach of all, and may indeed be constructed by the observer himself with a little patience and ingenuity.
*My 10-inch reflector by With-Browning was persistently used for four years without being resilvered or once getting out of adjustment.
William F. Denning, Telescopic Work for Starlight Evenings (1891) pp 38-39
An amateur who really wants a competent instrument, and has to consider cost, will do well to purchase a Newtonian reflector. A 4 1/2-inch refractor will cost about as much as a 10-inch reflector, but, as a working tool, the latter will possess a great advantage. A small refractor, if a good one, will do wonders, and is a very handy appliance, but it will not have sufficient grasp of light for it to be thoroughly serviceable on faint objects. Anyone hesitating in his choice should look at the cluster about χ Persei through instruments such as alluded to, and he will be astonished at the vast difference in favour of the reflector….. When high magnifications are employed on a refractor of small aperture, the images of planets become very faint and dusky, so that details are lost.
William F. Denning, Telescopic Work for Starlight Evenings (1891) pp 41-42
Perhaps it may be advisable here to add a word of caution to observers not to be hastily drawn to believe the spots are visible in very small glasses. Accounts are sometimes published of very dark and definite markings seen with only 2 or 3 inches aperture. Such assertions are usually unreliable. Could the authors of such statements survey the planet through a good 10- or 12-inch telescope, they would see at once they had been deceived. Some years ago I made a number of observations of Venus with 2-, 3- and 41/2 inch refractors and 4- and 10-inch reflectors, and could readily detect with the small instruments what certainly appeared to be spots of a pronounced nature, but on appealing to the 10-inch reflector, in which the view became immensely improved, the spots quite disappeared, and there remained scarcely more than a suspicion of the faint condensations which usually constitute the only visible markings on the surface.
Concerning Venus: William F. Denning, Telescopic Work for Starlight Evenings (1891), pp 151
Coma is essentially negligible at F/8. It’s there, and can be seen in my 2″ widefield eyepieces, but it’s very muted, even compared to my F/6.24 8″ GSO, to say nothing of the multitude of F/5 and faster mirrors out there. The SkyWatcher 6″ traditional dobsonian makes a nice lightweight alternative when I want something quick to setup, but with enough aperture to wow people on the planets and such. The SW6 makes owning a 5″ refractor obsolete, in my opinion, all while providing the great dobsonian stability that handles the West Texas winds so much better than anybody’s refractor that’s not in an observatory, or using a mount that’s ridiculously heavy and expensive (to say nothing of the accompanying 120mm+ ED glass tube). Yes, it will have less thermal stability, like all reflectors compared to refractors, but that’s a problem one might resolve with a cross-mirror fan, and would be a whole lot cheaper to implement than a big mount, ED glass, etc, without affecting general portability very much.
I like reflectors, and especially dobsonians, for their ease of setup and use. I have always preferred the eyepiece-at-the-top-&-angled kind of design ergonomically, and the general dobsonian design, with the weight at the bottom of the tube, cannot be emphasized enough how wind resistant it is compared to a refractor’s flying in the air like a flag setup. This comparative difference was demonstrated to me Saturday night, when I had out my SW6″ for its maiden sky-voyage and an often-used Kunming 102mm F/7 refractor on the GSO SkyView Deluxe Alt-Az mount. Although it wasn’t very windy that evening, we still had some, and every wind produced a light dance in the refractor, and only a little wiggle in the dobsonian, which dissipated much, much more quickly than the spasmodic gyrations of the image in the refractor.
I will have to decide if I want to sell my most excellent Z8 and replace it with a GSO-10″-dob-and-Coma-Corrector or not. That’s a different story, and would involve comparing dobsonian performance to 6″+plus refractors, which are, to my line of thinking, insane and off the table, cost and mount options considered. But I believe the stories I’ve read here on CN, that a 6″ reflector can keep up, visually, with 5″ ED refractors. I’ve seen for myself how much better Saturn appeared one evening long, long ago, in a LB8″ dob compared to an Orion 120mm ED scope. No comparison, really, the 8″-er was that much better, so I’m sure one would have to move into the refractor stratosphere to continue competing with dobsonians above 6″, and why I’d never own such a refractor. But the SW6, especially if I can upgrade the rather inferior Synta 2″ rack and pinion it comes with, puts all the performance of a 120-127mm refractor into an easier to manage, more stable package, at a fraction of the cost.
CollinofAlabama (Texas, USA), from an online thread entitled; Of coma & 120mm ED refractor.
The best telescopes known to amateur astronomers have a thin aluminum coating supported by glass, diameters considerably exceeding the largest apochromats, and are at their best under dark, steady skies.
Alan French (Upstate New York, USA), from an online thread entitled, Comparing FPL-53 and CaF2
It is worth remembering that Stanley Williams and Elmer J. Reese, whose names stand very high in the list of students of the planets, did most of the work for which they are remembered with reflectors of less than 20cm aperture. One of the authors(W.S), while at home from college in March 1978, made an independent discovery of a new SEB disturbance with a 20cm reflector. There was nothing extraordinary in the feat; it was simply a matter of looking at the right time and knowing enough to recognize the significance of what was seen.
William Sheehan & Thomas Hockey, Jupiter, Reaktion Books, 2018, pp 161
Well after sitting in my living room corner for several weeks after purchase I managed to get out last night with an Orion XT6 dob, now this is the basic one, 1.25″ focuser, no eyepiece rack and just the one eyepiece, lots of eyepieces already so its not needed anyway. I bought this on a whim new for less than what I have paid for a mid range single eyepiece, $300 Canadian taxes included, free shipping. I,m older and weight was an issue so the 6″ made more sense than the 8″ which I owned many years ago so I was aware of the weight and bulk of it, also the 6″ will live in a small upright tool shed I have for gardening stuff. Just lift it out and use it.
Lots of light pollution where I live so I tend to observe the moon and planets so after adjusting the secondary (it was way too far towards the primary) I turned it onto the moon.
Well it looks like I got a good one and I came in at 1:30 pm when both it and Jupiter fell behind the trees, tremendous detail on the moon and sharp crisp views, I like a lot of others have over the years got wrapped up in complex and expensive gear so have a night like this for a modest outlay was a delight, I found it really worked well with some of my lower cost eyepieces, higher grade ones made a difference but not that much.
Binojunky, from an online thread entitled Cheap small Dob Delight.
The XT6i was my default recommendation to newcomers who were confident they would enjoy the hobby. Alas, Orion no longer offers the 6″ with IntelliScope. As Binojunky said, enough aperture to open the door to DSO, can handle magnifications I like to use on planets (200x-300x), light, easily carried, etc., etc. It’s also the perfect size for kids who are old enough to “drive” by themselves. My son and I used one when he was ten. He liked that he could collimate it himself, use the IntelliScope computer himself and point the scope himself. He just wished it tracked.
macdonjh, from an online thread entitled Cheap small Dob Delight.
I have owned three of each and still have one of each, both Orion. 6”f8 weighs 34#. 8”f6 weighs 41#. 7# doesn’t sound like much, but it’s a major difference for me at this site that requires a lot of tree dodging; 6” is very easy to use here; 8” is almost unusable, which is why I own the 6. Be aware that 6 and 8 weigh about the same with some brands, SW for example.
Focal lengths are identical, 1,200mm. 6s cools a little faster. All three 6s had a poor a quality 1.25” focuser. It can be adjusted well enough to be serviceable, but requires frequent tuneups. 8s come with an OK 2” focuser. Both are equally easy to colimate to the required tolerances using laser or collimation cap; theory suggests the collimation tolerances are more forgiving on the 6”, but I haven’t noticed a practical difference.
Optical quality (figure) of all of them were about equal, good to very good, no advantage to 6 or 8. 6” might be easier on inexpensive eyepieces, but I only use expensive EP, so can’t say from experience, but it’s consistent with optical theory.
With the same LP EP in both scopes, the 6” has a smaller exit pupil, which is a bit more compatible with the astigmatism in my eyes, so star fields seem a bit sharper to me. At the same exit pupil stars are equal[ly]sharp to me in both scopes. I doubt a person without astigmatic eyes would notice a difference.
The larger 8” is a noticeably better optical performer an all targets, but especially DSOs. Noticeable, but not wow! I also believe the 8s have slightly better motions, but it’s subtle, and most people probably won’t notice the difference if they don’t have the opportunity to use bith scopes side-by-side. For sites where I can carry the scope out in two pieces and leave it in one place all night, I prefer the 8.
gwlee(California), from an online thread entitled Cheap small Dob Delight.
I was quite lucky when I bought my 6″F8 Synta(Orion) xt6. Its optics are so good that I don’t really need a premium mirror maker to make me anything better since my Xt6 shows a textbook star test and has been lab tested to be of excellent quality. Perhaps the Chinese have really gotten the 6″F8 optics to a very high level of performance and Zambuto knows this which is why he doesn’t make anything smaller than an 8″. Perhaps not, I don’t know for sure but all I can say is that my 6″f8 shows me fantastic views of the planets rivaling those of my apo refractor [100mm f/9 ED], but with a little more light grasp for deep sky objects. About 20 years ago, I had a Bushnell 6″F8 Dob and it was just o.k. Fast forward to the present and my current 6″F8 dob, the difference is like night and day in optical performance and mechanics so I would say the Chinese have improved by “light-years”, at least when it comes to making 6″F8 mirrors.
Barbie; from an inline thread entitled;Why won’t Zambuto make 6″ f/8 mirrors.Truth Please
Did a public star gaze on the beach last Friday and Sat night. Took my 6 inch f8 home built dob out there.
Haven’t done any such gazes in years and back when I did I was hauling out the 10 f5.6 “big dob”.
Turns out the 6 inch f 8 is the perfect outreach scope as well !
There was a C8 celestron. A 9.25 something or other cat. A 4 inch relatively fast ED refractor. Some other guy with another C8 ish type scope set up with a display screen and astrophotography.
Then, off to one side was my little 6 inch F8 Dob.
A fair fraction of the folks that looked through my scope made a point of saying that they were attracted to the scope and wanted to check it out.
And I can think of several reasons why. First obviously home built. Not nearly as impossing as the other scopes. Even the 4 inch frac had a serious looking mount. Not complicated looking. Those other scopes with all those fiddly bits and hand controllers and whirling motors are fairly intimidating to the general public I think. And needless to say the astrophoto/display screen scope took that to the next level.
Not only did it look simple…folks could see it was simple in use. Look at Jupiter say. Then swing around, sight along the side of the tube or use the laser pointer on the tube and bammmm….now we have Saturn….swing around again….Venus….swing around again…Alberio…swing around again…the moon…and so on and so on.
Need to move the scope to get an unobstructed view of X? Pick it up….move over…plop it back down….bam….done.
Most people expressed awe that I could “just find” things. But I explained things…simple landmarks in the sky. Albierio….end star of the easy to see Cygnus. M4…sorta between Antares and that other star. M22…forms a parallelogram with the handle and top of Scorpious the Tea Pot. M57….right between those two easy to find stars near easy to find Vega. Explained how Mars, Jupiter, and Venus are fairly obvious targets once you know what you are looking for. And even Saturn with a little care.
Then a fair number got fairly interested in the home built aspect. Hey, I just bought the optics and built a wooden box ! The side bearings are PCV flanges…look here the focuser is made of plumbing parts….you can do this too…especially with all the info and help on the internet these day….
Hey, how much does this cost? Ohhh, you can get something like this for around $300. A bit more and you can get an 8 incher ! The 4 inch frac cost about twice that (the tripod alone was $300). The other scope…well, more like $3000 rather than $300. They probably didn’t wanna know what the imager guy had invested.
As for views? The 9.25 showed a little bit more detail on Jupiter…but it was all a bit washed out to me (probably that large secondary mirror doing that). The six f/8 dob beat everything else IMO. And this is just some random mirror I bought 25 years ago with a bog standard diagonal. Have never even star tested it. And the eyepieces….my $10 Vite 3 element/plastic lens 10 and 23mm plossls.
End of the night. Put the tube under one arm…grab the handle on the rocker box and walk to the car in the parking lot. Easy peasy.
I think a lot of people came away less intimidated about telescopes and costs and finding things in the night sky after seeing the little dob in action.
Starcanoe; from an online thread entitled; Cheap small Dob delight.
I built and enjoyed this 6-inch F/7.3 before I even knew what a Dobsonian was. But it’s really close to that concept. Enjoyed that for a long time, added setting circles and wroth my own calculator program to point at things. Used that for years on planets, clusters, nebulae, etc. It was wonderful! I would take it in my compact car to star parties. Very convenient. Sure, I eventually went bigger… but your point is a good one. There is a LOT to be said for starting out with this size and doing visual.
TOMDEY( Springater, New York, USA): from an online article entitled: Versatility of a 6″ Newt.
A 6″ f/8 holds a special place in the hearts of us older amateurs. The classic RV-6 Criterion is the poster child for the 6″ f/8s. Many had exquisite optics and the planetary views were quite memorable. I was interfaced with an RV-6 in high school (I graduated in 1970) – the school owned one and it was superb.
Yeah – yeah, that’s the nostalgia talking.
Today, with the Dobs, I would say that the modern equivalent is the 8″ f/6. It’s not that 6″ f/8 is any less worthy a telescope than it was 50 years ago – it is still a wonderful telescope to own. But nowadays the 8″ f/6 has such a small differential in price to the 6″ f/8 that it makes sense to get that instead for most folks. Both telescopes share the same 48″ focal length. So both are manageable as far as size is concerned.
Siriusandthepup(Central Texas, USA): from an online article entitled: Versatility of a 6″ Newt.
I agree with siriusandthepup that while a 6-inch f/8 Dob is a great scope for beginners — and for experienced observers as well — an 8-inch f/6 Dob is even better. The 8-incher is very nearly the same size as the 6-incher due to its shorter focal ratio, and is quite a bit more capable. The only real advantages of the 6-incher are that it’s somewhat lighter and cheaper and significantly more forgiving of poor collimation. But once you learn how to do it, collimating an f/6 scope should take well under a minute in most cases.
As it happens, my own scope is halfway in between — a 7-inch f/5.4 Dob. It’s a total joy to use, in every way. I can carry it easily in a single trip and set it up in a matter of seconds. Its ergonomics are miraculous — completely stress-free observing while sitting in a standard chair for objects almost from the zenith down to 20 degrees above the horizon. With a 2-inch focuser, it has an amazing widefield capability, fitting and framing objects like the Pleiades beautifully.
On 90% of all nights it shows almost as much planetary detail as my 12.5-inch Dob. Under dark skies, it shows hundreds of deep-sky objects with ease, resolves at least a dozen globular clusters, and shows a great deal of detail in nearby spiral galaxies such as M33, M51, and M101.
Tony Flanders (Cambridge, MA, USA): from an online thread entitled: Versatility of a 6″ Newt.
I have been using a celestron c102 4″ f/10 refractor for weeknight hour-long observing outings. With the planets well placed they have been getting much more time lately. However, I find the CA quite bothersome (perhaps spoilt with my other scopes Nexstar 8 GPS and 12 inch dob – naturally color-free but more cumbersome to set up than the 4 inch frac).
I have been eyeing the At102ed as the natural solution to my problem, and a while back was able to compare the views between the two scopes. Another person present at the club outing had a 6-inch f5 reflector with 2 inch focuser and type 1 paracorr.
The reflector provided best views of saturn and jupiter – bright, sharp and color-free. It was slightly better on globs like M13 (obviously due to the slightly better light grasp). With the paracorr it was also an amazing wide-field instrument. Just a slight step behind the At102 in FOV department, the paracorr-corrected views were brighter and more engaging to me than the At102ed. It displayed all the portability advantages of At102ed, had better color correction, and provided slightly better wide-field performance but with a slightly smaller wide-field FOV.
Going by memory (as I had not set up the C8 side-by-side that night) I’d rate the views of the 6″ reflector far closer to the C8 than to 4″ refractor.
I was about to pull the trigger on At102ed, but I found the 6 inch f5 more satisfying. Although a 4″ ed better compliments my existing line-up, the 6″ f5 is a better stand-alone scope.
eklf (Carrboro, North Carolina, USA) from an online thread entitled: Versatility of a 6″ Newt.
I am all about aperture most of the time.That being said, my 6″ is a keeperI have seen spiral arms of M51 in it and fanstastic planetary observing as well. Under dark skies it is a very capablle little scope.Even after getting a 15″ I have sometimes used it for conveniece or neccesity and it has not been ” too bad I can’t use the 15″ scenario.It satisfies.Easy forgiving collimation, very quick cool down and super easy to transport.Odds are you will have good to great optics as well. Outside of Quasars it shows all of the types of objects out there.
aatt (Connecticut, USA), form an online thread entitled: Versatility of a 6″ Newt.
Definite pros and cons to different sizes. Mass produced costs less, though. With 8″ f6 vs 10″ f5, both should be moved in 2 pieces. But the 8″ can moved in one piece if you really need to dodge a tree. Still, you will want more aperture.
6″ is enough to get interesting views. M13 starts to break up. Planets start to get beef that the 4″ can’t muster. The view is wider. And the scope is portable. But 6″ is mainly a grab n go. If you drive way out some place dark, you will want a 10″ to enjoy the night. Even at home, the 10″ will be much better on planets.
Stargazer193857(Southern Idaho, USA), from an online thread entitled: Versatility of a 6″ Newt.
Webster telescopes has a 14.5″ f4.5 with a Zambuto mirror, you can upgrade to a quartz mirror for even better planetary views. I’ll bet with the Zambuto quartz mirror it would give better planetary views in good seeing than the TOA 150. Deep sky objects would be no contest.
Astro-Master: from an online thread entitled, Visual Only: 150mm Triplet APO vs 14″ Dobsonian
I would vote the 14 as well (if it is a good mirror), but the Tak may be the nicer built scope (definitely more pricey). With the budget of the 150, you could easily get a top quality premium primary and secondary mirror set and dominate the optical performance of the 150 (16″ or 14.5″ Zambuto/Lockwood/Lightholder/etc(other good makers). with 1/30 wave antares secondary, feathertouch focuser, cooling fans, etc. etc.). With the budget of a TOA 150, you could get a TSA 120, TOA 130, or TEC 140 and a nice quality dob.
To strictly answer your question and assuming the mirrors in the obsession are good,
On a good night with good seeing, both scopes will perform well. Coma will dominate the edge of the field in the dob unless it is corrected with a coma corrector.The Tak will be a easier to set up. The obession will take longer to cool down (especially true if it is a 2″ thick mirror). The 14″ will need to be collimated accurately before every use (recommend a good collimator like Glatter laser and Tublug barlow attachment). Stars may appear sharper in the TOA 150 (I have never used one, but I would expect this result), but you will see a ton more stars and even fainter stuff in the 14. The 14 will also have more resolving power to split tight doubles, and the 14 will be able to handle more magnification on planets. If the seeing is not as good, the TOA may perform better on planets with a sharper image. Also the TOA should cool much faster. I would expect the image to break down faster at high magnifications with the TOA than with a well collimated and cooled 14″ dob.
If you want to do any photography, TOA no question. For visual only, it depends on the circumstances, but I would take the 14.
Jakecru (Nevada, USA): from an online thread entitled,Visual Only: 150mm Triplet APO vs 14″ Dobsonian
To me a Dob and apo are complementary scopes, as each is better at different things. The Dob will go a lot deeper, and will be much better for most deep sky objects IMO. Definitely the scope of choice for globular clusters, planetary nebulae and galaxies (except perhaps Andromeda). The apo will have a wider field of view, and will be generally better for larger extended objects, and rich field observing. The apo will generally yield more aesthetically pleasing views of stars. On planets the apo will give a pleasing view unless the seeing is bad. The Dob potentially has more of an upside on planets but a lot of things have to go right for it to give nice planetary views, including good thermal control and good collimation.
turtle86, from an online thread entitled: Visual Only: 150mm Triplet APO vs 14″ Dobsonian.
Get the large dob + a 4 or 5″ refractor for wide field.
AxelB( QC, Canada), from an online thread entitled: Visual Only: 150mm Triplet APO vs 14″ Dobsonian.
Not just brighter, but far more detailed. I’ve had views of planets through large Newtonians, notably Mars and Jupiter, under exceptional seeing that can simply not be duplicated through any 150mm apochromat.
Alan French, (Upstate New York, USA); from an online thread entitled; Visual Only: 150mm Triplet APO vs 14″ Dobsonian.
I think we have to be careful with generalizations when commenting on APOs vs. Reflectors.
While I generally agree with what is being said we need to be careful to separate the subjective from the objective and also ensure we are comparing instruments of comparable quality / cost irrespective of design.
Subjectively, yes you could say the view in an ED apo is better but objectively a 14″ will have significantly higher light grasp, resolution and contrast vs. a 6″. There is just no competition.
On my second point….
My 14″ has a high strehl mirror and a 19% obstruction secondary. It costed me the same as a premium 6″ APO (but still much cheaper on a $ / aperture basis). With the coma corrector the views it produces are just sublime – pinpoint stars and no coma anywhere in the fov even with my 82deg 30mm. The airy disk is so tight it is almost indistinguishable from an apo.
In excellent seeing I can see festoons within festoons on Jupiter and swirling clouds within the GRS – views that are unmatched by any 6″ apo. I doubt even a 8-10″ apo will come close.
But I still use my 4″ and 5″ refactors and my C9.25 more simply because they are “easier” given my limited time. The 14″ comes out on the weekends or on dark site trips. To me the refactors have a completely different value proposition.
Astrojedi(Southern California, USA); from an online thread entitled: Visual Only: 150mm Triplet APO vs 14″ Dobsonian.
I’ve previously reported running my TOA150 up against Cotts’ 12″ with Lockwood optics.
On large structures – say like the Pleiades or other things bigger than a degree across and maybe the moon, the Tak wins. On everything else, the Dob wins easily.
If you want to shoot images, the Tak wins on everything (but you don’t want to shoot images.)
If you want to put it in your car, it’s roughly a draw – the Tak is smaller but it demands a considerable mount.
If you want to draw a lineup make new friends at a star party .. the Tak will supply all weekend.
Noisejammer (Toronto, Canada), from an online thread entitled: Visual Only: 150mm Triplet APO vs 14″ Dobsonian.
Not unusual to get 1-2″ seeing here. I also observe from Mt Laguna ~7000ft elevation (which is about 50 minutes away) where on occasions I have experienced sub arc second seeing and Mag 6.8 skies. There with seeing better than 1″ my C8 shows an incredibly detailed Dumbbell nebula comparable with texture and detail reminiscent of my H-alpha shots of the nebula.
Even in average seeing from my backyard the 14″ significantly outperformed a very good 6″ APO I had. I sold that APO as it was simply too cumbersome to move and mount.
My personal experience suggests that there is simply no substitute for aperture in this hobby. But the reasons to acquire most scopes are driven more by personal preferences and not just objective performance criteria (which explains why I spend inordinate sums of money on premium refractors).
Astrojedi (Southern California, USA); from an online thread entitled: Visual Only: 150mm Triplet APO vs 14″ Dobsonian.
No 6″ APO can come close to what my 11″ to 18″ Zambuto and OMI Newts have done on the planets.
CHASLX200 (Tampa, Florida, USA), from an online thread entitled: Visual Only: 150mm Triplet APO vs 14″ Dobsonian.
A few years back I compared my TEC 160ED to my 14″ XXg Dob/Newt, my experience was that ‘planetary included’ (I think Saturn was mostly used), as the seeing improved, the 14″ started easily / obviously pulling ahead. Is not often we get seeing good enough for that, but the difference was obvious to my eyes, and you can see which one was sold.
Counterweight (Portland,Oregon, USA) from an online thread entitled: Visual Only: 150mm Triplet vs 14″ Dobsonian.
Is anyone, including the OP, truly cross-shopping these two scopes? While there are some opportunities for overlap, I will take my Obsession 15” every night, with the caveat that it takes time for the mirror to acclimate and the set up and collimating requires additional time/effort. I’m content with my 8” reflector most nights. I do like my refractor better on doubles, but the 15” and 8” will split tighter ones. Incidentally, my seeing is not great, but I have excellent transparency and minimal cloud cover most nights and my focus is typically on DSOs and there is NO CONTEST.
Rare indeed is the night when using my 15” that I say, gee, I wish I would have brought out the 120mm—or even the 8”, which has a fantastic mirror, and curved vanes. Possibly, only when the session had to be curtailed early because clouds rolled in. With the 120mm I’m frequently saying to myself, boy, that would be better with my reflectors. The exception might be on nights when I want wide views or merely to surf the MW.
Get a used quality big reflector and a less expensive, but still quite capable doublet refractor and never look back.
Chesterguy (Stllwater, Oklahhoma, USA), from an online thread entitled: Visual Only: 150mm Triplet vs 14″ Dobsonian.
Hi everyone. As the thread starter I wanted to let everyone know I’ve decided to go with a big dob. I am considering the Obsession Ultra Compact 22″ with go-to, which is roughly the same cost as a TOA150 mounted on an EM400.
jag32, from an online thread entitled: Visual Only: 150mm Triplet vs 14″ Dobsonian.
No we should all be using 60 mm stopped down to 40 mm. That would show that nasty ol’ bad seeing.
I agree with you about aperture. I’ve been using EDs and apos paired with each other (such as 81 mm on 130 mm) and on larger instruments (81 and 102 on c8 and c14) and have yet to come away thinking: “Thank God I have this here four inch refractor to save the night’s planet viewing.” The aperture always wins. On SCTs I amend the concept, I think the common wisdom that one subtract the diameter of the CO to get the equivalent apo diameter is a good rule of thumb. But even so the bigger scope can deliver more color saturation and more deep sky.
gnowellsct, from an online thread entitled: Visual Only: 150mm Triplet vs 14″ Dobsonian.
I happen to own a Orion Spaceprobe 3 and have owned at least one 70mm F/10 achromat.
A 76mm x 700mm spherical mirror is 1/12 wave. There is no need for a parabola, a spherical mirror is a nearly perfect parabola. The refractor has 4 surfaces that must be precise spheres and unlike the reflector, the surfaces not only need precise spheres, they also need precise radii to work together.
I would normally prefer a refractor over a similar sized reflector but in this case, this 76mm reflector has some real advantages both optically and mechanically. One advantage to the Newtonian is that the eyepiece is at the upper end of the telescope, this means the tripod can be lower and more stable.
Jon Isaac (San Diego, California, USA), from an online thread entitled: 76mm reflector versus 70mm refractor.
I think a 6” f/6 Newtonian with a premium mirror on a solid alt az with under 30% of CO could be one of the best “have the cake and eat it as well” secrets in amateur astronomy. Low cost, sharp views on planets that easily exceed those of a 4” apo (I also use a 4” fluorite Tak sometimes), bigger focus sweet spot and the advantage of almost fully illuminating wide field eyepieces to provide nearly 3 degrees of field.
Ratnamaravind (San Diego, California USA), from an online thread entitled: 6″ f/6 Newt OTA for $169.15
My mass-produce 16″ GSO mirror is tested at 1/14th wave p-v, and it beats the heck out of my 11″ Zambuto.
The point is, a 12″ GSO mirror that is barely diffraction limited will still show a tremendous amount more, with more detail, than a 6″ Zambuto.
From what I’ve been reading, GSO mirrors are not all going to be like mine by a longshot, but most of them do a pretty decent job; with just an ok mirror, I’ll take that 12″.
Codbear (Navota, California, USA), from an onnline thread entitled: Zambuto/Royce vs Synta/GSO.
If you are going to quote me, quote everything I wrote that is relevant: I did say this:
“Getting the performance possible from a larger aperture is more difficult because of thermal issues and as aperture increases, seeing becomes more and more of an issue. “
The question I was asked was to explain to [you] about why the wave front error is scaled relative to the aperture, why larger scopes have greater resolution. That’s pure optics, there are times when the seeing will support the larger optic.
If the best you ever see is 2″ and all you observe is the planets and double stars, first, you have my sympathy.. And in that case, the 6 inch might be a good fit but as I recall, Vlad’s simulation said a larger scope was still advantageous. The actual diameter of the first minimum of the Airy disk of a 12 inch scope is twice the Rayleigh Criterion, that’s about 2.2 arc-seconds. And as experienced planetary observers like Alan French will tell you, even in poor seeing, there are moments of stable seeing where the large aperture can be used advantageously.
In my world, 2″ is rather poor seeing for viewing the planets, being south of the jet streams close to the Pacific ocean in one of the worlds mildest climates has it’s advantages. The greater resolution and contrast possible with a 10 inch, 12 inch, 16 inch scope can be used to a good advantage.
Last night I spent some time on the star Jabbah, with my 10 inch. It’s a pair of doubles, one is 1.3″, the other 2.2″ , both were wide clean splits, the seeing was well under 1″. The views of Jupiter and Saturn were quite nice in my 10 inch.. Viewing the planets, I generally stop at 410x, the 0.6mm exit pupil is quite dim. That’s where I stopped last night.
I did start the scope cooling with the fan running about an hour and a half before sunset. The scope just has generic Taiwanese optics, decent optics, I’ve split doubles slightly under 0.5″, that won’t be happening in a 6 inch.
John Isaac(San Diego, California, USA), from an online thread: Zambuto/Royce vs Synta/GSO.
An instructive reminder (and very sobering for refractor nuts) of the effects of an obstruction in Newtonian(and other) telescope optics by engineer and veteran astro-imager, Thierry Legault. See here for details.
Looks like you have some pretty nice gear already. Sell the DM4 and get an 8″ dob for observing.
Keith Rivich, (Cypress, Texas, USA), from an online thread entitled: 4″ ED refractor vs 6″ f/5 for visual on a DM4?
Both are really fine choices for grab and go and visual. I have both, and Both produce an image that is more alike than different.The refractor will be easier on cheap wide field eyepieces.The newt will give you more light to work with. I would lean toward the newt given the big price difference that you see.
vtornado, (Northern Illinois, USA), from an online thread entitled, 4″ ED refractor vs 6″ f/5 for visual on a DM4?
6″ F/5 wins in all areas (even FOV vs 900mm ED)
Nicolelouda, from an online thread entitled: 4″ ED refractor vs 6″ f/5 for visual on a DM4?
The price differential between a newt and a 4” refractor is quite large where I am, so this is in newt’s favour. I do like the ease of use of a 4” refractor. What do you think?
Curious; I find a 6-inch f/5 Newt much easier to use than a 100-mm refractor, except for the cooldown period.
In all likelihood, the views of planets and other bright objects would be much the same between the two instruments, but if the Newt has a really good mirror, then it would be clearly superior. Not by a huge margin, however.
The main virtue of the 100-mm APO for me would be the significantly wider well-corrected field of view. Depending on the APO’s focal ratio, of course.
Tony Flanders (Cambridge, MA, USA), from an online thread entitled:4″ ED refractor vs 6″ f/5 for visual on a DM4?
I have owned a couple of 6 inch F/5’s and a couple of 4 inch ed/apo refractors. 6 inch F/5 Newtonians tend to get into SCT size central obstructions and thermal equilibrium is not a given the way it is with a refractor. I would go with the refractor because it’s more reliable, it’s provides nice views of the planets without waiting for it to cool.
Jon Isaac (San Diego, California, USA); from an online thread entitled; 4″ ED refractor vs 6″ f/5 for visual on a DM4?
The “Cheap Dobs” from the 5 and dime have gotten to be quite excellent, at least in sizes 12″ and under and I’ve seen them personally give the “premium” dobs a run for their money!!
Barbie, from an online thread entitled: Zambuto/Royce vs Synta/GSO.
6″ f/5 newt. To my eye though the 4″ ed will be sharp and high contrast, 6″ will out resolve it.
Izar187(43 degrees North), from an online thread entitled; 4″ ED refractor vs 6″ f/5 for visual on a DM4?
For what it’s worth –
A good friend owns a “premium Dob” company – and will put whatever optics you want in your telescope. His personal rather large Dob has a primary by one of the commonly noted premium mirror makers (not Z or R). He has seen them all and can have whatever he wants – and picked what he wanted. I’ve observed with this scope – and it performs!
He also sells Dobs with GSO mirrors – if that is what the customer wants. He has said that the recent GSO primaries he as gotten have been quite good. From my experience – this guy knows what he is talking about – and can tell a great mirror from a fair one.
While I suppose you can get a less-than-wonderful mirror from GSO – there seems every reason to expect many current ones will be very fine. If it is ‘junk’ – return it – or have it re-figured.
George N (Binghamton & Indian Lake, New York, USA), from an online thread entitled; Zambuto/Royce vs Synta/GSO.
I was observing Jupiter and Saturn at 250x with my 6″ F8 ‘Mass produced” optics Saturday night and they didn’t even break a sweat!! I could have gone higher but didn’t have the eyepiece/barlow combination available to do so. I’ve also had high end “hand figured” optics and mass produced optics at the same time and compared them side by side and found(after 50 years of observing and testing) that there is little to no difference between TODAY’s mass produced optics and the more expensive “hand figured” optics, other than cost and bragging rights!! Hand figured, mass produced, if it shows me what I want to see, then I’ll buy it!!
Barbie, from an online thread entitled: Zambuto/Royce vs Synta/GSO.
ALL of these mirrors have their place, it’s not a matter of one OR the other, just like there’s more than one brand and model of car. The GSO / Synta are great for their low cost. At some point of involvement in the hobby some people want better and the market is there to answer, whether it’s a premium mirror or a Feathertouch focuser. The mass market mirrors are getting better and better, and that’s a good thing, but my experience and the experience of many others is that they’re still not equal to one made by a master craftsman and probably will never be. The difference between them is getting smaller, but it’s real. The bottom line is use and enjoy whatever you have and don’t worry about what others choose to do.
bvillebob(Oregon, USA), from an online thread entitled, Zambuto/Royce vs Synta/GSO.
The right answer will depend on individual preferences. For me the answer is very simple… 10”. No 6” scope, even a premium refractor will show more than a 10”. A 10” of even average quality optics will do everything better. Period.
Astrojedi (Southern California, USA), form an online thread entitled, Zambuto/Royce vs Synta/GSO.
Premium mirrors are a marketing device, people buy them for bragging rights or piece of mind, or feel they deserve such luxuries,but the views they produce are only marginally better on some objects , about the same on most objects. Other variables ,especially seeing conditions, collimation,tube currents, eyepieces, stray light, local thermal issues, secondary, exc, etc, are far more important then the alleged smoothness of the premium ,gourmet mirror.Folks that purchase such stuff, probably also buy paracors,premium hand grenade eyepieces,top shelf collimation aides,fans, etc, they usually although not necessarily are better at controlling the variables I mentioned and thus get the more from their scopes then the average mass market guy, and hence better views that they will attribute to their magic mirrors.
tommy10 (Illinois, USA), from an online thread entitled Zambuto/Royce vs Synta/GSO.
After owning 12.5 and 15 inch scopes, I appreciate my 8” dobs much more. Now that I know what to look for, I’m seeing things that I didn’t know I could when I started out with my first Orion 8” dob. The amount of detail visible in galaxies is the most surprising. As has been said here many times before, all large scopes do is magnify galaxies, they don’t increase their intrinsic brightness. So now I try to see the galaxies as simply smaller versions of what I saw in my bigger scopes, and I’m seeing things I never thought I could. I just had to change my expectations, and observing techniques. I’m getting to the point where I don’t want an F5 scope of any size, because of my aging eyes and their short depth of focus. So for me, going smaller and slower with an 8” F6, or even a 6” F8, is not only doable, but probable, maybe in the near future. When I want to do some serious observing, I break out the 8” F9. I haven’t even scratched the surface of what this scope can do.
Galicapernistein, from an online thread entitled; Versatility of a 6″ Newt
6″ is enough to get interesting views. M13 starts to break up. Planets start to get beef that the 4″ can’t muster. The view is wider. And the scope is portable.
But 6″ is mainly a grab n go. If you drive way out some place dark, you will want a 10″ to enjoy the night. Even at home, the 10″ will be much better on planets.
Stargazer193857, (Southern Idaho, USA), from an online thread entitled: Versatility of a 6″ Newt
Long ago I had a 6″ F8 with 1/8 wave optics and it gave views comparable to my WO ZS110 refractor for planets but brighter on DSOs and not far behind my IM715D mak with a much wider FOV.
dscarpa (San Diego, California, USA), from an online thread entitled; Versatility of a 6″ Newt
There seem to be generalizations flying both ways and neither are fully accurate.
The premium mirror makers are not fly-by-night operators. They are folks who have established solid reputations over the years by producing quality optics. And for many observers these mirrors are very much worth it even with a little wait time. To me for example an excellent/premium optical figure is immediately obvious but I am still very satisfied observing with other scopes. Many here are not.
On the other hand Commercial mirrors receive more Q&A than folks here are lead to believe. Manufacturing technology and overall processes have come a long way in the past decade have improved in leaps and bounds. These days based on the sample set of very recent 20-25 Celestron and Sky-Watcher as well as GSOs that I have looked through the mirrors have been very good – almost 95%+ are diffraction limited. Most harmful issues actually arise from other factors in the scope – alignment, cooling, collimation, baffling etc. This is why differentiation for the premium mirror makers is now shifting to larger mirrors and/or faster focal ratios where the commercial operations are yet to catch up (and they may never go there).
To me the Op’s question is a matter of personal preference as much as it is of performance.
Astrojedi (Southern California, USA), from an online thread entitled; Zambuto/Royce vs Synta/GSO.
I have been involved with manufacturing (including toys) in prc for over 2 decades, I concur with Jon’s experience. My extended family in prc are challenged daily in finding quality products and truthful information. But with wages stagnating stateside, i understand why I too have fallen for the China price.I plan to take my orion xt10g to the grave.
waso29 (USA), from an online thread entitled: Zambuto/Royce vs Synta/GSO.
We are definitely spoiled in this age of being able to get telescopes shipped to our doors that once upon a time were restricted to the realm of a dedicated observatory, and affordable by the masses. I’m thankful for all of it, which is a large part of why I said yes to this little guy. I don’t know how regularly it will collect photons, but it can definitely serve a good purpose.
BlueTrane2028 (Bala Cynwyd, PA, USA), from an online thread entitled; “Junk” Orion Spaceprobe 3″
I’ll take a pic eventually, but a 3″ mini-dob has been made.
Used an 18″ length of 1″ black iron pipe, two floor flanges and a street elbow. Made a box to fit around the OTA to hold it and to bolt to one of the flanges, bolted the whole affair to a circle of wood I bought at Lowe’s.
Black pipe is way too much money, so I’m in it a few bucks more than I had hoped to be… but the little scope has already proved itself to be decent. The mount needs a little work yet but it’s not shaky which is obviously good. Optically, it may be that my eyes are good, or it may be that I know it’s there… but I swear I could see the Cassini division (barely) and some surface banding on Saturn with a 6mm Expanse eyepiece in this thing. It’s clearly not a deep sky scope, but it’s plenty fine as a quick grab.
I’m not sure what role it will play in my collection (since I have other quick grabs), but it’s now completely usable.
BlueTrane2028 ( Bala Cynwyd, PA, USA), from an online thread entitled; “Junk” Orion Spaceprobe 3″
My old 10″ f/4.7 Dob with Synta optics was there as well, now owned by a club mate. It definitely put up sharper high magnification images of Mars than the ED150 last night.
J.R Barnett (Petaluma, California, USA); from an online thread entitled: Update on my SW ED150 order.
I was just observing Mars,Jupiter and Saturn at 250x(I could have gone even higher but didn’t have the eyepieces/barlow combination available to do so) this evening with my Orion 6″F8 dobsonian and had some incredibly sharp and detailed views of these planets so I would say the Chinese optics are more than up to the task for serious astronomical observations where critical fine details are to be seen. The clear sky chart for my area was indicating average seeing and transparency but I easily saw the Crepe ring of Saturn with Cassini’s division sharply defined as well as multiple bands on the globe. Mars also looked good, although still not prime due the remaining dust but Syrtis Major was seen as well as the SPC. Jupiter featured numerous bands with festoons and the GRS. Also viewed Epsilon Bootis(cleanly split), Mizar/Alcor, Alberio and M29 all from heavily light polluted and haze filled skies. Not bad for an hour long session before bedtime!!
Barbie; from an online thread entitled, Zambuto/Royce vs Synta/GSO.
Yes, there is for me. Deep-sky observing really starts to come to life with a 10. And in good seeing, it outperforms the 5-6″ class ED fracs on planets. I think the 10″ dob occupies a unique niche among telescopes. Anything bigger becomes cumbersome to handle solo. Anything smaller leaves me wishing for something bigger too often.
If I had to live with just one scope, it would be a good 10″ dob.
Precaud (north central New Mexico, USA), from a thread entitled; Difference between 8 inch and 10 inch Dobsonians.
You have ruled out a 12 inch Dob. Maybe you could reconsider. A 12 inch gathers more than twice the light over an 8. You will notice quite a difference in all objects with a 12–if the optics are of good quality. I own a 12.5 inch Portaball, and it performs outstandingly on planets, globulars, open clusters, double stars, and fairly well on nebula and galaxies. Why would you rule out a truss tube? You could move up to a 12 truss from an 8, with ease of hauling, set up, take down, and storage. I store my 12 inch Portaball inside of my house on my side of the closet.
Gene T ( south Texas, USA); from an online thread entitled; Difference between 8 inch and 10 inch Dobsonians.
I like what Karl pointed out in the previous post. There is more than the aperture gain to consider. You make no mention of how far you plan to carry this scope or how often you plan to load or unload it. All factors to consider. I had a 10″ that was admittedly an older sonotube variety and it was HEAVY and had to be split into two parts in order for me to carry it any distance. I was younger and certainly fitter at the time. I currently have an 8″ that I can carry as a complete unit and can carry it for some distance without strain because of the lighter tube, mirror and base. I might be able to do the same with a 10″ from the same manufacturer, but it would be pushing it and I’m not getting any younger.
The point, which is often made here, is that there are always compromises. I find myself using the 8″ much more than my 15″ partly because of the ease of set up, even though the 15″ doesn’t take that long. Obviously if the night looks like it will really be great, I have plenty of time or I can travel to a dark site than it’s worth it for the greater light grasp and additional effort of the larger aperture otherwise one can find and enjoy quite a bit with 8″.
Chesterguy, (Stillwater, Oklahoma, USA); from an online thread entitled;Difference between 8 inch and 10 inch Dobsonians.
Same here I only own an 8 inch currently and will one day jump to a 12 inch solid tube! I think for my personal preference I would not want to setup a truss every time I had to observe. Nor would I want to spend the extra money on the truss style setup and then be forced to buy a shroud on top of that. I’m a true rookie but from what I have read a truss design up to even a 12 inch doesn’t seem to be a benefit once you consider the extra steps of setup. In top of that they don’t seem to drop weight at all compared to solid tubes as far as I have read on the specs pages of any of the scopes I’ve looked at. They will definitely be easier to store but at the cost of not wanting to deal with setup? Not worth it. Buy solid tube avoid dew issues and body heat running through the shroud. That’s what I have learned from the forums I’ve read. Obviously far more experienced people out there than me but I’ve read a lot of what experienced people have to say.
Ken 83 (Connecticut, USA), from an online thread entitled; Difference between 8 inch and 10 inch Dobsonians.
I’ve got an 8 solid tube and a 12.5 truss. Guess which one I use twice per year at Cherry Springs and which I use often. From 8 to 12.5 is about one magnitude, so 8 to 10, I’m thinking is about half a magnitude.
Deep 13, from an online thread entitled: Difference between 8 inch and 10 inch Dobsonians.
…..the move to 10″ won’t give some improvement in viewing, but it is a half step at best, and may not prove to be as satisfying as some post suggest. Sadly, this is one of those things that people usually have to see for themselves to judge if it was worth doing. From 8″ to 12″ though is a much more obvious and dramatic step that anyone will see.
Eddgie, from an online thread entitled: Difference between 8 inch and 10 inch Dobsonians.
I will take the OP at his word that he’s done his homework and is satisfied a 10″ scope is all the upgrade he wants to consider. My C11 was a significant and noticeable improvement in viewing over some friends’ C8s. Familiar objects were brighter and more enjoyable to look at, AND objects that were too faint to be interesting to me opened up and became targets I sought out. Very worthwhile for me. Skip forward a few years to a shoot-out between my C11 and a 10″ scope. The 10″ scope won for cool-factor and my perception that the image wasn’t degraded by the loss of 1″ aperture. I sold, with a heavy heart, my C11 and kept the 10″.
That’s a long, round-about way of saying that for me, a 10″ scope is a worthwhile upgrade over an 8″ scope for deep sky.
To confuse things, I am perfectly happy with my 8″ driveway scope for lunar, planetary and double stars. I never used my 10″ or 11″ scopes at home because they needed my G11 which was a pain to assemble and set-up for an hour’s viewing (I know, not a problem for our Dobsonian-owning OP). My 8″ driveway scope requires only an Orion Sirius which I leave assembled and carry out of my garage in one trip, gives satisfying resolution (560x was not empty magnification on two near-perfect nights, 240x regularly), and provides images bright enough to trigger even my lazy color receptors so Jupiter and Saturn are more than just yellow and brown. So, there’s my case for the 8″ scope, if you’re a lunar/ planetary observer.
macdonjh, from an online thread entitled; Difference between 8 inch and 10 inch Dobsonians.
Jupiter in my 10 inch Dob
Main reason (which I think but could be wrong): Good seeing with steady high altitude air. Planet high in the sky (winter).
InkDark(Quebec, Canada), from an online thread entitled; Your best view through a reflector.
For planets it would be through the 18″ f/5.5 dob I built in the early 90s. Looked at Jupiter on a night of excellent seeing using a 4.8 Nagler and 2x barlow giving 1058X. Felt like I was in orbit around the planet. The details rivaled Voyager images. Never saw it that good again.
Second was using a 14″ f/7 homebuilt dob 250 miles NW of Sydney Australia. I was touring the Small Magellanic Cloud and got stuck on the Tarantula Nebula. It was bigger and brighter than the Orion Nebula and it wasn’t even in our galaxy!! I used an OIII filter, UHC filter and no filter. It gave a very different look each way and was spectacular each way.
Don W(Wisconsin, USA), from an online thread entitled; Your best view through a reflector.
Best view of a planet: Jupiter at 456X due to superb seeing conditions So many details a drawing would be impossible plus albedo shadings on Ganymede
Saturn at 1123x due to superb seeing, in which “spokes” shadings were seen on the rings, and the C ring went down almost to the disc of the planet.
Uranus at 493x due to excellent seeing, in which a transitory white stripe was seen by a few of us.
Best view of a galaxy: M51, wherein the dark lane in the bridge was visible, the “D” shaped bright area around the companion and 3 fingers of faint extension and a feathered spiral stucture extending from the main galaxy on the side opposite the companion. Spiral pattern and clumps in the spiral arms all visible. Superb transparency, a very dark night, and good seeing conditions all together.
Best view of a globular cluster: M15 fully resolved to the center into tiny little pinpoints all the way across the field and even as it exited the field. Superb seeing conditions and excellent eyepiece.
NGC104 in which the predominant color of the cluster was yellow due to the high density of red giants. Superb seeing and larger aperture (18″)
Best view of a planetary nebula: NGC7009 (Saturn Nebula) with center oval details, outer glow and satellite “pods” visible at 493X. Excellent seeing and transparency.
Best view of faint stars: O/A/B giant stars in NGC206 in M31–superb seeing and darkness
Best view of a star cluster: NGC7789 on a night of superb seeing and transparency
Best view of a nebula: M20 on a night of great darkness and transparency: the blue area completely surrounded the emission part and the center stars in the emission art formed a long “L”. Superb seeing, transparency, and darkness
M17>M16 where nebulosity was tracked from one nebula to the other–excellent transparency and darkness
M17 with the nebula completely filling a 42′ field and the “swan” only a portion of the visible nebula.–superb transparency, seeing, and darkness.
NGC6888 where the large oval was filled from one end to the other with ropy tendrils and a tendril in the center made the nebula outline look like a Greek theta. Fantastic darkness and transparency.
The Veil nebula wherein the Witches broom handle looked like a tubular-shaped filligree of silver–superb seeing and transparency.
NGC2359 in which 4 extensions from the center bubble could be seen and thin striae of nebula covering the center bubble. Fantastic transparency.
M27 in which ropy “berms” of nebulosity could be seen surrounding the long oval part of the nebula–excellent transparency and seeing, allowing for a high power view.
M76, where the outer ansae joined to make it look like a 2-handled beer stein. Amazing transparency and very high power due to good seeing.
Eta Carinae in which the homunculus in the center appeared gold in color against a rose colored outer nebula (dark skies and 18″ aperture)
I could go on and on. Too many things to list.
Factors of importance: Transparency, Seeing, Darkness, collimation of the optics, cooling of the optics. When they’re all good—-MAGIC!
All views were in the 12.5″ except where noted.
(Starman 1) Don Pensack (Los Angeles, California, USA); from an online thread entitled: Your best view through a reflector.
Best planetary- Jupiter/Saturn same night in my 8″ Orion due to good seeing and slow speed of the scope
Best DSO – Orion Nebula in my 12″ Lightbridge (with custom mirror). Could see green, blue, and alot of structure detail.
Blakheaven( NE Oklahoma, USA), from an online thread entitled: Your best view through a reflector.
Jupiter and Saturn in my 6″ F8 dobsonian. Saw albedo features on Ganymede and 4 moons around Saturn along with Encke’s minima and the crepe ring and many swirls and festoons in Jupiter’s belts and with detail around the GRS. I was using 298X and could easily make out all of these features in the best seeing I’ve experienced in my locale in many years!! Along with the seeing, I also attribute the fine optics of my Orion Skyquest XT6, of which I have gotten an excellent sample!!
Best DSO: Orion Nebula complex during the winter of 2017 in my 40+ year old Japanese Erfle eyepiece in the aforementioned 6″F8 dob.
NOTE: My optics were perfectly aligned and properly cooled which I believe to be two of the most important factors in seeing these details.
Barbie, from an online thread entitled; Your best view through a reflector.
Jupiter in John Prattes 32” at the Winter Star Party a couple of years back. Everything I hear about the steady Florida sky was true that night. At 909x, the image scale was huge and the planet rock steady against the sky. It was literally impossible to describe what I saw, an image only rivalled by spacecraft flyby. Transparency and darkness were irrelevant, it was the steady sky and large, superb Lockwood mirror that made that view possible. A view I will never ever forget.
Every time I view an object with my 32” the first time, is basically a lifetime best view. Galaxies and Planetary Nebula in particular look incredible in the big dob. On a great night of seeing, at high power, the Homunculus at the heart of the Eta Carina Nebula looked like a Hubble image. That’s probably my favourite so far.
I get to observe where the sky is as dark as it can get, and the transparency is generally at the top end of the scale. But the memorable sessions usually occur when the seeing conditions are very good, which is hit and miss at my dark site. I would be happy to trade a little sky darkness for regular steady seeing. That combination and large and high quality optics make for the best combination.
Allan Wade (Newcastle, Australia); from an online thread entitled; Your best view through a reflector.
Saturn – 8″ Discovery dob w/ plate glass mirror was left outside all night with the top capped. I woke up before dawn, then used my 4mm Radian for a 300x view.
It was one of those very calm summer mornings where transparency wasn’t the greatest, but the air was rock-steady.
I could have watched it for much longer, but the sun soon came up.
Bill Schneider(Athens, Ohio, USA); from an online thread entitled; Your best view through a reflector.
Mars in the 20″ f/5 [Obsession] in 2003. The seeing was excellent and the detail was fantastic, with both moons visible at the same time as a bonus. Once the aperture is well into the large range, there is no substitute for superb seeing.
For DSO’s there have been so many moments that I could not pick a single target or even a single instance of a particular target. I got started on the path to the 20″ after viewing M51 through a 24″ Tectron in dark skies 20+ years ago. As good as the view was through the 24″, the eventual views through the 20″ have been sharper.
Redbetter, (Central Valley, California, USA); from an online thread entitled; Your best view through a reflector.
The best view ever was through someone else’s 18 inch(?) Dob of Jupiter at a star party, high up in the alps in Europe. It was one of the darkest skies available in the country where I was living, the telescope was expertly handled, and the mirrors well cooled I would imagine.
X3782, from an online thread entitled, Your best view through a reflector.
An 8 inch is a very capable scope and a can be lifetime scope for a serious observer.
Jon Isaac, (San Diego, California, USA); from an online thread entitled; Difference between 8 inch and 10 inch Dobsonians.
I have observed for ten years with an 8″ f6 dob. I do own a 12″, but the 8″ is my main scope and love it. I never stop learning about the sky with it. Maybe mine is so good because I didn´t buy it for Christmas?
But you are right, when I show the moon, Saturn, Omega Centauri or even a bright PN to a neighbor that has never observed through a telescope, they always say: “This is very nice, but if you only had 2″ more…”
Javier1978( Buenos Aires, Argentina), from an online thread entitled, Difference between 8 inch and 10 inch Dobsonians.
Can’t do just one.
Jupiter at 1100X (stacked Barlows) in the 18″ I owned at the time, late 1990s, very dark sky, excellent transparency and seeing. Jupiter full of detail, whorls, storms, bright color bands. At Blue Canyon.
M51 a blazing blue, at the zenith, excellent transparency and seeing, 18″, late 1990s, Blue Canyon.
Double quasar in Ursa Major, high in the sky, with my 22″. From an average sky, suddenly thee were so many stars it was hard to make out the constellations. It was February, the Double Quasar was high, found N3079 and immediately thereafter, at about 600X, the components were visible, seemingly pulsating at different rates. Great sky lasted for 20 -25 minutes. Lake Sonoma.
Eta Carinae, at Magellan Observatory in Australia, 24″. Most unique visual object for amateur telescopes.
Results of the spacecraft that crashed into a comet, I and two other observers saw “sparklies” for about 8 minutes after it hit (time adjusted for lightspeed). 18″.
Shneor(Northern California, USA), from an online thread entitled; Your best view through a reflector
Double cluster in 12” dob with 17T4 is one of my all time favorites.
Kadmus, from an online thread entitled; Your best view through a reflector
Have you ever thought about a larger Newtonian? I have seen some fabulous high magnification planet images in 14 and 16 inch Zambuto mirrored Dobsonians that track. A quality mirror and good collimation will provide dynamite planet views.
ShaulaB(Missouri, USA), Best scope for planetary-star cluster observing.
In my experience the best planetary scope is a premium 32″ f3.3 Dob located in the -34o latitudes of the southern hemisphere in a very dark outback location. Same as observing everything else – aperture, optics, location and careful attention to details pays off big. It is likely a similarly located, configured, and well executed Dob of larger aperture would be better.
Star clusters? Same thing. Individual stars, nebulae, galaxies, etc? Same thing.
It’s difficult to answer the “What’s BEST?” question when it’s unqualified.
Your 16″ Dob should provide extremely satisfying planetary and other observing if collimated and cooled in a dark location when conditions supported good observing. Mine sure does. I’ve had owners of large and very fine Stellarvue APO refractors take a look at Jupiter and immediately decide they need a medium-large Dob for planetary.
Havasman (Dallas, Texas, USA); from an online thread entitled: Best scope for planetary-star cluster observing.
You can actually make a case that a really large (maybe 6″?), premium apochromatic refractor with a great eyepiece might beat what that 16″ Dobsonian will do for you. Even if the view is not necessarily better you just might find the experience more pleasurable.
But the price would be shocking for most of us and you might find that you actually like what the 16″ Dob does either as well or better. A 6″ refractor also generally starts getting rather long and that often means less-than optimal ergonomics on some targets.
If I had a 16″ Dobsonian and was thinking about getting better views I’d probably consider retro-fitting a GoTo system to the Dobsonian rather buying a big refractor or Mak-Cass. The tracking reduces the distraction of having to nudge the Dobsonian along and that means you will actually see a bit better.
If your intent were to do planetary AP then I’d be looking for something like a 14″ SCT and Barlow the thing. It’s actually a great instrument for visually observing planets as well and might compete fairly well with your 16″ Dobsonian in part due to the long “natural” focal length and the relatively good ergonomics for most targets. But especially if you got a 14″ SCT with a fork mount – not fun to try to move around/set up.
Olecuss, from an online thread entitled: Best scope for planetary/star cluster observing.
Why doesn’t your 16″ work for planetary/globulars?
If it’s cooled down properly, collimated, and has a good mirror, it should perform far better than literally anything else besides a bigger Dob.
Augustus (Connecticut, USA), from an online thread entitled: Best scope for planetary/star cluster observing.
I’ll second the pairing of a large Dob with a fast 100mm+ refractor. I keep mine on separate mounts.
epee, from an online thread entitled; Best scope for planetary/star cluster observing.
Assuming that his 6-inch f/6 has a first-class mirror and is well-collimated and cooled, it’s going to equal or beat any affordable refractor on the planets and on the overwhelming majority of clusters. But a good 4-inch APO would come close on those, and beat the Newt on wide-field viewing and thermal characteristics.
Tony Flanders (Cambridge, MA, USA); from an online thread entitled; Best scope for planetary/star cluster observing.
And while I agree that the 120mm ED is a beautiful scope, mine lasted about 4 months before I got bored with it. I would look at even bright targets with the 120mm but if those targets would fit into the field of my 12″ Dob the were always much more pleasing to me in the bigger scope.
Eddgie; from an online thread entitled; Best scope for planetary/star cluster observing.
[Snip] “You can actually make a case that a really large (maybe 6″?), premium apochromatic refractor with a great eyepiece might beat what that 16″ Dobsonian will do for you. Even if the view is not necessarily better you just might find the experience more pleasurable.” End Quote.
In my opinion, nope.
I have access to 6″ and 11″ refractors of very good quality and they do not come close to equaling or surpassing my 18″ Obsession.
Keith Rivich(Cypress, Texas, USA); from an online thread entitled: Best scope for planetary/star cluster observing.
To each his/her own. I spend a week to two weeks a month observing under reasonably dark skies. There’s a lot to see in a 16 inch or 22 inch scope that’s simply beyond the reach of a 6 inch. The number of objects visible is dramatically increased as it the detail visible in existing objects .
This is not to say , there’s not room for a smaller scope but a 6 inch F/8 apo/ed would not be my choice. My 12.5 inch F/4.06 operates at a 1482 mm focal length with a Paracorr so the maximum field of view is only about 19% narrower but it shows much more and is an easy scope.
When I go small, I want something in return, a wide field of view with a bright image to see those objects between binos and a 10 inch F/5 or a 12.5 inch F/4.
Sure a 12.5 inch or 25 inch doesn’t show everything one might see in the photos but there is still plenty to see. It takes me about 10 minutes to setup the 16 inch when we’re camping in the motor home and it might be a week or so until it’s time to tear it down, not much trouble at all.
Jon Isaac(San Diego, California, USA), from an online thread entitled; Best scope for planetary/star cluster observing.
My refractor story is too long for a post. Over the years I have owned a number of refractors of various apertures focal lengths and types. I like refractors but I also like reflectors and appreciate the capabilities and limitations of each.
I like ed/apo refractors because they are the most efficient scopes in terms of performance per inch of aperture. They offer wide field views and within the limits of their aperture, they offer the most performance at high magnifications. For astronomy, they’re the ultimate grab and go telescope. The image is erect so they’re well suited for terrestrial viewing.
But ultimately, the resolution and fine scale contrast as well as the light gathering power of a telescope is related to its aperture and so for high resolution, high contrast observing like the planets and double stars as well as going deep, I use reflectors, these days Dobsonians.
Jon Isaac (San Diego, California, USA), from an online thread entitled: What’s your refractor story.
When I considered all the different factors, especially cost, a high quality, long-focus, optimized Newtonian always came well ahead of any other option. A large, apochromatic refractor would probably be the most desirable option if money wasn’t a factor but might be ten or twenty times more expensive than a Newtonian of the same aperture optimized for planetary observing. In the course of more than 50 years as an amateur astronomer and >30-years making telescopes, I have never looked through a better planetary telescope. (with one possible exception). On nights of steady skies, it is capable of giving exceptionally sharp, high contrast images.
David Lukehurst (Telescope Maker, Nottingham, UK), discussing a 9.5 inch f/9.8 Newtonian reflector, from an online advert; source here.
A good 10″ mirror will best a top quality 6″ APO. A lot of APO folks may no[t] like it or may disagree, but I’ve seen it many times. Most reflectors are not really well collimated. Some not well at all, some just OK. They are more finicky of collimation and tend to be slapped together on site. No contest unless the seeing is really poor, or the 10 ” reflector is just bad or poorly collimated.
Bremms (South Carolina, USA), from an online thread entitled: Refractor or Reflector for most optical resolution.
I think db2005’s statement about obstructed optics does not apply to resolving power. As George stated, aperture diameter is the primary parameter determining resolution. An obstruction may reduce detail or contrast on an extended object like a planet or the moon, but it won’t impact actual resolution for the most part. Some people who are hard core double star observers actually prefer a central obstruction because it will actually increase resolution when looking for the separation between the two components of a close double. This is because the central obstruction actually puts more light in the 1st diffraction ring at the expense of light in the airy disk, so the airy disc looks smaller which helps resolving close doubles.
fcathell (Tucson, Arizona, USA), from an online thread entitled: Refractor or Reflector for most optical resolution.
One also needs to understand that refractors even APO have chromatic aberration that lowers resolution. The eye and brain are very good at focusing on the image in a refractor that is in focus while ignoring the out of focus image. A camera see[s] all so you have a sharp image swimming inside a blurry one. Ask any planetary imager about trying to take high resolution images of the planets with a refractor and they will tell you that you need to take Red, Green and Blue images thr[ough] filters were the focus is adjusted for each color and then combine them. If not the image is soft because the camera sees the out of focus wavelengths from the chromatic aberration of the lens. That is why modern DSLR CCD cameras have IR blocking filters built in since camera lens are not corrector for IR and if not block the CCD seeing this out of focus image.
Aperture determines resolution, the bigger the aperture the better the resolution. The issue is that when people start comparing refractors to reflectors they aren’t taking into account the actual quality of the optics of those two exact telescopes being judged. One needs to first look at what the theoretical resolution of any optical system could be and then actually bench test that system to see how well it was made. A poorly made reflector will easily be beaten by a well made refractor but that doesn’t mean one type is better then another.
DavidG (Hockessin, Germany), from an online thread entitled: Refractor or Reflector for most optical resolution.
Optical resolution depends on the aperture and nothing else. Assuming a quality made scope, the potential resolution will always be larger with a larger aperture scope. It’s a mathematical certainty. Seeing conditions will dictate whether or not the theoretical resolution is ever achieved (it may never be). You do not subtract the diameter of the secondary to determine the resolution………….a larger aperture will absolutely produce a higher resolution image if the focal length is matched appropriately and the seeing conditions allow.
Tom Glenn, (San Diego, California, USA), from an online thread entitled: Refractor or Reflector for most optical resolution.
I had a 6-inch F/12.5 Newtonian over 50 years ago that formed Spectacular planetary images. And was actually excellent on the other usual suspects. It’s hard to explain, but a slow system feels somehow more comfortable on the eyes that these fast ones can’t match. As if the eyes know the telescope isn’t fighting itself to form a good image. That might be just psychological, but I suspect there is something to it. Kingslake and Sinclair called it “ray-bending.” The less the optics have to bend the light, the easier is the design, fabrication, alignments and comfort of use.
Tomdey (Springwater, New York, USA); from an online thread entitled, Long Slow Newtonians.
I have owned around ten 8 f/8 Newts and all gave a great image.
CHASLX200 (Tampa, Florida, USA), from an online tthread entitled, Long Slow Newtonians.
I have a 6″ f/10 Newt with an Edmund Scientific premium, spherical primary mirror with a small (20mm) secondary mirror on a curved vane spider. When I do a direct comparison with my 6″ f/8 Criterion Dynascope … which is a nice scope in it’s own right … the 6″ f10 has better contrast for planetary observing and a darker sky background when observing deep-sky objects at similar magnifications
The differences are very noticeable and somewhat surprising since the f/10 is a spherical mirror. However, the differences and capabilities of long focal ratio spherical mirrors versus the more traditional medium focal ratio parabolic mirrors is a well worn topic on CN.
*skyguy*(Western New York, USA); from an online thread entitled; Long Slow Newtonians.
Three of them over the years: 10″ f/9, 8″ f/9, and 16″ f/7.
It’s nice when the entire FOV is the sweet spot.
It’s nice when any eyepiece that finds its way into the focuser gives a great view.
It’s nice for minimum glass planetary work.
It’s nice when collimation is easy (getting the optics mounted inside the tube is almost enough).
It’s nice when collimation holds all night. No excuses performance.
Not so nice of a tube size and mount. But, I still have a soft spot in my heart for them.
Jeff Morgan( Prescott, Arizona, USA); from an online thread entitled, Long Slow Newtonians.
Just finished the 6″ f/8 Edmund. Mirror came off eBay and it is fantastic like all Edmund mirrors. Stars are pinpoint sharp and sky background is pitch black. Hate to say it is so refractor like. People idolize lenses but quality mirrors are every bit as good.
Starlease (Rocky Mountains, USA); from an online thread entitled, Long Slow Newtonians.
I ve got a 6 inch f 8 mirror I bought in the late 90s…is probably an Edmund one as well (says ES and few other things on the back).
That thing REALLY performs. And this is only so so main mirror collimation, a slightly twitchy focuser made of plastic plumbing parts….the diagonal is just some run of the mill thing that I have no idea of the specs on but it was something cheap I also bought back then (or in other words not some fancy 1/30 wave thing). The spider is made of something like 1/8 RODS (or bigger!) rather than thin metal vanes. The secondary can’t even be adjusted. My high power eyepieces are a oooolllld University Optics 6.8 ortho and a 10 mm 3 element Vite $10 eyepiece (with a plastic lens!).
I’ve been watching the Mars observation reports here. I’m seeing more detail than most people are reporting here (even when a fair number of them are seeing nothing more than the polar cap). Some photographs with signifcantly large scopes are about the only thing besting my observations. Even during the height of the dust storm I was getting large scale stuff (low contrast to be sure but definitely there).
Been doing public star gazes. Random John Q publics can often even see the large scale details with the $10 Vite !
Imagine if I did this thing up right !
I would prefer it to be more like f10 or a bit more….its too short most of the time.
I drool to think what a good 8 inch f9 ish could do.
Gawd I need to finish my 10 inch f8 1/50 wave rms scope !
Starcanoe, from an online thread entitled,Long Slow Newtonians.
I’ve made several 6″ f/9 and f/10 scopes (and even more mirrors). They can provide incredible images if the optics are well figured. I mostly use larger scopes but occasionally pull out 6.1″ f/10 when I need a quality ‘fix’.
Mike Spooner, from an online thread entitled,Long Slow Newtonians.
Mike, I can fully attest to some of the most incredible planetary views and double stars with one of your 6″ f/9 mirrors in a custom made telescope. IIRC, the secondary was only .75″ and the views of Saturn were simply breathtaking. Thanks for having made some of the finest long focal length mirrors on the planet.
Bob S.from an online thread entitled, Long Slow Newtonians.
The 6″ seems like a humble scope size but under the most stable skies it becomes apparent how limiting the atmosphere really is for high definition viewing. I’m more convinced than ever how important accurate figure is for the finest and detailed images. Those breathtaking nights are rare enough that most folks may never get to appreciate what can be achieved. Indeed, there are areas where seeing always limits even small scopes and I feel blessed to live where the veil is often lifted.
Mike Spooner, from an online thread entitled, Long Slow Newtonians.
Snip: Is there a best scope/mount for most of us?
I am a big fan of the AWB OneSky, and I do think that it is the ideal telescope for at least 10% of all beginners. But there are far too many variables for any single scope — or even a selection of 10 different scopes — to be ideal for all beginners.
It’s pretty clear that an 8-inch f/6 Dob for $400 offers more than twice the value of the OneSky for $200. Not only is it much more capable, but it is also much easier to use. The AWB OneSky has good ergonomics, all things considered. But the simple fact is that the Dob design works better for bigger scopes than for smaller ones. Moreover, any off-the-shelf Dob will have a focuser far superior to the OneSky’s helical focuser. And you don’t need to make a light shroud for a solid-tube Dob, as any urban observer must do for the OneSky. And an 8-inch Dob is entirely self-contained, needing no supplemental support.
The extra aperture of an 8-inch Dob is especially important for urban and suburban observers. A 130-mm scope is very capable under dark skies, but extra aperture is a big help in combating light pollution. And there’s a fairly compelling argument that 10-inch Dobs are even better than 8-inchers.
Now some people flat-out can’t afford $400, and others cannot store or transport an 8-inch Dob. For them, a OneSky may be a reasonable compromise. But make no mistake, the OneSky has compromise written all over it.
Many other people may be happier with a small refractor, which is compact, simple, and maintenance-free.
Yet others really need or want Go To. Some who are eager to get started on astrophotography really require motor drive. And so on.
Tony Flanders( Cambridge MA, USA), from an online thread entitled; Is AWB Scope the Best Entry Level Scope for Most Beginners?
The parabolic 130mm f/5s are decent scopes, ones like the Z130 with rings and dovetail are more versatile than the AWB, imo.
A 6in f/8 used newtonian ota with metal rack and pinion focuser on a dob mount should be about 150-200 usd. A more capable all around scope imo, albeit larger and heavier. At f=1200mm and f/8, relatively inexpensive plossls and a 2x or 3x barlow can provide high power magnification.
dmgriff, from an online thread entitled; Is AWB Scope the Best Entry Level Scope for Most Beginners?
I’m still enjoying and using mine, and I do recommend this as a good starter scope. One provision is that the purchaser will need to construct a light baffle for the open truss. I’ve had no issues with the focuser, and mine has held collimation for at least 2 years. The optics are very good, showing detailed and crisp planetary views.
The table top mount on mine was useable, but because I have a Porta II it rides on that most of the time.
SteveG (Seattle, Washington, USA); from an online thread entitled; Is AWB Scope the Best Entry Level Scope for Most Beginners?
It’s not handling a “heavy” eyepiece that I found problematic, it’s getting sharp focus at high magnifications. I have owned more 130 mm F/5s than I can remember. They can be good performers at high (>200x) but generally the focuser is an issue, it contributes to scope jiggle. The plastic upper cages of the doesn’t help. Imagine an 130 mm F/5 with a really good focuser mounted on the Portamount:
This thread is about this scope being the ideal beginners scope. For $200, it’s about as good a good scope as one can find.
But for many beginners $450 is well within reach and an 8 inch GSO Dob not only has the benefits of the greater aperture but the mount is solid and doesn’t require a table and the focuser sets a high standard for affordable scopes.
Bottom line: At the $200 price point, the focuser is a liability. Spend enough to buy an 8 inch with a 2 inch Crayford and you’re getting a more more capable all around scope with a nice focuser that’s a pleasure to use. It sets a high standard mechanically that $200 scopes can’t match.
Jon Isaac (San Diego, California, USA), from an online thread entitled; Is AWB Scope the Best Entry Level Scope for Most Beginners?
Hey, Guys. F/8 is NOT slow. F/8 is normal for a Newt. F/6 is fast. It wasn’t until this plywood-and-pipes-pushalong revolution came about that F/4’s were even considered as a normal telescope (other than the odd 4-1/4″ RFT). The hand-grenade eyepiece market developed only because of the big F/4’s. I have a 10″ F/6 but my 8″ F/8 gets used more.
NinePlanets, from an online thread entitled; Long Slow Newtonians.
In the days of home or domestic mirror making, before the far eastern products swamped the market, F6 was considered fast, F8 normal. Before the SCTs took over F10, only slow Newts were there (and achro refractors). But Moon and planets, + bright stars and objects were the usual viewing menu. However small cats give small FOV as restricted mainly to 1.25 eyepiece views. Newts can have huge focusers and eyepieces by comparison. Big fast mirrors gave the amateur views only observatories once had. But for me the appeal of long FL is using longer FL eyepieces, with longer eye relief and comfort.
25585, from an online thread entitled; Long Slow Newtonians.
My 6″ F8 continues to be my most used scope. If I were stranded on a desert island and could only have one scope, it would be a 6″F8 Newtonian.
Barbie, from an online thread entitled; Long Slow Newtonians.
Frequently the longer slower newt will have a smaller secondary.
Planetary contrast will be improved.
The long slow newt will have significantly less coma. More improvement.
It will also focus sharp much easier. More improvement.
Although a fine adjusting focuser will help this in a fast newt.
You can get to the same magnification in both scopes.
With a barlow(s) or ep’s with built-in barlow, you will reach equal magnification.
Plus the barlow or ep’s with built-in barrows will clean up off axis astigmatism.
Correcting maybe half of the fast newts inherent aberrations in the ep.
If you use a coma corrector, and multi-element astigmatism correcting ep’s, in a fast newt, then you can get really, really close to a long slow newt, on planets.
But the fast newts larger secondary robs some contrast.
Many folks maintain that the multi-element ep’s that work best in fast newts, those rob some contrast too.
The long slow newt, with modest design ep’s, delivers a great planet.
A fast newt of the same size, at the same magnification, needs better ep’s and coma correction to even come close to equaling it. IME
On deep sky targets, at equal aperture and magnification… they’re [e]qual.
Izar187, from an online thread entitled; Long Slow Newtonians.
I have the Orion StarBlast 6…
Under darker skies, it’s great for observing deep-sky objects. Also, given a Newtonian’s total apochromaticism, it’s good for brighter objects, too.
The Orion 120mm f/5 achromat would also be very good for deep-sky observing, but not so much for brighter objects due to the excessive false-colour produced by short achromats when viewing same. Also, there would be no need to collimate the telescope; as there would be with a Newtonian, initially, and on occasion thereafter.
In either event, most DSOs are rather small, so plan on getting at least a 2x barlow, and perhaps even a 3x barlow. For example, I once saw the Trapezium of Orion that made my jaw drop, and with my 6″ f/5 Newtonian. I had used a 12mm 60° eyepiece with a 2.8x barlow, and for a simulated 4.3mm(174x), at the time.
As you can see within my image, above, I quickly abandoned the original Dobson-type mount, and for a tripod-type alt-azimuth.
SkyMuse (Mid-South, USA); from an online thread entitled; 120mm f/5 Refractor or 150mm f/5 Reflector for DSOs?
My 120 f/5 pushed to 120X is a little soft. I don’t think I’ve seen anyone stating that their pulling apo like magnification out of it. That being said, it’s not made for higher mags. It excels at lower power. I never found myself pushing magnication in a fast instrument. I did find it cooled quicker than a 6” f/5, so it was kept and the reflector was sold. Have you considered a 8” Dob? The greater light gathering really helps with DSO’s! Fairly light and portable for what it does. Usually has a good mirror that can take some power.
Deepwoods1 (Connecticut, USA); from an online thread entitled; 120mm f/5 Refractor or 150mm f/5 Reflector for DSOs?
Chicken or the Egg? The Chicken!
Jon Isaacs: I worked in telescope retail in the late 1970’s – early 1980’s. At that time there were no commercially-produced F/4 Newtonians other than Edmund’s Astroscan and Coulter’s little collapsible 4-1/4″ CT-100. (You might come across the odd Cave Astrola or Telescopics Newt/Cass convertible but those were not common.) One exception: Edmund’s big red 8″ F/5 on the fork mount that showed up about 1982.)
At that time, the best eyepieces available for these shorties were orthoscopics and the odd surplus Erfle. Meade supplied a 2″ Erfle too. There were also the Clave Plossl’s from France but they cost a lot of money to import and the best choices were the Meade R.G. Erfles and Orthos and the Brandon Orthoscopics. Even Edmund only supplied their 28mm RKE with the A-scan.
Then along came Coulter with their big blue 13.1″ plywood push-along. I believe that was the first large-ish F/short produced in any numbers. It was about that time that Al Nagler came on the scene with his 1-1/4″ Plossls which were the first of that design affordable by the average telescope user. Then he followed up with his 13mm Nagler design. We called it the “coffee can”. Few could afford one and the kidney bean effect and its weight made it a very hard sell.
At least that’s how my memory has it. Almost all Newtonians commercially produced at that time were F/6 – F/10. F8 was typical. Plossl’s were new and all the rage. (I still use mine, but my Meade R.G’s get the most use.
NinePlanets; from an online thread entitled: Long Slow Newtonians.
I think it’s true that fast Newtonians are pretty much a modern luxury that has made large apertures portable and practical. Back in the day, a 12.5 inch F/6 was quite rare and few Scopes were larger. Today, beginners consider a 12 inch Dob as a possibility.
But the question here is whether the Scopes came about because of availability of the Naglers or vice versa. The eyepieces did become popular with people using all types of Scopes and since the first quality truss Dobs did not appear until nearly 10 years after the introduction of the Naglers, it would seem the eyepieces enabled the development of Premium quality Dobs.
I don’t think the Coulter crew was a big force in popularizing the Naglers. Some years ago I purchased a 13.1 inch Blue Tube and it came with or this and Kellners.
In the last 10 years, something similar has happened. The Ethos eyepieces and the Paracorr 2 have resulted in a move to even faster Dobs . F/3 is the new F/4. The Ethos eyepieces came about as a new design and became popular with owners of all scope types but the Paracorr 2 was designed after Al looked through one of Mike Lockwoods sub F/4 mirrors and decided it deserved a better coma corrector .
From what I know and I have seen , it has been the existence of high quality eyepieces and then the coma correctors that have made high quality, fast Newtonians possible. Obviously TeleVue has benefitted from this shift but they do OK without the Big Dob market .
Jon Isaac( San Diego, California, USA); from an online thread entitled: Long Slow Newtonians.
You know what? Now that my memory is jogged a bit, there were some other sawed-off Newtonians available in ~1980: Meade sold a 6″F/5 on an equatorial mount (their model 645) and there was also an outfit (Star Instruments?) in California that produced a 6″ F/4 tube assembly with Meade accoutrements. Both of these were considered to be “wide field” telescopes but, naturally, coma was terrible and there were no parracor’s around then.
I think it was 1980 that the TV Plossls hit the market. (Coma still sucked.)
These fancy new hand grenade eyepieces truly do make all the difference. They DO allow F/short (under f/8) telescopes to work and big ones to be portable. Al Nagler revolutionized the telescope industry. You’re right. The egg enabled the chicken!
NinePlanets; from an online thread entitled: Long Slow Newtonians.
I owned a Jaegers 6″ f/5 refractor. On DSO’s it was formidable.
But the weakness was magnification. It was great – sensational – using a 35 Panoptic at 21x. But when I put in the 22 Panoptic at 34x – the color and other aberrations were very noticeable, and it only got worse from there. Could have been that particular objective – could be the breed.
The reflector would be a more versatile performer.
Jeff Morgan (Prescott, Arizona, USA), from an online thread entitled; 120mm f/5 Refractor or 150mm f/5 Reflector for DSOs?
I agree with both Starcanoe AND Jon Isaacs. If one has the patience, time, and mechanical ability to set up a 12″ F/5 scope, it’s definitely going to be the better instrument in terms of performance at the eyepiece. However, it will never have the grab ‘n go feel of a 6″ F/10 instrument — which is more likely to be 6″ F/8 these days, but that would shift Jon’s position down to a 10″ F/5, and essentially the same argument.
A 6″ F/8 or higher is a wonderful instrument. In a dobsonian mount, they are truely grab ‘n go as anyone’s 110mm refractor, and much more wind resistant than just about any refractor, period. The coma, tho there, is very, very small, and, I find, genuinely tolerable, unlike F/6, and especially at F/5, where, if you’re using a Newtonian and care about a flat field, you’ve got to introduce a coma corrector, with its inherent weight on the focuser, and unique configuration issue-per-eyepiece, to say nothing of the extra stress on exacting collimation one concurrently moves up to.
For a more refractor-like viewing experience with less fuss, faster cooling, often better performance, the 6″ F/8 newt is an unsung hero in the telescope world. Not the stunning galaxy viewer a 10″ F/5 is, for sure, but more likely to easily split tight doubles than most 10″ F/5 owners can muster. The 10″ F/5 could produce every bit of star splitting capacity a 6″ F/8 could, theoretically, only saying that the average 10″ F/5 owner does not possess the patience, time, or mechanical prowess to make it happen, to say nothing of the extra thermal issues involved with a 10″ mirror compared to a 6″. And the weight of a 6″ F/8 dobsonian is about the easiest “large-sized” telescope to set up a person can find, being amazingly wind resistant, but throwing up consistently good images.
CollinofAlabama (Lubbock, Texas, USA): from an online thread entitled; Long Slow Newtonians.
Forgot one – collimation tolerance. Not a big deal on the Faint Fuzzies, but for planetary detail and close double stars – critical.
Longer focal ratios have a much larger “tolerance envelope” to work with than shorter focal ratios do.
Unless the scope has very well-engineered and beefy construction, the collimation will (not may, will) shift as the scope is moved. There are many mechanical connections where positional shift flexure can manifest themselves, particularly in a truss scope. It takes a lot of attention to detail to get the sources of play under control. And then there is flexure to consider, not just tubes, but focuser boards loaded with three or four pounds of equipment.
Of course, this can be done. My Takahashi Epsilon e-180 is f/2.8 and stays collimated for half a dozen sessions or more. And the 24″long tube weighs 28 pounds without the tube rings.
Jeff Morgan ( Prescott, Arizona, USA); from an online thread entitled: Long Slow Newtonians.
I don’t know about other owners of 10 inch F/5s but I regularly split doubles not possible with a perfect 6 inch . It’s not that much effort . Collimation, a good fan and stable seeing.
As far as collimation shift: I will just say, it is possible to build a fast Dob that does not shift collimation. It might take some time running down the various gremlins…
I often think of Jeff’s 16 inch F/7 with its 112 inch focal length amd his various attempts at making it more user friendly. I’m more than happy with a ladderless 16 inch F/4.4. Ease of use equals more frequent use..
Jon Isaac( San Diego, California, USA); from an online thread entitled; Long Slow Newtonians.
Agree. From my location. Antares skims along the tree tops when at the meridian. Yet I was able to split it with an Orion 10″ f/4.7 in mediocre (5-6) seeing. I couldn’t do it with my 6″ f/9 Starfire which was set up at the same time until the 10″ Newt showed me where to look. IOW I saw it easily with the 10″ f/5 Newt and with difficulty with the 6″ f/9 APO. I’m sure that if the APO were a 6″ f/8 Newt the story would be the same.
Daquad, from an online thread entitled; Long Slow Newtonians.
Hello hawkinsky and welcome to the forums!
I have had a very similar 5″ f5 tabletop reflector and found it to be very useful, particularly for widefield observations of DSO’s. The view of M31/32/110 all in the field is still a favorite.
The problems with entry level refractors usually include a poor mount/tripod combo that make them hard to use and, as above, limited capability for higher magnification.
Neither of these scopes really needs a large eyepiece kit. The value of a 2″ focuser over a 1.25″ focuser is lost on these scopes. The higher weight of a 2″ ep will just exacerbate the shaking of the lightweight mount carrying the refractor.
If it was my $$, I’d get the little Dob and consider adding only 2 eyepieces: an Explore Scientific 68o 24mm and either a Meade Series 5000 82o 5.5mm or an Explore Scientific 82o 4.7mm. (Those can relatively often be found in the classifieds here and at AstroMart for significant savings.) Then find you some dark skies and that gear will give you years of high class observing.
Havasman (Dallas, Texas, USA); form an online thread entitled; 120mm f/5 Refractor or 150mm f/5 Reflector for DSOs?
I had the primary in my Orion XT10i tested and it is actually quite good enough. In my experience, none of the mass market secondaries are much worth a tinker’s **** and the best bang for the buck mod optically is replacing the secondary. A friend of mine replaced his 12″ Orion primary with a Zambuto and later replaced his secondary with an Antares and the verdict was that the secondary made more difference.
Since you asked, my opinion is that of the 4 your listed, go with the Orion or Apertura. A past club president downsized to an Orion XX12g that I have observed with a few times and it is very good, completely stock and breaks down into a handy package.
Havasman (Dallas Texas, USA), from an online thread entitled: Mass Produced Dobsonian Optics.
I think my synta 10″ views are quite good like havasman. I’ve looked at Antares secondaries as well, just haven’t felt the need yet to make the replacement as I’ve only had it a little over 2 months.
Jond, (Detroit USA), from an online thread entitled, Mass Produced Dobsonian Optics.
I don’t think modern mass produced optics tend to have a massive variation these days. At the very least quality control has gotten better in the past few years. I tend to favour Synta (skywatcher) because all of their scopes (4 at this point) I have owned have performed well optically. My issues with them are the manual dob base which is awful for high powered tracking, and the cheap standard focusers. The GOTO dobs are good though.
Smug, from an online thread entitled, Mass Produced Dobsonian Optics.
I can’t speak for the other brands, but I purchased an Orion 12″ scope about 5 years ago. I had budgeted enough to have the mirror re-figured because I wanted it to be capable of really excellent planetary performace.
Much to my delight, the mirror that came in the scope was far better than I had expected. I do a lot of star testing using Suiter’s methods, and here is what I found: No turned edge, no zones, and while not premium level of smoothness, still surprisingly good. A 33% obstruction test for spherical aberration was almost perfect. At 10 waves of defocus, it was almost impossible to see any size difference in the secondary shadow size and the breakout was to close on either side to be easy to see. I was very impressed with the quality and decided that there would be little practical improvement to be made by sending it to someone for re-figuring.
Planetary views with this scope are spectacular. Side by side, my 6″ Apo really could not keep pace, and in fact, I had better Jupiter views in this scope than in my C14 (which was not a bad C14, but not of the same quality as the Orion).
This is not a premium quality mirror, but it is quite excellent. I don’t know if this is typical or if I got lucky, but this telescope gives the best planetary views I have ever had.
Ed Moreno(Eddgie), from an online thread entitled, Mass Produced Dobsonian Optics.
The primary on my 10 inch Zhumell (aka Apertura) is very good as far as I can tell through a star test. I’m sending it off to Steve Swayze soon for legit testing but I think it will fair just fine. I will also be replacing my secondary with a 1/20 wave Antares, not even going to bother testing it, just replace it.
Muddman97(NE Oklahoma, USA), from an online thread entitled, Mass Produced Dobsonian Optics.
That pretty much sums up what I’m looking for (good assessment). Best bang for the buck – I’m not looking to spend three times the money for only a 5% improvement.
10001110101 (SE Ohio), from an online thread entitled, Mass Produced Dobsonian Optics.
I had the mirror from my Apertura 12AD tested when i converted it to a three strut. I was pleasantly surprised to find out it was an excellent mirror that didn’t need any work period.
Old Rookie (North Central Ohio, USA), from an online thread entitled, Mass Produced Dobsonian Optics.
Meade mirrors are GSO.
You forgot SkyWatcher, which is another Synta brand.
The focusers on the Meades, Aperturas, and Explore Scientifics are better than the Orions and Sky-Watchers, IMO.
Smoother and more easily adjusted and easier to use.
The mirror cells on all of the scopes are decent in 10″ and larger.
As for movement on the axes, I favor the Explore Scientifics, since they have borrowed from high end scopes.
And this is true whether you get a tubed or truss version.
The Explore Scientifics also allow placement of the focuser on either side, whatever your preference.
As far as performance, goes, all are made in a bell-shaped curve. Your odds are good to get a halfway decent mirror, but your odds are low that you will get either a complete dog or a superb mirror.
(the best 16″ mirror I’ve ever seen was a GSO, BTW).
Starman1( LA, USA), from an online thread entitled, Mass Produced Dobsonian Optics.
It’s no longer the 80’s and 90’s where mass produced mirrors were hit or miss. Now days and it has been like this for the past 15 years, Synta and GSO mirrors are of good quality. They have high tech factories that can pump out consistent quality mirrors. The mirrors are fantastic optically and anyone would be proud to own one. These two companies have revolutionized amateur astronomy. Now you can buy an affordable telescope with optics you can trust.
Are they as good as premium optics. No, but you will have to know your stuff and look hard to tell the difference. The mechanics and motions of premium scopes are larger advantages than optics verse mass produced.
Now in our hobby we have a choice between great and excellent. Junk and risk has largely been eliminated from the market.
dongallo (KnoxvilleTN, USA), from an online thread entitled, Mass Produced Dobsonian Optics.
I had a Cave Astrola 10″ F8 and a GSO 10 ” F5 side by side and they both stood up well to high magnification on the planets. No serendipity here, just extensive testing. Perhaps your predjudice towards premium scopes has clouded your vision!! I also had a chance to directly compare an Orion 10″ XT to a Zambuto of similar aperture and they BOTH showed the same amount of detail in Jupiter’s cloud bands at similar magnifications. Both were properly cooled and collimated and both seemed to have good mechanical construction that didn’t interfere with high magnification planetary performance so Yes, I would say the mass produced scopes have gotten a lot better. You and others on this forum have the attitude that a scope has to be premium to deliver outstanding image quality and that simply isn’t the case!!
Now we can consider this horse sufficiently beaten to death!!
Barbie, from an online thread entitled, Mass Produced Dobsonian Optics.
I had an Orion XT10 in the past and a 8 inch dob now. Both provide amazing planetary views. A 10 incher is a great all around scope.
Steve D.(Woodstock, Georgia,USA); from an online thread entitled; A 10 inch Dob- good enough?
I’m personally not a fan of the typical commercial 10″ Dobsonians. The amount of aberration is just too much for me unless you plug in a coma corrector or use premium eyepieces.
I find the 8″ Dobsonians much more pleasing due to the somewhat slower optics.
Olecuss, from an online thread entitled; A 10 inch Dob- good enough?
The most important factor is the seeing, the stability of the atmosphere. But in my experience , given good seeing, my 15 year old 10 inch Taiwanese Dob outperformed my 120 mm Orion ED refractor . For a 120 mm , the 120mm Eon did a very good job but the increased resolution and contrast transfer of the 10 inch was too much for it. Comparing a 5 inch reflector with a 10 inch will be even more dramatic.
Jon Isaac(San Diego, California, USA), from an online thread entitled; A 10 inch Dob- good enough?
Actual view thru an 8″ Reflector …
mvas( Eastern Ohio, USA), from an online thread entitled; A 10 inch Dob- good enough?
Yes. A 10″ is plenty of aperture. IMO. Planets will show plenty of detail to keep you busy including the GRS, Martian polar caps and maria, Saturn and it’s rings are stunning, and much more. Your local seeing conditions will determine how much is seen on a given night.
Get the Dob, even if it means using your 130 for a while. Spend the time training yourself to get the most from a smaller aperture. The experience will pay dividends when you get the 10″.
Asbytec(Pampanga, Phillipines); form an online thread entitled; A 10 inch Dob- good enough?
10 inch Dobs will be a lot heavier than a 5 inch. Negociate for an 8 sooner, + some eyepieces. An 8 inch F6 would be fine for Moon and planets. Then you can save for a 12″
Actually, I tend to agree, except I’d go for an 8″ F7 as it’s much lighter and easier to set up and collimate than a 10″ F6. A quality 8″ aperture can provide devastatingly good planetary views. The trouble is that F7 focal ratio is not very common and would more than likely be custom.
Jeff B, from an online thread entitled; A 10 inch Dob-good enough?
Careful! You’re asking for advice from many of those who have been infected with aperture fever!
I think the best 6″ f/8 is an 8″ f/6, and of course a 10″ has 56% more light grasp than that… and a 12″ might be enough for the fainter DSO’s….
Actually 10″ is a very capable scope and still quite portable for the reasonably fit. A tube for a 10″ f 4.7 fits neatly across most automobile rear seats too.
jtsenghas (Northwest Ohio, USA); from an online thread entitled; A 10 inch Dob-good enough?
A 10-inch Dob is a great instrument, but I think the advice on seeing conditions and bringing your Dob to thermal equilibrium mentioned earlier in this thread cannot be stressed enough.
I live in southern New England where the skies are unsteady much of the time. On those few nights a year when skies are dry, clear and steady (and the moon is not present), you can get very good planetary views with even an 8-inch Dob and a quality 6mm EP. We’re talking cloud belt swirls and transit shadows on Jupiter, an easy Cassini split on Saturn, and the polar cap and some surface features on Mars. On nights with unsteady seeing, I like to say it’s like looking through a pot of boiling water.
You will have to determine if the added weight, collimation, and cool-down of a 10-inch is worth the effort vs. a smaller aperture given the typical seeing under your skies. If your skies are relatively dark and steady, I’m sure the views will be tremendous.
tmichaelbanks(New England, USA); from an online thread entitled; A 10 inch Dob-good enough?
I had my 10” Skywatcher solid tube Dob out this morning and the Orion Nebula was outstanding. So was M41 on Canis Majorum. Last week Mars showed a ton of detail at 170X.
You’ll love the 10” Dob.
Sandy Houtex( Houston, Texas, USA); A 10 inch Dob-good enough?
When seeing is only mediocre, a 6″ does have an advantage that conditions are more stable due to the smaller “tube of light” being used. 6″ is also a decent aperture for the brighter objects.
Still, 10″ is a lot better for resolution and light grasp when conditions permit. Oh, so many DSO can’t be appreciated until you make at least that step up.
Aperture fever can peter out though for the work involved with managing the really big scopes, and I now some older folks step down to 8″in their later years to reduce the physical work involved with setup and teardown. For anyone reasonably fit I think 10″is just right!
jtsenghas, (Northwest Ohio, USA); from an online thread entitled; A 10 inch Dob-good enough?
I concur with most people here, 10″ is indeed a great size!
I consider 10″ as the “compromise size” in dobs, being the perfect compromise of portability and aperture. If you go much smaller you too often feel the limits of your light gathering/resolution power (usually on DSOs), but if you go bigger transport/potability/setup start to become significant considerations. 10″ is the happy medium.
JoeBlow(Australia); from an online thread entitled; A 10 inch Dob-good enough?
Realistically how easy is it to track say Mars at 200x with a Dobsonian?
Are there many people here who are able to use a Dob for planets while making planetary drawings?
I find it very hard to make sketches of planets with my alt-az mount (Vixen Mini Porta) and slow motion controls. I would even find it harder with a Dob.**
Magnetic Field (UK), from an online thread entitled;A 10 inch Dob-good enough?
It depends on the scope as well as the operator. I have no trouble tracking Mars at 400x manually with my GSO 10 inch Dob.
On the other hand, if Mars were the on the table in front me, I couldn’t make a sketch of it.
Jon Isaac (San Diego, California, USA); from an online thread entitled; a 10 inch Dob-good enough?
Get the 10″! It is a good aperture for all objects and is at the limit for reasonable portability.Under dark skies, it will reveal quite a bit. Prior to the dobsonian revolution a 10″ was considered a monster fantasy scope by most enthusiasts. It will not disappoint-that is until you get the strange affliction called aperture fever. That being said, a 10″ will serve you well even if you go bigger in the future and if you dodge the fever, it will provide a lifetime of satisfying viewing.I know I still use my 6″ even with a larger scope on hand.
aat (Connecticut, USA); from an online thread entitled; a 10 inch Dob-good enough?
I have now tested quite a few Chinese mirrors using Bath interferometer. About half a dozen 12″, many 8″ and two 16″. Not a single one was below 0.8 Strehl (well one 8″ was just marginal), with a few above 0.9 (including a 12″ and a 16″), one well above 0.9 and a vast majority between 0.8 and 0.85 .
From this admittedly limited sample I’d say that whatever method Chinese are using (manual labor or CNC polisher) they very consistently turn out diffraction limited optic. At prices they sell them, I would say a small miracle actually. I have also tested a few flats, and there you actually can find a true lemon (I bought two 70mm flats and they are both bad (not catastrophic but obviously astigmatic). This is also tested properly, by interferometer (Twyman-Green). Most flats that end up in an OTA seem decent.
What I have also found is that they consistently put best optic into best/most expensive line (BlackDiamond or whatever), and worst optic seem to be reserved for ATMing (sold as optics parts, no OTAs). So they KNOW what each optics is like, which tells us they must use reliable metric (that Zygo shown in GSO video is not a fake!).
PS this is all relatively recent stuff, GSO/Synta made with various branding. A few years back some of the Chinese telescopes were true abominations. One 8″ f/4 set (I still have it) has nearly spherical mirror (with about one wave of astigmatism thrown in), and secondary was so bad that I think they simply used window glass, cut an ellipse and aluminized it. This is “no brand” scope with plastic focuser and a hammertone-like green tube. If you see one of those, stay well away!!!!
PPS I have also tested a Zambuto 8″ f/6 using Bath IF; it came out with a 0.98+ Strehl !
But keep it in perspective. This image was done by my friend Mark with a run-of-the-mill 12″ GSO – solid but not exceptional (I think it tested about 0.87 Strehl (*)). Yes, that is detail on Ganymede !!!
(*) just found a report on Mark’s 12″ GSO; it measured 0.86
bratislav (Melbourne, Australia); from an online thread entitled: Zambuto/Royce vs Synta/GSO.
<< This image was done by my friend Mark with a run-of-the-mill 12″ GSO – solid but not exceptional (I think it tested about 0.87 Strehl (*)). Yes, that is detail on Ganymede !!! >>
Incredible. Very impressive indeed !
Chucky, from an online thread entitled: Zambuto/Royce vs Synta/GSO.
In my mind, the ideal planet telescope is a 10 or 12″ EQ Newt (split ring?) in a permanent location with a clear view of the south and overhead. Add a good binoviewer, pairs of long ZAOs, and an easy way to reach the EP, and I’d be all set. In reality, it would be too expensive and I have no place to set it up permanently. So-o-o-o, I’ve arranged to buy a used 8″ f/8 EQ-mounted Newt. I’ll need to have some servicing done on the mirrors. I’m thinking that within the realm of likely possibility, this may very well be my ideal set-up. Right now it has no fan and a tall R&P focuser, so I may change those things. And I’ll built a cart for the Meade RG mount. I already have a tall adjustable chair and a Denk II with pairs of TV Plossls.
Deep 13(NE Ohio, USA), from an online thread entitled, Ideal Planet Scope
Actually, I had had the good fortune to view through 2 separate 8-inch f/8 reflectors. Each one had optics ground and polished by the owner. Unbelievable! These guys did an amazing on their respective mirrors. Jupiter at the Mount Kobau Star Party in Aug. 1985 I will never forget!
Neither will I forget the Oct. 1988 opposition of Mars through Lance Oklevic’s 8-inch f/8 self fabricated newtonian reflector. It was a Sat. night, I believe, and Terence Dickinson gave a Mars lecture in the auditorium at the H.R. MacMillan planetarium. Afterwards many amateurs set up their scopes on the large concrete entrance to the Gordon Southam Observatory. A member’s AP 6-inch f/8 Apo was also pointed towards Mars.
So yes, an 8-inch f/8 can make an ideal planet killer!
RalphMeisterTigerman, from an online thread entitled, Ideal Planet Scope
My ideal planetary scope would be the biggest, longest newtonian I could afford – biggest aperture, smallest central obstruction.
In practice I have a 12″ F/5 on an NEQ6 which I occasionally use for visual, it’s great but also a giant pain in the **** – the EP is 2′ above my head in most positions and I don’t like standing on wobbly ladders in the dark, and it’s a bit awkward to mount solo. Once it’s set up I prefer it to my 14″ dobsonian since I think it gives better views and the computerized mount is a million times better than tracking by hand, but the dob gets more use because it’s much less hassle.
Smug, from an online thread entitled, Ideal Planet Scope
I owned a Meade 12.5 inch F/6 RG for a number of years. Honestly, for large Newtonians, GEMs are a pain in the rear.
– In getting good planetary views, seeing is the number one priority. It all starts with the seeing. One wants a scope of sufficient aperture than on a good night, it is not limited by it’s aperture.
– In terms of planetary contrast and detail, aperture is more important than focal ratio. This is particularly true for scope on a tracking mount. Pick a focal length that is ergonomically acceptable, pick the largest aperture that is affordable.
– Important are high quality optics.
– Thermal management is critical.
– The mechanical structure must be stable and free from vibration.
– A small secondary is of some consideration but a little bigger than the minimum means alignment is easier, the illuminated circle is larger and any edge issues with the secondary are of less significance.
My best views of Jupiter and Saturn were with “Junior”, my 25 inch F/5 Obsession. The seeing in the high desert where Junior lived was rarely more than average so such views were few and far between. Our home in San Diego is often blessed with very good seeing and at time excellent seeing, under an arc-second is relatively common. A scope that big is not practical. For my backyard, this is what I consider my best planetary scope.
– 13.1 inch F/5.5 Starsplitter with a Robert Royce mirror. It is a robust scope for a 13.1 inch, it’s heavy but stable, the secondary is right at 20% and it has Feathertouch focuser. It has enough aperture for the really good nights while still being ergonomically comfortable.
– Tracking: I parted ways with 12.5 inch Meade RG when I acquired the Starsplitter. The Starsplitter was a package deal which included a Tom O, dual axis aluminum Equatorial platform. For visual observation, I think EQ platforms are superior to GEMs. A good one is rock solid and retains the superior ergonomics of the Dobsonian. The mount is rated for a 16-18 inch and yet weighs less than 30 pounds and can be carried in one hand. Truthfully though, I actually prefer manual tracking, I like the intimacy and the issues with nudging don’t arise until well past 400x.
My backup planetary scope is my 10 inch GSO Dob. I’ve had it for 15 years, it has good optics and it’s a quicker setup. I had an Orion 120mm Eon ED/apo for a couple of years but I found the 10 inch Dob was enough better on the planets and double stars that the Eon just sat in it’s case so I sold it. The 10 inch on the dual axis EQ platform.
I think that matching the scope to your local conditions is important. I am about 4 miles from the Pacific Ocean and generally south of the jet streams. The flow off the ocean can mean very good seeing and so in general, I have good seeing enough of the time that I do not need to fight it because there will soon be another night.
Jon Isaac(San Diego, California, USA); from an online thread entitled, Ideal Planet Scope
First, I would not go with a split ring Newt for exactly the reason Jon mentioned. If you wanted that option for tracking, just get a Go2 Dob or a tracking platform. Split ring Newt can put eyepiece in just horrible location.
A 10″ f/6 sounds great, but to get the small secondary (5mm fully illuminated field) it will be no better than a 12″ f/5 with the same size fully illuminated field. In other words, you get a scope in the 10″ f/6 that is as good for planets, but not as good for just about any other use (mirror quality being equal). The 10″ though would be lighter and easier to manage. I have a 12″ with a fine mirror that delivers outstanding planetary views, but it takes a hand truck to move it (though it is easier to move than my 6″ Apo on a GEM mount was by many orders of magnitude!)
The major issue with either of these is that depending on your location, seeing may limit both of these to working at less than their full capability on both nights, and the 12″ will suffer a bit more than the 10″.
Adding boundary layer fans will up the weight of both, but since the weight of the 12″ OTA is already pushing 50 lbs, adding fans is just that much more to handle. The 10″ could be kept under 40 lbs with fans and will be easier to boundary layer scrub (and with with boundary layer fans, cool down is going to be far less of an issue because boundary layer scrubbing means you don’t need to cool the mirror.
I think there would be fewer occasions where the 12″ would outperform the 10″ if you live somewhere with poor seeing, but if you live somewhere with lots of excellent seeing, 12″ will just be a better all around scope and unless the only use for the instrument is planetary, then the 12″ to me seems to be the way to go. While the OTA will be 50 lbs, this is still manageable by many people, and if it is not manageable by you, then I would think that we would not be having this conversation.
A highly optimized 10″ though would probably keep up, but only at the cost of loosing some of the all around capability of the 12″. Again, if only use is planetary, a highly optimized 10″ would be hard to beat on a night of typical seeing for many. But only hard. Not impossible.
Eddgie, from an online thread entitled; Ideal planetary Scope
The Newtonian has some inherent advantages that make it the prime candidate for a planetary scope. It is very simple, there are only two optical surfaces. Those two components can be made essentially perfect . Large apertures are very doable so they do not suffer the limited resolution and fine scale contrast of smaller aperture scopes . Very small central obstructions are possible.
The potential is there. As with any instrument , the challenge is in the execution and in the operation .
Jon Isaac (San Diego, California, USA), form an online thread entitled; Ideal planetary Scope
This is my planetary telescope.It is a Mikage 210 mm F/7.7 Newtonian on a Pentax MS-5 GEM. It gives great images of the planets through my 7mm Pentax XW EP
Stephen Kennedy( California, USA), from an online thread entitled; Ideal planetary Scope
I’m glad you posted the photo of your scope. When I wrote:
“The potential is there. As with any instrument , the challenge is in the execution and in the operation .”
I had your scope in mind.
Jon Isaac(San Diego, California, USA), from an online thread entitled: Ideal planetary Scope
I agree with the view that aperture is key, but the cooling is a biggie too.
About a year ago I acquired the parts for a 8″ F7 Newtonian. The mirror is a 20mm thick quartz made by Zambuto, and the secondary is tiny. I forget the dimension, but this scope is optimized for high powers/planets.
The first time I got a good view of Saturn with this scope I was seriously impressed. Compared to a nearby 18″ Obsession, the little 8″ was showing a much sharper and more stable view (this was after several hours in the field).
The quartz primary is the key with this thing (well, apart from the fact that the quality is superb). This scope actually produces stable images more rapidly than my 80mm triplet refractor.
The only thing holding this scope back is that it is only 8″.
areyoukiddingme, from an online thread entitled; Ideal Planetary Scope
My best planetary view was many years ago looking at Jupiter through someone’s 18″ Zambuto mirror dob with a Televue binoviewer. Tak LE eyepieces of unknown focal length. At the time I didn’t have a lot of experience to ask more questions or to know if the seeing was unusually good. I don’t recall the magnification, but I would now estimate 350x or higher going by memory. A lot higher than I normally use now. It was driven. Cooling fans I don’t know. It was in Joshua Tree National Park, an area not known for great seeing, but it must have been pretty good that night. That evening I went back to my own un-optimized 16″ scope and realized I had a lot to do to catch up!
A club member has an 8″ f/8 ATM dob, and it works well. Trapezium and the E and F stars were very sharp one night with better than average seeing night here in the inland area of S. California. I think the 8″ f/8 dob would be a great scope for you.
MikeRatcliff (California, USA); from an online thread entitled; Ideal Planetary Scope
My best planetary views have been through my 20″ f/5 Obsession with a Galaxy mirror. Mars was best with the scope further south in frequent stable seeing (500 to 750x). I have had some of my best views of Jupiter and Saturn through it here, despite seeing that has not been as good for planets and has topped out around 357 to 417x on the best nights…but it is just idling because of the seeing. I would like to get the scope back south again to do some of the things I planned, like an albedo map of Ganymede.
I made an off axis mask that gives me 8″ of unobstructed aperture in the least thermally disrupted part of the mirror, but I find the full 20″ aperture provides more detail on nights that are worth observing planets at 250x or above.
A very large Dob in excellent seeing would be very difficult to top…particularly in the southern hemisphere with the planets high overhead.
Redbetter(Central Valley, California); from an online thread entitled; Ideal Planetary Scope
I have an 8″ F/8 home-made Newt (traditional Parks tube, mirror by me, smallish secondary, etc). I’ve used it a few times side-by-side with an Astro Physics 6″ F/12 triplet and an old Cave 8″ F/6. Several of us could see no difference in the views of moon and planets in the 3 scopes.
Goerge N ( New York, USA); from an online thread entitled: Ideal Planetary Scope
Late to the thread with my $0.02, but I’m with Redbetter in post #63. I typically experience exceptional seeing only a few times a year here in southern New England, but when the good skies do arrive my pedestrian XT8 provides some great planetary views: swirls in the belts and crisp transit shadows on Jupiter; clear, dark Cassini Division on Saturn, polar cap and reasonable surface markings on Mars. I suppose more powerful scope configurations would do better, but I find the old saw about “no substitute for good seeing” usually rules the night.
tmichaelbanks; from an online thread entitled: Ideal Planetary Scope
Check out this graph of Modulation transfer: (from Suiter….)
Now, it is for comparing a 10-inch unobstructed optic to a 12-inch 20% obstructed optic. But the curves look exactly the same for a 5 inch unobstructed vs a 6 inch 20%. ( The cycles per arc second numbers at the bottom will have to be reduced by 1/2 as well…) You can scale the diagram for any two apertures where one is 1.2 times bigger than the other….. (3″ vs. 3.6″, 4″ vs. 4.8″, 5″ vs 6″, 6″ vs. 7.2″, 7″ vs 8.4″, 8″ vs 9.6″…….) Scale the numbers at the bottom as well…
What does it say? It says that a an unobstructed scope of aperture X cannot keep up with a 20% obstructed scope of aperture 1.2X at any spatial frequency you care to name. The bigger, obstructed scope will have better resolution and transfer more contrast to the eye.
The ‘one-inch-bigger’ rule of thumb is not really true if the central obstruction of the larger scope is 20% or less.
Enjoy your popcorn!
Cotts( Madoc, Ontario, Canada): from an online thread entitled: Mak-Newt vs. Apo Refractor?
In my own search for the “best planetary scope” I bought and sold over 100 telescopes of most every design. As I would pick a winner, I would find a new challenger and do yet another side-by-side comp. Having the scopes under identical seeing conditions and owning dual sets of Pentax SMC orthos, and now Zeiss Abbe Orthos (4-34mm) helped keep the comps as fair as possible. While I read the theoretical differences I personally prefer seeing the images.
Many of my best views have been through Newtonians. To me the 8” Newtonian is the unsung hero of backyard astronomy. To this day my most memorable view of Mars was through a 10” Portaball. As Jon said, seeing is the key and I happened to hit a night of near perfect seeing with the Portaball. After that experience I bought a larger Portaball because I agree there is no substitute for aperture IF the optics are very good to excellent and supported by seeing. At the same time I was climbing the aperture ladder with refractors which topped out at a D&G 8” f/12 for achromats, and my current TEC200ED though I did get a chance to view through Al George’s 15” D&G along the way.
Over the years I found I prefer refractors. Please do not read that as stating they are better because I have had simply stunning views through Newtonians, Dall-Kirkhams and Maks. But ergonomics factor into my preference too and I prefer being seated with a binoviewer to standing on a ladder. For the last two months I have been comparing the TEC to a a 1960s Cave 12 3/4” Newtonian with arguably the finest mirror Cave ever produced, and Quartz to boot. When the seeing permits, and the big Newt is cooled to near ambient it clearly beats the TEC. Deeper color saturation and finer detail on Jupiter and Saturn. But I am up a ladder three steps at zenith and have forgotten that fact once or twice….
While aperture – with supporting seeing – wins, people who have never used big scopes do not see the downside. Big scopes are heavy, at some point exceed one-person set up, and demand correspondingly large mounts and, preferably, permanent installation.
My most used scope this last year has been a Takahashi FC-125. Why? Superb images, easy set up, and it matches seeing consistently. At the moment I do not have a 8” Newtonian, but if I did it would be right in there too, especially one of f/7 – f/8 focal length. I am going to build an observatory this year and will permanently mount the TEC with a smaller refractor piggybacked so I can cover all seeing. And the 18” Starmaster will be the deep sky partner.
Itha(Bend, Oregon, USA); from an online thread entitled: Ideal Planetary Scope.
Let us consider seeing, optics, mount stability, eye relief and exit pupil, and comfort:
(1) seeing. Seeing is too often the limiting factor. The “best” planetary scope will have an Airy disk small enough that the view is dominated by seeing. In mathematical terms, the system (optics+seeing) Airy disk FWHM (“full width at half maximum for the central peak) will be ~ < 110% of the optics Airy disk, or the Airy disk FWHM s/b about x0.45 your best-case seeing or less. Now when we talk seeing in visual terms, we talk about seeing over the time scale of the persistence of the eye, about 1/15th of a second. If the best seeing you generally encounter is about 1 arcsec, you need an Airy disk FWHM ~ lambda/D ~0.4 arcsec (8″ aperture), and so on, where lambda is the wavelength (0.55um is about right) and D is the mirror (yes, mirror!) diameter. This will set the optimum size for your optics. In general, for the vast majority of us, this would be an aperture of about 8″-16”,
(2) the way to think about optics quality for the planets is by examining the optics system modulation transfer function, or MTF. The MTF is the Fourier transform of the optics point spread function. Graphed, the abscissa is spatial frequency (the inverse of resolution). That is, zero spatial frequency, 0 lines/mm, is a resolution of infinity while high spatial frequency represents very fine resolution. The ordinate is contrast, which is always a value of between 1 and zero. At zero spatial frequency, the contrast is unity for any optical system, so the curve starts at unity in the upper-left hand corner. At very high spatial frequency, the contrast asymptotically approaches zero. Contrast of features for extended sources such as planets (as opposed to point sources like stars) can then be determined by examining the equivalent spatial frequency for that feature.
Now for a perfect, unobstructed Airy disk, there is a curve descending from unity at zero spatial frequency to zero as you move to the right along the abscissa. All optical systems are imperfect to some degree, however, and thus the curve for your system will lie slightly below the “perfect” MTF curve for most spatial frequencies. Now to get more quantitative: the MTF decrease for a circular central obstruction of 15% is hardly noticeable, at 20% it is noticeable but small, and decreases rapidly from there with increasing central obscuration. Few observers would notice much difference between the 15% and the 20% obscuration but, for a planet killer, that should be the limit. Note that this is slightly larger than the secondary size due to the slightly larger diameter secondary holder. For example, my 10″ f/6/6 telescope utilizes a 1.83″ minor axis (which installed at a 45 deg angle corresponds to a circular obscuration of the primary) but the secondary holder is in fact 0.193″ in diameter. Thus, my telescope meets the 20% criterion. Could I instead install the next smaller 1.52″ “standard” size secondary for even smaller obscuration? Sure, but I would be vignetting significantly at the field edge for powers lower than about x180. I also like to look at DSOs, so this is would not be a good trade for me.
What about geometrical aberrations, such as spherical aberration and coma? These can rapidly drop the MTF curve. This is why it is important to have very good optics, and I mean a total system peak-to-valley wavefront error of less than 1/4 lambda (again, 0.55 um is a good visual wavelength average). The secondary mirror will contribute too, of course, as would any corrector plate. Note that, due to the tilt, the secondary mirror aberrations of a Newtonian can be reduced by 1/SQRT(2). To get the total system peak-to-valley wavefront error, RSS the optical component errors. For example, suppose the primary is 1/8 wave at the (HeNe laser) interferometric wavelength of 0.63um, and the secondary is similarly 1/10 wave. We then have a total peak-to-valley wavefront error of 0.63um/0.55un * [SQRT ( 1/8^2 + (1/SQRT(2) * 1/10)^2 ] = 1/7 wave. “Diffraction limited” is often considered to be 1/4 wave for the total system, so the system in this example is diffraction limited. However, 1/7 wave of aberration will drop the MTF curve noticeably, so it is not ideal. What is ideal? A total system wavefront error of better than 1/10 wave comes very close, and is probably indistinguishable from perfect. My personal 10″ Newt has a total system peak-to-valley wavefront error at 0.55 um of 1/16 wave, making the deviation due to geometrical aberrations from the diffraction-only MTF curve indiscernible. Incidentally, I am assuming you know how to properly collimate your scope.
(3) mounts and comfort: a poor mount is a PITA, right? A good mount for planets will do the following:
–hold the image steady at high power (x50 the aperture size in inches),
–place the eyepiece in a comfortable viewing position,
–not break your back to set it up,
–for those of us who hate “nudge-nudge-nudge,” track well enough to keep the planet in the field of view, and
–for those of us who hate ladders, not place the eyepiece position above standing.
A GEM with a decent drive (like those equipped with Byers or Opti-Craft machining gears) can satisfy all these needs provided the telescope focal length is short enough to keep the eyepiece position at or below eye level. As luck would have it, most of us cannot reach the eyepiece at telescope focal lengths of about 65″ (GEM) or 70″ (Dobsonian). For the latter, subtract the d’Artume tracking table height, so you also end up with about 65″. Now it is very difficult to obtain and properly secure a mirror while maintaining system optical quality of 1/10 wave P-V (peak-to-valley) or better at f/ratio < f/4.5. Dividing 65″ by f/4.5 yields a maximum mirror diameter of about 14″. Happily, this happens to about match the largest telescope we can use even in “ideal” seeing conditions.
Thus, for those who wish to manhandle a 14″ telescope (or mount it permanently), who have occasional excellent seeing at their primary observing site, pay up for excellent optics (or make your own), and who also take great care with their mirror cell and system collimation, a 14″ Dob telescope with a tracking table (d’Artume table) is about the maximum aperture for the best planetary viewing experience.
A GEM with 2″ and above axes will also work for such a telescope but, really, it needs to be permanently mounted. I’ve found a 10″ is about the maximum one can mount on a GEM with 1.5″ axes (the maximum mount size that can be rolled and is transportable) w/o stability problems, and an electric focuser helps, too. I am easily able to roll mine out on casters from my garage to my backyard concrete patio.
So there you have it: for those of us with pretty good but not great seeing, a high quality 10″ telescope on a GEM with rotating rings (mandatory for comfort) would be ideal. A 12.5″-to-14″ tracking Dob would be even slightly better if seeing permits.
OK, why not a 14″ Cass or a SCT? Both have larger central obstructions that diminish MTF, and the commercially readily available SCTs rarely have good enough optics. What about a refractor? Aperture-for-aperture, a high-quality APO (almost no lateral color) refractor will be the best of all BUT the Airy disk of a 12″ scope is HALF the width of a 6″ refractor and trounces the 6″ perfect refractor MTF curve. Go larger and refractors have problems: with lateral color correction, with mechanical distortion of the heavy lens elements, and should I mention … cost?
(4) let us not forget our eyes. For those of us who are a bit older, we’ve probably accumulated a number of floaters in our eyeball fluid over many years. The result: these can become really annoying when the system exit pupil (= focal length of eyepiece/focal ratio of telescope) decreases below about 0.5 mm. Choose your magnification accordingly. Also, good eye relief is wonderful. For these reasons, my favorite high power eyepiece for my f/6.6 telescope is the 20mm eye relief 3.5mm Pentax XW.
Happy observing always.
dhferguson, from an online thread entitled: Ideal Planetary Scope.
I have a 10 inch F10 Newtonion that I made many years ago , I made everything myself bar the Antare’s 1 1/4 inch low profile helical focuser and 3/4 inch secondary on its curved spider (no diffraction spikes ), its a beast as the OTA is over 2500mm long and weighs 30kg + ! but I have yet to look through any telescope at this size that best’s it on the Moon and Planets !! it shows the same detail on Jupiter as our club’s C14 easily and sharper and kills a friends Meade LX200 10 inch SCT that ain’t no slouch .
But again the Newt is a LARGE telescope ! .. Like a 10 inch F10 APO with awesome views from the top of a 5 foot set of stairs when viewing above 70* .
Beanerds(Darwin, Australia); from an online thread entitled: 6″ Newt vs. 8″ SCT.
I have a good 6″ F6 Newtonian and a good Celestron C8, other than general better star images and potentially wider FOV in the 6″, overall the 8″ is superior. A comparison with a good 8″ Newtonian I would expect to be a different matter.
Peter Drew (England, UK), from an online thread entitled: 6″ Newt vs. 8″ SCT.
I made the jump from a Orion 8″ to a Skywatcher 14″. It provided vast improvements in planets/moons, faint reflection nebula, and distant little galaxies. But mainly just increased the amount of objects I could identify…
I was a little disappointed in the little improvement in galaxy detail. Objects like Bodes Galaxy went from a fuzzy ball in my 8″, to a fuzzy ball with a hint of arms in my 14″.
I would say forget about the 10″, you wouldn’t notice the difference.
The 12″ would improve Jupiter, Saturn and allow you to chase the fainter moons. If you have a very dark site, the 12″ will bring more objects into view and provide a some improvement on large galaxies.
You can never really upgrade from an 8″, it is the perfect blend of size and power. If you want a second scope go for a wider field (nice pair of binoculars and a mount) or save up and get the biggest beast you can fit in your car.
Luca Brasi; from an online thread entitled: Aperture Fever? 8″vs 10″ or 12″
+1 on moving to at least a 12″ from an 8″ That’s a 125% gain or about 1/2 to 2/3rds magnitude gain.That will give you more detail on the brighter objects you can already see with the 8″ and you’ll see faint fuzzes in the 12″ that are invisible in the 8″. Lunar and planet detail / color will increase substantially as well.
Cosmophil(So. California, USA); from an online thread entitled: Aperture Fever? 8″vs 10″ or 12″
In all seriousness though, I think Jim Waters and Astro-Master have the right idea. I also enjoy DSOs and Lunar. While my 11″ Teeter is extremely good, and certainly shows more than my TEC180, it was my Teeter 16″ that really opened up the sky for me in a way that the other scopes couldn’t.
As others have said though, weight and manageability become much more of a consideration at the 16″ size than say a 12″.
And why isn’t my Teeter 16″ in my signature? I sold it! I have given my allegiance to The Dark Lord and am awaiting completion of my SpicaEye 24″. Yes, I am a zombie.
Codbear(Novato, California, USA); from an online thread entitled: Aperture Fever? 8″vs 10″ or 12″
The difference in views going from 8 to 12 will generate a “wow,” so will the difference in weight. A few pounds that might seem insignificant when reading about them in the catalogue become much more significant in use, so I’d wouldn’t recommend replacing the 12 with the 8 unless you find the 12 EASY to manage because telescopes seem to get much heavier to me after the new wears off. Over time, the visual WOW becomes wow, and the weight wow become WOW!
gwlee, from an online thread entitled: Aperture Fever? 8″vs 10″ or 12″
I think 1 object where a 10″ shines over an 8 is breaking open the larger globulars. A 10 keeps up pretty well with a 12 on globulars, but a 12 is noticeably better on everything else(except maybe the moon). Glad you mentioned Jupiter and Saturn. People tend to think that more aperture is just for fainter stuff, but that extra resolving power is very noticeable on planets. My friends 12 always showed more detail on Jupiter than my 10. Even with my 16, seeing details like spiral arms in galaxies is tough – takes dark skies and good transparency along with averted vision/dark adapted eyes. It is possible in a 12 and even a 10 under great conditions.
spaceoddity, from an online thread entitled: Aperture Fever? 8″vs 10″ or 12″
There was a time I owned an 8 inch and a 12.5 inch. Then a 10 inch F/5 was offered on Astromart at a very good price and bought it .
I went from 8 to 12 and it’s a big, big difference. While I got a lot of use out of my 8″, the 12″ opened up a new world of high power planetary nebulae observing, and revealing more detail and structure in galaxies.
Crazypanda, from an online thread entitled: Aperture Fever? 8″ vs 10″ or 12″
Going from 8 to 12 is a good jump. My CFO reluctantly okayed my purchase of a 12 inch dob (I had an 8 inch). She likes globs. After seeing M13 (and other globs) in the 12 inch, she said it was a good purchase!
jnmastro (Minnesota, USA), from an online thread entitled; Aperture Fever? 8″ vs 10″ or 12″
If you are looking for a dramatic improvement on most but not all objects that would be visible in both, get the 12-inch. Yes you can see a difference in the views between an 8 and a 10-inch, and yet again between a 10 and a 12-inch. It won’t be dramatic however, but the difference between an 8 and a 12-inch is much greater. You’ll get more than twice as much light gathering power, and that will improve the views of many objects you can see through an 8-inch, and show others that won’t be seen through an 8-inch. However, if you are going to transport it in a car, the truss-tube or collapsible Dob is the option you want. If you have a bigger vehicle, or do not need to transport it to use it under at least reasonably dark skies, a solid tube Dob might be a better, and a less expensive option too.
Achernar(Alabama, USA), from an online thread entitled: Aperture Fever? 8″ vs 10″ or 12″
Good luck with your new 12 when you get it. FWIW, I have an 8, 10 and 12.5 (plus 6, 4.5 and 66mm). The 10 gets used the most by far. While I did build all 3 to be lightweight, the 10 inch f/6.3 sits a few feet from the patio door and gets carried out most clear nights when the moon is not involved. You could always get a ten in the future too, after you have used the 8 and 12 for a while. The 10 never fails to pIease, although the 12.5 will always do a little better side by side. The 12.5 is f/5.9 and is a bit much to carry out fully assembled, so using it means taking the time to put it together, although that only takes a few minutes. Actually, I hope to keep them all for a long time…
Don H(SW Desert, USA), from an online thread entitled: Aperture Fever? 8″ vs 10″ or 12″
But no matter how you cut it, a good old school 8″ F/8 Newt is the best scope going. Just the 1.5″ shaft mounts from all the makers were just total garbage in my book. Slap that 8″ F/8 on a AP 1200 and you are as good as gold.
CHASLX200( Tampa, Florida, USA), from an online thread entitled: Long Slow Newtonians
I have the SkyWatcher 6.( f/8)…….It’s my favorite scope, and I just spent nearly a thousand bucks on a 110mm ED refactor I use less often ……….This baby’s a keeper. It has ease of use and portability written all over it, and although I can see coma in it, it’s really negligible at F/8. I see all kinds of coma in my 8” F/6, but it’s just not a big deal at F/8. The F/8 parabola throws up one nice image, and that’s a fact!
ColinOfAlabma(Texas, USA), from an online thread entitled; Long Slow Newtonians
I have an 8” F9 truss on a dob mount, and I have no problem tracking. I had a 10” F5.6 Discovery dob that put up great images, but in comparison to the 8”, it just couldn’t compete at high powers, so I sold it. For me, a GEM isn’t something that would be worth the trouble.
Galicapernistein, from an online thread entitled; Long Slow Newtonians
Yes, if planetary performance is the ultimate application of the telescope, 99.9% of CN members would not have enough money to buy an Apo that could beat a 10″ f/6 with high quality mirrors.
What difference is the theory of the argument if you can’t actually be realized in practical application?
My mass produced 12″ Newtonian has given me the best planetary views I have had in 30 years of observing and I have owned 6″ Astro-Physics and C14. Now the mirrors on my sample came out of the box with a level of quality I was surprised to see, so I would not say the everyone would be fortunate enough to share this experience.
I have owned 5″ Apo and while it is very sharp and contrasty, at very high powers, the types you can use on nights of superb seeing, the view gets far too dim. The colors lose saturation, and the image gets grainy due to the very small exit pupil. People dismiss the role of luminance on the observer’s ability to resolve low contrast detail and to me, that is unfortunate. The larger aperture produces a much brighter image (for a given power) and stimulates more cones in the observer’s eye, and this is the real key to seeing low contrast planetary detail. You have to fire as many cones as possible.
Eddgie, from an online thread entitled: 5″ Apo versus Best 7″ MAK CASS
Focal length does not really matter for planetary. Have an Antares 8 inch f5 with refigured mirror to 1\14 wave that beats the heck out of my old 8 inch f7 claimed 1\8 wave Optical Mechanics scope. Quality of the main mirror is everything.
When Mars came by spring 2014 the 8 inch f5 was showing the exact same views as my recently acquired APM 6 inch f8 double. Did not keep the APM very long.
Starlease(Rocky Mountains, USA), from an online thread entitled;Long Slow Newtonians
CHASLX200, on 08 Feb 2019 – 11:18 AM, said:
True. My best planet views came with F/5 or faster Zambuto and OMI optics in the 11 to 18″ range.
And that’s my experience, too — that a well made newtonian will beat anyone’s refractor 2″ or less of aperture. Heck, I had the same experience with far from “prime” optics. About 13-odd years ago, a friend of mine, God rest his soul, had one of the original Orion 120mm ED scopes, the one that came with the single-speed Synta Crayford, and its image of Saturn simply couldn’t keep up with my Meade LightBridge 8″ dob (GSO). So 4.7″ of unobstructed Chinese doublet lens couldn’t match the Taiwanese parabolic mirror’s 8″ optical capacity. People who claim otherwise, I guess the dob owners either had particularly bad mirrors (possible) or simply didn’t know how to collimate them (likely), or the mechanicals in their scopes can’t hold collimation well (as likely). I can’t explain refractor people with their APM’s and the like, when most reasonably well made 8″ dobs (and especially anything larger) will clean them up on the planets, or most anything else. We’ve got a guy in town with an XT10i that has an exceptionally good mirror, keeping up with custom scopes, and that thing shows the planets, not to mention DSO’s, better than anyone’s sub observatory sized refractor.
But it’s not just the figure of the mirror, it’s the mechanicals to maintain collimation, and the maintenance will and ability of the scope owner to keep and maintain his scope in top functioning order. Reflectors do require all three of these things, excellent optics, good mechanicals, and will and skill of the owner. Refractors only require good mounts – of course they require good lenses, too, but they seem to (mostly) come with pretty decent ones these days. It’s goes without saying that achromats have other issues, but with ED scopes, it’s usually true that they function quite close to their capacity. Given the three variables for reflectors, many out in the field are not up to par, giving people the impression of the superior refractor.
CollinofAlabama(Lubbock, Texas, USA), from an online thread entitled: Long Slow Newtonians.
ColinofAlabama makes some excellent points. A good Newtonian can perform as well or better than a refractor or any other type of telescope of the same aperture and since you normally get considerably more aperture with a Newtonian it is the optimal choice for a telescope. I have been using my Mikage 210 mm F/7.7 Newtonian since I purchased it in 1988 while stationed in Japan. Those of us who use Newtonians understand and accept that they require more effort than some other types of telescopes to keep them performing at their best. However, it pays of with excellent results whether it is being used for visual or astrophotography.
Stephen Kennedy(California, USA), from an online thread entitled, Long Slow Newtonians.
Even my mass market 12″ dob easily showed more on pretty much every target that would fit into the field than my 6″ Astro-Physics triplet would.
I will say that if seeing perfect double star splits is high on one’s list, it is difficult to beat a large refractor, and of course you can get a slightly larger true field, but this comes at a huge costs both in terms of money and effort.
Here is my 6″ on a mount that I would say is a good compliment to a 6″ triplet:
Yeah, if you want to have your 6″ Apo be as solid at high power as a 12″ dob, you gotta put it on a hefty mount. This mount could hold this scope reasonably still at 200x, but it was four trips out the door to get it into action.
By comparison, my 12″ dob is kept outside in the corner of my covered patio, and goes out in one trip and I can be observing in less than 90 seconds.
To the OP, I would say the 14″ is going to be far more competent on a far greater range of targets. I know this because my 12″ is far more competent on a wider range of targets than my 6″ triplet was.
Of course these days, I would rater use my Comet Catcher with my Mod 3 Night Vision eyepiece than most other scopes. Way easier to move around and WOW! the stuff I can see!!!
Eddgie, from an online thread entitled; Visual Only Triplet Apo vs 14″ Dobsonian.
Snip: Deep 13: By the forgoing logic, I should just stick with my 5″ f/12 refractor with D&G lenses. It’s a really nice DIY scope, but it’s aperture limited. I can really blow up Saturn, but it’s dim. I think 8″ (Newt) is just the right size.
With the seeing, weather and temperatures in Ohio I think a 6 or 7-inch refractor would be the scope of choice on 99-percent of nights. Of course, an apo is expensive and an F15 achromat is long and unwieldy. So for ergonomic and budgetary considerations, I think an 8-inch Newtonian “optimized” for planetary observation is an excellent choice. Just don’t sell that 5” D & G!
Bobhen, from an online thread entitled, Ideal planet scope
Sorry, but I think I will. The justification for the 8″ f/8 is that it will replace the 5″ and the C9.25. The 5″ rides on an EQ6 that I don’t really need for anything else. I’ll get rid of the SCT first, since I’ve never really liked it. I’ll still have a TV101 if I really want a refractor view.
Deep 13, from an online thread entitled, Ideal planet scope
I know many astro people who have bought and sold dozens of scope and I doubt any of them see themselves as affluent. And I have run into extremely wealthy amateurs, but one need not be affluent to enjoy the hobby. A few visits to star parties will allow anyone interested the chance to look through a wide variety of scopes. And there are so many scopes today that offer high performance at very reasonable prices. To me the 8” Newtonian is the best of that group. Years back I bought a Cave 8” f/8 Model B and it was simply excellent optically. Paid something like $900 for it complete with the original mount. In many ways I wish I had never sold it!
Itha, (Bend, Oregon, USA), from an online thread entited, Ideal planet scope
An F/6 or longer focal ratio mirror of 8 or 10-inches aperture can be made to a very high standard of optical quality, and that matters a lot more than the focal ratio. I have seen incredible views of the planets during steady seeing through Dobs with focal ratios as low as F/4, but most telescopes where I got those memorable views were of F/6 or longer focal ratios. As long as you have high quality optics that are properly mounted, correctly collimated, and you have good seeing, hours of enjoyable observing of the planets await you.
Acernar(Alabama, USA), from an online thread entitled Ideal planet scope
Well after much lively discussion, and with consultation with my finance minister (spouse)…I have decided that the ES 12″ truss Dobson is in my future. Will be looking on CN and other dealers for a deal and hope to have finances in place within a couple of months! My 8″ Sky-Watcher will be my quick set up scope and the ES 12 will be my detail scope when good stable weather prevails! Thanks for all the comments!
Good luck with your new 12 when you get it. FWIW, I have an 8, 10 and 12.5 (plus 6, 4.5 and 66mm). The 10 gets used the most by far. While I did build all 3 to be lightweight, the 10 inch f/6.3 sits a few feet from the patio door and gets carried out most clear nights when the moon is not involved. You could always get a ten in the future too, after you have used the 8 and 12 for a while. The 10 never fails to pIease, although the 12.5 will always do a little better side by side. The 12.5 is f/5.9 and is a bit much to carry out fully assembled, so using it means taking the time to put it together, although that only takes a few minutes. Actually, I hope to keep them all for a long time…
Don H(SW Desert, USA) from an online thread entitled, Aperture Fever?, 8″ vs 10″ or 12″
The Portaball is my all time favorite telescope. I love my refractors and the larger dobsonians that I have owned, but if I could have only one telescope the Portaball-8 would be it. I am a friend of the firm so-to-speak and have traveled with Dave Jukem to NEAF for several years displaying and evangelizing the benefits of a high quality sphere/ball telescope. I have owned every iteration of the 8″ version of the telescope.
Peleuba(Baltimore, Maryland, USA), from an online thread entitled, Portaball Users- Sing their Praises.
In the late 90s I read something about Portaball and asked for their brochure. At the time I was living in Long Beach, CA and for any chance at “dark skies” had to drive anywhere from two to four hours so the portability was a huge plus, as were the Zambuto optics. After a chat or two with Peter Smitka I ordered a 10″ Portaball and then waited for it to be built. From the moment I unpacked the scope and set it up for the first time I knew I had made a great decision. What a marvelous scope! My best ever view of Mars was through the 10″PB easily beating the 6″ refractor I had at the same time. I liked the scope so much I ordered a 12.5″ PB with a Roundtable tracking platform. Selling the 10″ was hard as it had been such a great scope, but the 12.5″ gave a bit better performance especially on globulars and deep sky. I still have the 12.5″ along with a Starmaster 18″, 5″ Takahashi FC-125, a unique Cave 12.75″ with Quartz primary, and TEC200ED. The PB holds its own against everything and bests them in terms of portability. Many years ago I had friends over to look at Saturn. At the time I had the 12.5″ PB, a Takahashi FS-152, a Cave 8″ F/8 and a couple of smaller APOs. One of my friends asked “If you could only have one telescope what would it be?” Without a seconds hesitation I said, “The Portaball!” That is still true today.
Itha(Bend, Oregon, USA), from an online thread entitled, Portaball Users- Sing their Praises.
In 1997, I made a mistake in purchasing a 20 inch Obsession classic–too much hassle in loading, setting up, and reloading in a vehicle. Peter Smitka’s concept–the largest possible telescope that was easily portable intrigued me. I sold my Obsession, and purchased a 12.5 inch Portaball. I have enjoyed it for more than 20 years. You can’t use DSC’s and you can run into balance issues with heavier eyepieces. I bought a Tom O Platform, which was designed specifically for my telescope. It worked great, but now I rarely use the Platform. Just find, and nudge to keep the object in view. The Portaball is fun, and easy to use. You can easily spin the telescope to place the eyepiece exactly where you want it. It is very easy to load and set up. I put the telescope on my front seat, secured with a seat belt. The accessories are then placed in empty spaces in the vehicle. The optics are excellent, and the 12.5 inch Portaball performs outstandingly on all objects. Planetary detail is sharp and detailed. Deep sky objects show up very well at dark sky sites. I had purchased an 18 inch Ultra Compact. My Portaball gave better planetary views than the UC, however the UC had twice the light gathering capacity and sucked in the deep sky objects much better. I don’t know of Mag 1 still exists and makes the excellent Portaball. If I were buying a new telescope, I don’t know if I wouldn’t buy a different model. However, I do not plan to buy a new telescope, and I believe my 12.5 inch, F5 Portaball is my last, and my ‘forever’ telescope.
Gene T( South Texas, USA); from an online thread entitled, Portaball users- Sing their Praises.
Last night we FINALLY had a nice clear night! I decided to use my daughter’s XT6. I did a quick collimation using an Orion Laser collimator deluxe (my Astrosystems barlowed laser is 2” and the XT6 has a 1.25” focuser) and double checked with a Cheshire, it was close enough. I put the scope on the porch during dinner so it cooled down for like 1.5hrs.
First object we looked at was the moon. It was marvelous, razor sharp. I put in my ES 6.7mm 82 def eyepiece with an Orion Shorty Barlow (I have no idea where the heck I put my powermate!) and the view was still sharp at 358x. The dob motions were ok, a little jerky at this power (but better than my DSVM Mount). I didn’t miss tracking, I was fine with manually tracking. I literally stayed on the moon for an hour.
Next was Orion, at 179x, the trapezium E and F stars were plainly visible (no averted vision needed), the stars we pin pricks! So much detail in the nebula. I also was checking out Meissa A and B (cute double). I also tried to see Sirius B, it was hard since there was a diffraction spike right where it was, I though I got a few glimpses (I kept at it for 30min). Rigel was cool too. I also checked it the cluster in the Rosette Nebula (looks good in my ES 68deg 24mm eyepiece) and Pleiades.
These views rivaled the sharpness of my 120mm ED scope and easily is sharper than my 8inch Edge (I never get a chance to use that scope cooled down). I also discovered that I prefer the use a manual dob while sitting, no motor drives to fuss with, completely silent, much more intimate experience with the sky (my wife keeps saying it’s because I’m getting old). We use the Nexstar Evolution for outreach or when family is over, but by myself, I just want to take my time and get lost in space. I’m thinking a manual 12 inch dob (maybe 16 but 12 looks manageable) may be next on the wish list.
Alien Ratdog (Ann Arbor, USA); from an online thread entitled, Ode to the XT6
The only real answer to the 6″ F/8 regarding refractors is TFOV. Well, AP, of course, but I’m talking only visual. For visual astronomy, outside of a larger true field of view, refractors have so little over the 6″ F/8, it makes them hard to swallow. Now falling temperatures through the night can bedevil cooling for any mirror, making it nigh impossible to reach equilibrium, but that doesn’t happen commonly. Folks, I own four refractors, so I love them, too, but it’s always difficult to find a reason NOT to take out the 6″ F/8 vs any of my refractors. They’re simply the unsung hero of visual astronomy. If more refractor people owned them, they’d realize what Abe, the poor post-doc, has revealed to you, the telescope using public, this very March 12th, 2019. Hear ye, hear ye!
ColinofAlabama(Lubbock, Texas, USA), Ode to the XT6.
As a refractor weenie I must chime in. I’ve had an XT6 since 1997. Mine is a Guan Sheng scope with 19% CO, but performance sounds similar to yours. My TV85 and friend’s Tak 78 are really good small refractors and super sharp….but they lose/lost to the XT6 each and every night for astronomical targets. My friend with the Tak was so impressed with the performance of the Dob that he brought over his Tak FS102. Well, that lost too. So he brought it back several times and the result was always the same. I mean it was fairly close, a premium 4” APO is a nice scope, but fine lunar and planetary detail was easier in the 6”. And deep sky was not as close as lunar planetary. With a 7 Nagler at 171x in the Newt on M13, the eyepiece is literally filled with stars. His 102 showed 40 -60 at similar power, which surely ain’t bad, but the difference is apparent. And the Newt cost me 300 bucks! I got my TV85 a few years after the Newt…not because I thought the 85 would beat it..I knew it wouldn’t. And besides, Al Nagler told me it wouldn’t beat it the very first time I talked to him on the phone about scopes. I got the 85 for it’s versatility as a travel, solar, nature and astronomy scope. But as I’ve said for years, as a purely astronomical platform, a good 6” f/8 Dob is the best bang for the buck going. 300 bucks!
Alnitak 22, from an online thread entitled, Ode to the XT6
I had a 6″ f/8 for over ten years. Never realized how good I had it until I sold it.
Ed D (South Florida, USA), from an online thread entitled, Ode to the XT6
Can’t speak to the weight of the SW6 compared to the Orion XT8, but I own a GSO Zhumell 8″, and it’s a LOT heavier than the SW6. I absolutely love my Crayford dual speed, almost as much as I hated the 2″ r&p it came with. Sold it on CN Classifieds very quickly, however. I DID have to drill two small holes in the tube. The GSO dual speed Crayford’s four holes are a little farther apart left-to-right, but way too long top-to-bottom. I drilled two small holes just below the two bottom holes, and forced the screw through for the top two, which are tight but can be made to work without further drilling. I only put a plastic baggie over my secondary! But I removed my primary and then used a portivac to suck up all the metal shavings. The existing hole is more than enough for the dual speed Crayford focuser to go through, if you need that kind of infocus for a particular eyepiece. After I installed the GSO dual speed I put flocking opposite the focuser and around the primary area. I also checked the center spot (dead on, or dead on enough, awful close, and not enough off that I could easily detect it, but I used rulers and my eye, not an inferometer or anything scientific). I blackened the edges with a sharpie and measured the reflective diameter — 147.5mm for my SW6, so, really a 5.8″ objective, but close enough. Gives me a very forgiving F/R of 8.14. The SuperView 42mm provides a relatively comfortable 2º FOV, is under $75 shipped, and provides a nice 5.16mm exit pupil. That’s $420 for scope and 2″ dual speed Crayford upgrade, not bad. I ordered a $25 Orion 1 lb counterweight, cause I needed it, but again, even after flocking, you’re gonna have trouble spending more than $500 for this setup, and it’ll kick refractor derrière, pardonne-moi. And you can’t even get a 120mm achromat for this price, and even if you got one used for this price (which isn’t fair since these could be picked up used, too, of course) the mount and setup will always be about 3 times the hassle, not to mention what will happen to both scopes in any kind of wind. Dobsonians have it all over every other design in terms of wind. And I know. I live in West Texas.
The 6″ dob is da bomb for relatively light weight, easy to use, power-packed astronomy — easy to collimate and maintain with excellent results at the eyepiece. They’re winners, and the 2″ Crayford focuser is icing on the cake for me. There is no better value in astronomy, and at F/8, you really don’t have to worry about a coma corrector. Although the entire field in NOT coma-free, it’s close enough, and noticeably better than F/6. Refractors can still produce those oh-my-god 2.5º-plus fields that aren’t possible in a 6″ F/8, but the moon? Jupiter? Most DSOs which are smaller than 2º? Refractors that can beat the very portable 6″ F/8 are mostly found in observatories.
ColinofAlabama(Lubbock, Texas, USA), from an online thread entitled; Ode to the XT6.
As for the ideal planetary scope, the 3 best ones I owned were a Discovery F/9 dob, the Orion 7″ Mak-Cass, and the 6″ F8 Dob. I no longer have the Discovery Dob or the 7 ” Mak but I will never part with my 6″ f/8 dob. It’s very portable, with a quick cool-down time, it’s easy to collimate and it provides sharp lunar/planetary views. I simply plunk it down in my back yard and it’s ready to go.
Burgher, from an online thread entitled, Ideal planet scope
I have noticed that on the Moon and Jupiter both the contrast and resolving power is actually quite good
That’s what you really want right there. My 10″ is an Orion but they’re equivalent in their potential for quality mirrors. I had mine tested some years ago by John Hall and he told me he could probably make the numbers better on a test report by refiguring the primary but I’d likely never see any difference. I believed him. I put a bit of $ into a new top end including 1/16th wave Astrosystems (Antares) secondary and that made an easily seen optical improvement. That scope repeatedly puts up better images than considerably larger aperture SCT’s at outreach events and star parties. A friend of mine put a Zambuto mirror in his XT12g and then replaced the secondary with an Antares. He said the optical impact of the secondary swap was far greater, not per dollar spent but in absolute terms. I’ve made many improvements to that scope but it still has the original primary. I expect to keep it around ’til the end and it will have the same primary. You can likely find someone to refigure your mirror and take your cash but if it ain’t broke…
Havasman(Dallas, Texas, USA), from an online thread entitled, Testing SkyWatcher 10-inch Doby Primary Mirror.
Always, always, always, get the largest aperture you can that won’t break your bank account or your back. Aperture fever isn’t just a state of mind. It matters. Just ask the folks at the European Southern Observatory (ESO), who are shelling out over a billion dollars for the new 39 meter Extremely Large Telescope (ELT). It will be the world’s largest optical scope when it sees first light in 2024. Why are they building a 39 meter scope? Because the 100 meter scope they wanted, the Overwhelmingly Large Telescope (OWL), isn’t entirely feasible yet. Yet.
Why do I have a 12″? Because a 22″ or 24″ isn’t entirely feasible yet. Yet.
HDavid(Pine Mountain, Georgia, USA), from an online thread entitled: Aperture Fever?, 8″ vs 10″ or 12″
Meet the latest addition to our telescope family! My OneSky arrived yesterday and I had it out under the stars as soon as it got dark. I found the built quality and optics to be excellent and the telescope is an absolute joy to use. It came almost fully assembled and took just a few minutes to complete. The collimation was pretty close out of the box and I only had to make a few minor adjustments to get it spot-on. I haven’t tried the eyepieces that it came with opting instead to use my trusty 20mm Meade RG wide field eyepiece for first-light (33x , 2 degree FOV). The moon looked fantastic showing a generous amount of detail complete with Earthshine. The Pleiades were beautiful and fit nicely within the field of view. I then swung over to Orion sweeping from Orion’s Belt down along the Sword to the Great Nebula. The Nebula showed a nice expanse and level of detail. All four members of the Trapezium were nicely split as were the 6 members of Sigma Orionis. I then swept over to Sirius and star-hopped southwards to M41 and then up the eastern side of Canis Major back up to Sirius. I then star-hopped eastwards over to M47 and 46, and continued northeast to M48. I ended my brief first light by swinging over to Mizar and Alcor, and Mizar was easily split.
I usually star-hop using a 50mm finder, but the wide field of view of the OneSky with this particular eyepiece was sufficient to make star-hopping easy and comfortable. The motion of the OneSky was smooth and firm and it was very comfortable to move with my hands placed on the front ring and rear mirror cell. The OneSky fit very nicely on top of my standard Meade field tripod with the Peterson accessory tray as shown here. This work well while standing, but I may build a shorter tripod or table to make the telescope a little more comfortable to use while seated.
One small note on the focuser; the OneSky uses a simple threaded helical focuser that can get a bit wobbly as it is screwed out. Some apply a layer of Teflon tape or a thick grease to help take of the slack in the threads. I was planning on using a thin layer of grease on mine; however I found a simple alternative that worked well with this eyepiece. Briefly, I screwed the focuser almost all the way in where the motion is tight and firm and then set the rough focus by moving the eyepiece, locking it in place with the set screws, and then set the fine focus by turning the helical focuser just a tad. This made for a very solid focuser that was easy to adjust.
I am planning on making a few simple mods including blacking the edge of the secondary and making a simple shroud to help control dew and frost, but I am delighted with the scope just as it is. This is going to make a fantastic star-hopping companion to my imaging gear.
jgraham( Miami Valley, USA), from an online thread entitled; One Sky Newtonian, Astronomers without Borders
Glad to hear your SW 10″ dob has a good primary mirror. I’ve been very impressed with them. Not so with their secondaries, though. If you know someone with a good reference flat, have them test it. All 5 of the GSO and SW 2ndaries I’ve tested have been about 1/4 wave or worse. Even the cheapest Antares would be a good upgrade.
Precaud(New Mexico, USA), from an online thread entitled, Testing SkyWatcher 10-inch Doby Primary Mirror.
Getting a 10” Sky-Watcher collapsible dob was one of the best moves I ever made. When I want to take pictures of the moon for friends and family it’s what I use. I feel the optics in mine should be quite good( never looking through any others) but to say that it’s been exceptional to view through last winter and fall would be an understatement. And the views now with a CC are even more magnificent. I have not nor will probably ever have optics checked though. But would probably change the secondary down the road based of more experienced dob observers conclusions.
jond 105 (Detroit, USA), from an online thread entitled, Testing SkyWatcher 10-inch Doby Primary Mirror.
For visual observing, focal ratio isn’t really all that important. A high-quality 300-mm f/4 Newtonian will deliver dazzling planetary views — far better than a 90-mm f/13.3 Mak-Cas, which has both slightly longer focal length and much longer focal ratio.
Tony Flanders(Cambridge, MA, USA), from an online thread entitled, If a slow scope is for planets…
As far as planetary viewing, it’s generally limited by the seeing. Under a stable atmosphere, it’s limited by the aperture and the optical quality. When the seeing is stable, larger reflectors provide the best planetary views, refractors are just not big enough.
Jon Isaac(San Diego, California, USA), from an online thread entitled, If a slow scope is for planets…
nyx, on 25 Mar 2019 – 09:53 AM, said:
1) a 150/750 (f/5 – fast) or 2) a 150/1200 (f/8 – slower)
So, which of the two scopes is suitable for DSOs (visual only) and why?
It’s all a matter of opinion. In my opinion, both are suitable for visual, DSO use.
My preference would be for the 6-inch f/8 — smaller obstruction, less serious coma, less sensitive collimation, less expensive eyepieces will perform well with it.
But since you have the f/5, use it and enjoy it. It’s a very capable visual, DSO telescope in it’s own right. With the right eyepiece, you can achieve a wider true FOV than you could with the f/8 — potentially more pleasing views of the Pleiades, M31-32-110, and other large objects.
No telescope is ideal for everything!
Sketcher, from an online thread entitled, If a slow scope is for planets…
Your first telescope is never the wrong scope! Truth be told, all decent telescopes can be used for any kind of visual observing. Some may be tweaked a smidge toward one goal or another, but those differences are pretty small. In any case, the telescope’s optical and mechanical quality are far more important than the f/ratio or the size of the secondary mirror.
Personally, I find f/5 to be the ideal focal ratio for deep-sky observing with a Newtonian, all other things being equal. Coma is visible but very modest, and it’s easy to achieve a 7-mm exit pupil with widely available eyepieces.
In fact, I think that a 150-mm f/5 Newtonian with a 2-inch focuser hits a very particular sweet spot, achieving the best deep-sky views possible within its portability class. I am considering purchasing one to replace my current 130-mm f/5 Newtonian.
I would prefer a 150-mm f/5 to a 150-mm f/8 on optical grounds alone, and the fact that the tube is much shorter is a significant side-benefit. But mind you, if somebody gave me a high-quality 150-mm f/8 Newtonian, I would be thrilled, and I would use it very happily for deep-sky observing as well as planetary observing.
I would prefer a somewhat smaller secondary mirror. But the difference between a 63-mm secondary mirror and, say, a 45-mm secondary mirror is pretty subtle.
In very large apertures, Newtonian owners almost always prefer faster focal ratios simply to keep the instrument more compact, and to allow them to look through the eyepiece without using a ladder.
Tony Flanders(Cambridge, MA, USA), from an online thread entitled; If a slow scope is for planets…
Finally had some steady skies, so I tested my new XT8 on some doubles in Orion. Clearly viewed all 6 stars in the trapezium. Nice view of 4 members of Sigma.
Alnitak, Rigel, and Eta were easy and clear beautiful splits. Pretty happy with the XT8’s performance.
Bonco2(Florida, USA), from an online thread entitled, XT8 test night
Good choice, after 3.x years I still think my 8″ Newtonian delivers an impressive amount of things to look at. XT8, not too expensive, not too heavy, not to long and bulky.
The beginning of a nice journey for you.
N3p, from an online thread entitled, XT8 test night
I sold my Z10 and bought the XT8, thus I’ve been doing several tests. So far its met my expectations and is so much easier to transport. I must say tho the Z10 had equally good optics. It was just too heavy for me.
Bonco2( Florida, USA), from an online thread entitled, XT8 test night
Quid est veritas?
My astronomical world changed forever when I first took a modern SkyWatcher 8″ f/6 Newtonian for a serious spin under a dark sky. It was far less expensive than any of the other telescopes I had personally owned, including some fine refractors and Maksutovs, and it outclassed them all on every type of celestial target. It was the sweetest of revelations! Modest and marvellous in equal measure, Newtonians are my instruments of choice, based solely on visual performance, when I want to pursue either serious or casual observing.
Justice, truth, fairness.
Neil English is author of Chronicling the Golden Age of Astronomy
The Reviews and Comments on my latest work are now coming in:
To Be Continued……………………….
Astronomy With an Opera Glass (1888) by Garrett P. Serviss
Brief biographical outline: Garrett Putnam Serviss was born on March 24 1851 in Sharon Springs, New York, and educated at Johnstone Academy, New York. After finishing high school, Serviss entered the newly established Cornell University in 1868, graduating with a B.S. degree in Science with honours in 1872. During his time at Cornell, Garrett’s flare for the written and spoken word flourished, so much so that he won awards for poetry. After graduating, Serviss enrolled at Columbia College Law School and in June 1874, received his LL.B and shortly thereafter was admitted to the New York State bar. But practicing jurisprudence as a profession proved to have little appeal to the young man, so he tried his hand at journalism, accepting a job as a reporter and correspondent for the New York Tribune, which he pursued for two years. In 1876, he secured a job at The Sun ( not to be confused with the filth-filled modern newspaper bearing the same name!), becoming copy editor of the paper after just a few years of service. It was during his time at The Sun that Serviss began writing popularised science articles and in particular, a string of articles on amateur astronomy. Indeed, he was so successful in his popuular science writings that his employers created a special role for Serviss as ‘Night Editor,’ a post he maintained for ten years, from 1882 through 1892.
Like so many astronomy enthusiasts, Serviss’ interest in the celestial realm began in childhood on his parent’s’ rural farmstead, where his young eyes would have beheld the preternatural beauty of the night sky, arching from horizon to horizon. As his notoriety grew, Serviss was sought out by a growing fan base, who invited him to give public lectures in astronomy aimed at a lay audience. This allowed him to travel the length and breadth of the country and even on trips abroad to evangelise his love of the night sky. His great success as a science communicator led him naturally to a career as a professional writer, turning out a string of magazine articles and books; both fictional and non fictional, including A Trip to the Moon, Pleasures of the Telescope, and Astronomy in a Nutshell. Arguably his greatest and most far-reaching work in amateur astronomy was his Astronomy with an Opera Glass, which was first published in 1888, the subject matter of this blog.
Serviss was, through and through, a man of the great outdoors, enjoying hill walking and mountain climbing well into his autumn years. One of his greatest personal acheivements was to reach the summit of the Matterhorn in the Swiss Alps, which he accomplished aged 43 years. “It was done,” he said, “in an effort to get as far away from terrestrial gravity as possible.”
Among his other creations is a “Star and Planet Finder:” a forerunner to the modern planisphere, which he marketed in collaboration with a one Mr. Leon Barritt, which proved to be an indispensable science tool for school children throughout the United States. Serviss married Miss Eleanore Belts and together they had a son, Garrett P. Jnr., who excelled at athletics, winning the silver medal for his country in the High Jump at the 1904 Olympic Games in St. Louis. Sadly, Eleanore died in 1906, and just two days before Christmas 1907, his son also died whilst attending Cornell University.
In later life, Serviss re-married a Madame Henriette Gros Gatier, who hailed from Cote d’Or, France, raisng her two children to adulthood. The recipient of many literary and scientific honours, Serviss was well travelled and comfortably well off for much of his long life. He died aged 78 years, survived by his second wife, stepdaughter and stepson.
Overview of the Book: Astronomy with Opera Glasses: A popular Introduction to the Study of the Starry Heavens With the Simplest of Optical Instruments, was originally published in 1888 by D. Appleton & Company, London. This author will be making use of a high-quality modern re-print by Forgotten Books. The interested reader can also access an online version of the manuscript which can be perused here.
The book consists of a short introduction, followed by five chapters covering the four seasons, as well as a chapter dedicated to the Moon and the planets. It is a short book in the scheme of things, with just 154 pages.
Stargazing was never more popular than it is now. In every civilized country many excellent telescopes are owned and used, often to very good purpose, by persons who are not practical astronomers, but who wish to see for themselves the marvels of the sky, and who occasionally stumble upon something that is new even to professional star-gazers. Yet, notwithstanding this activity in the cultivation of astronomical studies, it is probably safe to assert that hardly one person in a hundred knows the chief stars by name, or can even recognize the principal constellations, much less distinguish the planets from the fixed stars.And of course of the intellectual pleasure that accompanies a knowledge of the stars.
Author’s comments: To me, the written and spoken word of the English language reached its zenith at the end of the 19th century, during what we might call today the Late Victorian era. Back then, morals were clear, unambiguous and understood by all and sundry. Men were men and women could be women. Granted, life was considerably harder than it is today, but it was also more purposeful with it. People had a clear idea of what their roles were in an ordered and harmonious society; a society that cherished self sufficiency and honest work. Garrett Serviss, in his elegant writings from this long forgotten era in human history, provides us with a glimpse of what the glory of the heavens meant to a man of letters. But like so many men of his ilk, Serviss can trace his earliest days to humble beginnings on a rural farmstead run by his family. The stars were a comfort to those agrarian people, who still looked to them as signposts or timepieces, marking the passage of the seasons; auguring the time of sowing, reaping and threshing.
Continuing the introduction, Serviss calls to mind the brilliant apparition of Venus in the early summer of 1887, when its great white light illumined the sky over Brooklyn Bridge. Many individuals, so Serviss informs us, thought it was the light from the Statue of Liberty. He continues;
And as Venus glowed in increasing splendor in the serene evenings of June, she continued to be mistaken for some petty artificial light, instead of the magnificent world that she was, sparkling ou there in the sunshine like a globe of burnished silver. Yet Venus as an evening star is not so rare a phenomenon that peple of intelligence should be surprised at it.
To Serviss, the general ignorance concerning our nearest planetary neighbour provides an excellent backdrop for what he considers to be an even deeper ignorance of the stars, “the brother of our great father, the Sun.” Serviss links this perceived indifference to the stars to the largely mathematical nature of professional astronomy which tended to intimidate those without a penchant for precision and calculation. Luckily, though Serviss was undoubtedly acquainted with some advanced technical learning, the methods in this work entirely dispense of any need for such erudition. The heavens have a natural beauty that appeals to the human mind, whose heart has a deep longing for eternity, as King Solomon of old so eloquently expressed in the Book of Ecclesiastes (3:11).
Serviss also has the presence of mind to allay fears that a sound knowledge of the heavens can only be achieved by possessing a large and expensive telescope:
Perhaps one reason why the average educated man or woman knows so little of the starry heavens is because it is popularly supposed that only the most powerful telescopes and costly instruments of the observatory are capable of dealing with them. No greater mistake could be made. It does not require an instrument of any kind, nor much labor…..
Author’s note: How refrseshing it is to read such words, living as we are in a world driven by the ugly sceptre of materialism. This author became aware of this as he spun his own elaborate web of materialism, acquiring ever more costly telescopes in the somewhat pretentious and utterly mistaken view that one must ‘pay to play’. Thankfully, he liberated himself from that deadly entanglement and now enjoys good but modest instruments in his pursuit of heavenly treasures.
Happy is he with his lot.
And with the aid of an opera-glass most interesting, gratifying, and, in some instances, scientifically valuable observations may be made in the heavens. I have more than once heard persons who knew nothing about the stars, and probably cared less, utter exclamations of surprise and delight when persuaded to look at certain parts of the sky with a good glass, and thereafter manifest an interest in astronomy of which they would formerly have believed themselves incapable.
It is at this juncture that Serviss begins to describe the simple optical accoutrement with which he weaves his inspiring allegory of the starry heavens; the opera-glass..
First a word about the instrument to be used. Galileo made his famous discoveries with what was, in principle of construction, simply an opera glass. The form of telescope was afterward abandoned because very high magnifying powers could not be employed with it, and the field of view was restricted. But, on account of its brilliant illumination of objects looked at, and its convenience of form, the opera glass is still a valuable and, in some respects, unrivalled instrument of observation.
Author’s note: By the time Serviss penned these words, the Galilean telescope was long relegated to a mere historical curiosity, owing to the introduction of the achromatic doublet which offered far superior performance in terms of correction of chromatic aberration, coma and astigmatism, and allowing far higher magnifying powers to be employed. Binoculars had ‘evolved’ * considerably too , even in the case of the humble opera glass as he describes in the next few paragraphs of the introduction.
*More a case of intelligent design than ‘blind evolution’ surely?
In choosing an opera-glass, see first that the object-glasses are achromatic, although this caution is hardly necessary, for all modern opera-glasses, worthy of the name, are made with achromatic objectives. But there are great differences in the quality of the work. If a glass shows a colored fringe around a bright object, reject it. Let the diameter of the object-glasses, which are the lenses in the end furthest from the eye, be not less than an inch and a half. The magnifying power should be at least three or four diameters.
Author’s note: A bona fide Galilean binocular would have consisted of a singlet convex objective and a singlet concave element as the eye lens. Yet, to a contemporary of Serviss, even at the extremely low powers delivered by such a device, chromatic aberration would be very objectionable and a very poor choice for the purposes of exploring the night sky.
Serviss continues by demonstrating to the reader a simple way to estimate the magnifying power of his/her opera-glass, by focusing on a brick wall and estimating “how many bricks seen by the naked eye are required to equal in thickness one brick seen through the glass.” This is fairly easily achieved by holding the opera-glass up to one eye whilst leaving the other free to image the unmagnified view. With a few second’s practice, one will be able to simultaneously image both the magnified and naked eye image, allowing one to make a good estimate of how much magnifying power the instrument is delivering.
The instrument used by the writer in making most of the observations for this book has object-glasses 1.6 inch in diameter , and magnifying power of about 3.6 times. See that the field of view given by the two barrels of the opera-glass coincide, or blend perfectly together. If one appears to partially overlap the other when looking at a distant object, the effect is very annoying. This fault arises from the barrels of the opera-glass being placed too far apart, so that their optical centers do not coincide with the centers of the observer’s eyes.
Author’s note: For those who are interested in the development of the binocular through history, this resource was found to be quite authoratative. There is also an excellent youtube presentation of early binoculars available for viewing here and its follow-up here.
Overview of the author’s instrument: While rummaging through an antique shop in the picturesque old English market town of Kendall, in the Lake District, Cumbria, the author’s wife spotted a curious leather case inside of which was found a dusty Galilean binocular. Prizing it out of the case, this author briefly tested it by focusing on a clock-face about fifty yards distant. The image was fairly dim, owing to the amount of dust on the lenses, but to his delight, the individual barrels were set just about at the optimal interpupillary distance to bring both eyes into a single, circular light cone. The focusing mechanism was found to be a bit stiff and clunky but still adequate for general use, and the lenses were pristine enough for him to take the decision to purchase the instrument and its brown leather case, all for the princely sum of £7.
What follows here is a series of photographs of the instrument for the interested reader.
The object glasses were measured to be 44mm in diameter, or 1.73 inches; which exceed Serviss’ minimum recommendations!
The instrument had a nice set of retractable lens shades. which could also double up as makeshift dew shields, which would ultimately come in handy during longer periods of field use.
The instrument has a “Made in France” inscription annexed to the left-hand barrel of the binocular but no manufacturer name was apparent. Curiously, the high-quality leather case accompanying the binocular is stamped “Made in England.” Somewhat puzzled, more inscriptions were found whilst racking the focus wheel outwards;
When the eye lenses were racked outwards using the central focusing mechanism, the inscription “War Office” was found on the left barrell whilst the right barrel had ” Model” but no further information could be discerned.
With this information, it became somewhat clear that these were World War I binoculars. Since France had a technological edge over Britain in the production of high-quality optical glass up to the beginning of the 20th century, it was reasonably assumed that there was a division of labour amongst these war-time allies, with the leather case being manufactured in England. Consulting an online forum dedicated to the Great War, confirmed the author’s suspicion of the division of labour adopted by Britain and France during World War I. Ascribing a date of manufacture corresponding to World War I was further substantiated by the uncoated lenses used in the instrument. Anti-reflection coating technology was still a few decades ahead when these binoculars were being made.
The instrument is constructed mostly of metal parts but the lens shades and the central focusing wheel look as though they were made of the earliest commercial synthetic polymer, Bakelite, which was used extensively after 1909. Source here.
The author then went about dismantling the binocular to clean the optical surfaces. Intriguingly, the instrument was very easy to take apart so that lenses could be cleaned before use;
After carefully cleaning the lenses and putting it all back together again, and tightening up the screw which adjusts the tension on the focusing wheel, the author was delighted by how much esier it was to use, with brighter and more crisp images to boot. The instrument was now ready for field use.
Preliminary testing of the instrument allowed this author to estimate its magnifying power at about 3.5x, just about the same as Serviss’ original instrument. Further tests on the night sky allowed him to estimate the field of view offered up by the instrument. Turning to the handle of the Ploughshare showed that the field glass was able to just about fit the stars Mizar and Alioth in the same field. Yet another test showed that the instrument was able to fit most of the main ‘V’ of the Hyades star cluster in Taurus, allowing him to estimate its field of view to be ~ 4.5 +/- 0.1 angular degrees; considerably less than a modern binocular but adequate enough to pursue this project.
There is no facility to adjust the interpupillary distance on this instrument or to adjust one ocular independently of the other, but this was not found to be an issue. Clearly, this was a no-frills instrument designed for basic use. There is no lavish overlaying of mother-of-pearl or some other ornate covering on this instrument like so many other beautiful Galilean binoculars dating from the late 19th century and early 20th century, but this is entirely in keeping with its intended use. And while it would be easy to get carried away, as it were, and imagine that the instrument was actually used on the battle front, this author was content with entertaining the idea that it might have only seen use by ordinary civilians.
In use, the ‘opera-glasses’ are not too lightweight. If they were, they would pick up the jitters from the author’s hand-holding all too easily but nor are they too heavy to render prolonged field use a chore. There is a lot to be said for field glasses that are ‘just right.’
The author was over the Moon with his purchase. This was a genuine example of an instrument described by Serviss, allowing this author to authenticate the literary descriptions proferred in the work. This is an important issue going forward; to really experience the visual sensations of a Victorian amateur, one ideally has to use an instrument from the same period, or as near as can be. There is little point in claiming that one has the heart of a Victorian observer without also using instruments that would have been right at home in the same period. Doing it any other way is little more than cheating lol!
Now we are ready to enjoy the night sky as Serviss may have viewed it through his simple opera-glasses. Since each chapter of the book can be enjoyed independently of the others, for convenience, this author will commence with an exploration of the autumnal (fall) night sky (Chapter III) since this is the season in which this blog was first initiated.
Chapter III The Stars of Autumn
Covering pages 60 through 88
It is certainly true that a contemplation of the unthinkable vastness of the universe, in the midst of which we dwell upon a speck illuminated by a spark, is calculated to make all terrestrial affairs appear contemptibly insignificant. We can not wonder that men for ages regarded the earth as the center, and the heavens with their lights as tributary to it, for to have thought otherwise, in those times, would have been to see things from the point of view of a superior intelligence. It has taken a vast amount of experience and knowledge to convince men of the parvitude of themselves and their belongings. So, in all ages, they have applied a terrestrial measure to the universe, and imagined they could behold human affairs reflected in the heavens and human interests setting the gods together by the ears. This is clearly shown in the story of the constellations.
Garrett Serviss, writing as he was at the end of the 19th century, held fairly typical ideas for his time regarding the plurality of worlds. He, like so many of his contemporaries, believed the vastness of the starry heaven pointed to humanity’s mediocrity (‘parvitude’) in the scheme of things. Although he does not explicitly express it, he probably believed life was commonplace in the Universe. Back then, scientists were totally ignorant of the sheer complexity of even the simplest living cell- equivalent to that observed in the largest of human cities – and so was not in a position to see the incredible unlikelihood of something as complex as a living thing coming into being without the mediation of an intelligent agency. Today, the consensus appears to be shifting considerably from this scientifically naive view of the ubiquity of life on other worlds, especially now since a great deal more scientific evidence has come to the fore strongly suggesting that life on Earth did not evolve in any Darwinian sense. As this author has explained elsewhere, Serviss’ view of humanity as “contemptibly insignificant” is demonstrably false. We are, almost certainly, the only sentient creatures ever to have been created aside from the angels (the host of heaven).
The tremendous truth that on a starry night we look, in every direction, into an almost endless vista of suns beyond suns and system upon systems, was too overwhelming for comprehension by the inventors of the constellations. So they assumed themselves, like imaginative children, as they were, by tracing the outlines of men and beasts formed by those pretty lights , the stars. They turned the starry heavens into a scroll filled with pictured stories of mythology. Four of the constellations with which we are going to deal in this chapter are particualrly interesting on this account. ….The four constellations to which I refer bear the names of Andromeda, Perseus, Cassiopeia and Cepheus, and are sometimes called, collectively, the Royal Family.
Author’s note: The constellations that Serviss has chosen to discuss at length are prominent in the skies of early autumn and are especially well placed at the latitude this author observes from:- 56 degrees north. Indeed, they are better placed in his skies than they were for Serviss, who presumably would have observed from mid-northern latitudes and afford a wealth of objects that can be studied with the opera-glass.
Maps 14 and 15, presented on page 62 and 64, respectively, highlight the main constellations visible at mid-northern latitudes throughout September and October. Only the far southerly constellations are out of reach of the author’s gaze. Before discussing the Royal Family, Serviss enters into a brief but fascinating discussion on the southerly constellation of Capricornus, the most diminutive constellation of the zodiac,with a particular mention to both Alpha and Beta Capricorni. He writes:
The stars Alpha, called Giedi, and Beta, called Dabih, will be recognized, and a keen eye will perceive that Alpha really consists of two stars. They are about six minutes of arc apart, and are of the third and the fourth magnitude, respectively.These stars, which to the naked eye appear almost blended into one, really have no physical connection to each other, and are slowly drifting apart.
Serviss then discusses the star Beta Capricorni.:
The star Beta, or dabih, is also a double star. The companion is of a beautiful blue colour, generally described as “sky blue.” Is is of the seventh magnitude , while the larger is of magnitude three and a half. The latter is golden yellow. The blue of the small star can be seen with either an opera- or field glass.
Author’s note: This author has always referred to Alpha Capricorni as ‘Algedi’, which in Arabic means ‘little kid.’ Serviss, on the other hand, chooses to use a variation of this appellation; ‘Giedi.’ Being very low in the skies of central Scotland, the duplicitous nature of this star is exceedingly difficult to discern with the naked eye, even on the steadiest of nights. Indeed, they are just about half the separation of Mizar & Alcor in the handle of the Ploughshare, for comparison. The opera-glass however, makes light work of showing two yellow suns, the brighter being +3.6 (Alpha-1) and the fainter +4.3 (Alpha-2). This is a wonderfully complex system for double- and mutiple- star enthusiasts located at more favourable latitudes further south, where each of these stars is found to be double in a small telescope. Alpha 1 & 2 are known as an optical double, as the stars are located at greatly different distances; 106 and 560 light years, respectively, and by chance alone are located along our line of sight
In the same field about 2.5 degrees further south, you will be able to make out the golden tint of third magnitude Dabih (Beta Capricorni). In modern 10 x 50s, it too is revealed to be a double star, the companion being of the sixth magnitude of glory. Alas, the low power of the opera-glass, as well as the large brightness differential between the two, not to mention its low elevation above the horizon, makes this very difficult, if well nigh impossible to discern. What can you make out?
On page 65, Serviss also mentions a curious thought entertained by Sir John Herschel regarding faint companions to bright stars:
A suggestion by Sir John Herschel, concerning one of these faint companions, that it shines by reflected light, adds to the interest, for if the suggestion is well founded the little star must, of course, be actually a planet, and granting that, then some of the other faint points of light seen there are probably planets too.
This is clearly an erroneous conclusion, as Serviss points out:
It must be said that the probabilities are against Herschel’s suggestion. The faint stars more likely shine by their own light.
This just goes to show that even great astronomers can be dead wrong! Having said that, it is possible to see Earth-sized objects at stellar distances. Take the famous ‘pup,’ the faint companion to the Dog Star, Sirius B, for example, which can be seen in a 3-inch telescope in the current epoch. The companion, a white dwarf star, is incredibly small and dense but highly luminous!
With the most powerful glass at your disposal, sweep from the star Zeta eastward a distance somewhat greater than that separating Alpha and Beta, and you will find a fifth-magnitude star beside a little nebulous spot. This is the cluster known as 30 M, one of those sun-swarms that overhwelm the mind of the contemplative observer with astonishment, and especially remarkable in this case for the apparent vacancy of the heavens immediately surrounding the cluster….
Author’s note: Throughout much of the 19th- and early 20th centuries, the Messier objects were denoted by a number followed by the capital letter, ‘M,’ in contrast to today, where the letter ‘M’ precedes the number. M30 (a bright, 7th magnitude globular cluster located some 26,000 light years away) can indeed be picked up as a distinctly non-stellar blob in an opera-glass but its full glory can only be appreciated with a modest sized telescope and high magnifications. The fifth magnitude star Serviss is likely referring to is 41 Capricorni.
Serviss then moves from Capricorn to Aquarius, situated to the northeast of the latter and more accessible to observers located at high northerly latitudes. Serviss launches into an interesting discussion of the mythology related to the celestial Water-Bearer, both in ancient cultures and in more recent Arabic lore.
The star Tau is double and presents a beautiful contrast of color, one star being white and the other reddish orange- two solar systems, it may be, apparently neighbors as seen from the earth, in one of which daylight is white and in the other red!
Tau Aquarii is indeed a beautiful and easy sight to behold in the opera-glass, with both stars being separated by about 0.65 angular degrees. Serviss’ fecund imagination goes to work here as he rightly considers the colour these stars cast on the landscape of hypothetical planets that might exist there.
Serviss then discusses the fascinating 8th magnitude object in Aquarius that we know today as the Saturn Nebula (NGC 7009), an appellation first bestowed upon it by the Third Earl of Rosse (Birr, Ireland).
Point a good glass upon the star marked Nu, and you will see, somewhat less than a degree and a half to the west of it, what appears to be a faint star of between the seventh and eighth magnitudes. You will have to look sharp to see it. It is with your mind’s eye that you must gaze, in order to perceive the wonder here hidden in the depths of space. The faint speck is the nebula, unrivalled for interest by many of the larger and more conspicuous objects of that kind. Lord Rosse’s great telescope has shown that in form it resembles the planet Saturn; in other words, that it consists apparently of a ball surrounded by a ring……..If Laplace’s nebular hypothesis, or any of the modifications, represents the process of formation of a solar system, then we may fairly conclude that such a process is now actually in operation in this nebula in Aquarius, where a vast ring of nebulous matter appears to have separated off from the spherical mass within it.
Author’s note: The visualisation of the Saturn Nebula with the opera glass is certainly possible but it only presents as a very faint 8th magnitude ‘field star’. Serviss, writing at the time when modern astrophysics was in its infancy, had no idea that what he was describing was not, in fact, a solar system in formation, but one rather that was in the process of dying. The Saturn Nebula is a prominent planetary nebula, a geriatric star in its final death throes, as it sheds its outer atmosphere to the great, cold dark of interstellar space.
On page 69, Serviss invites us to examine the star Delta Aquarii with the opera glass. At magnitude + 3.3, it shines with a blue-white hue. It is here, so Serviss informs us, that Tobias Mayer ” narrowly escaped making a discovery that would have anticipated that which a quarter century later made the name of Sir William Herschel world-renowned.” In 1756, the planet Uranus passed very close to this star but it moved so slowly that it escaped his notice.
Author’s note: The story of Uranus is really the story of ‘near misses.’ The historical archives reveal many such ‘nearly never made it’ sightings of the 7th planet orbiting the Sun. In fact, Galileo himself almost certainly sighted Uranus in the early 17th century, but did not realise its significance.
Above Aquarius you will find the the constellation of Pegasus. It is conspicuously marked by four stars of about the second magnitude, which shine at the corners of a large square, called the Great Square of Pegasus. This figure is some fiften degrees square, and at once attracts the eye, there being few stars visisble within the quadrilateral, and no large ones in the immediate neighborhood to distract attention from it
Author’s note: The Great Square of Pegasus is all the more remarkable for its great paucity of bright stars. Indeed, this is precisely the reason why it stands out so prominently in autumn skies. How many stars can you make out within the body of the square? From my reasonably dark site I can make out about, this author can make out maybe a half dozen stars ranging in magnitide from +4 to +5.5, most prominent of which are Upsilon, Tau, Psi and Phi, which vary in glory from +4.4 to +5.1. Additionally, when the constellation is higher up in the sky, and with good transparency and no Moon, additional members can be made out with some concentration; 71 Pegasi ( magniude +5.4) can be glimpsed near the centre of the square and 75 Pegasi (+5.5) just a few degrees further south. 85 Pegasi might also be glimpsed just above Algenib (Gamma Andromedae) near the border with Pisces. Many more are possible from the darkest skies, however. Indeed, counting the number of stars within the Great Square that are visible to the naked eye remains a good test of how dark and transparent your skies are. However, even a thin veneer of haze will all but extinguish the fainter stars visible to the naked eye on the best nights.
Although Pegasus presents a striking appearance to the unassisted eye on account of its great square, it contains little to attract the observer with an opera-glass. It will prove interesting to sweep with the glass carefully over the space within the square , which is comparitively barren to the naked eye but in which many small stars will be revealed, of whose exstence the naked-eye observer would be unaware. The star marked Pi is an interesting double, which can be separated by a good eye without artificial aid, and which, with an opera-glass, presents a fine appearance.
Sweeping with the opera-glass within the confines of the Great Square is still a worthwhile endeavour, where many fainter stars of magnitude 7 and 8 come into view. Though Serviss does mention it, the opera-glass is just the perfect optical accoutrement to properly discern the colour differences between the stars marking the vertices of the Great Square. To this author’s eye, only first magnitude stars clearly reveal their colours, but with the opera-glass you’ll be able to make out that Markab (Alpha Pegasi) and Algenib (Gamma) are lovely blue-white in hue, whilst Scheat (Beta) has, in comparison, a soft ruddy colour. Another beautiful target is Enif (Epsilon), located in the south-western edge of the Flying Horse, near the border with the diminutive constellations of Delphinus and Equuleus. Owing to its rather irregular variability, it can sometimes manifest as the brightest star in Pegasus, outshining all the others in glory, with its fetching orange complexion. Though a little beyond the low powers offered by the opera-glass, a larger field glass should also reveal Enif’s wide and faint (magnitude 8.6) companion.
It is somewhat surprising that Serviss fails to mention M 15, a bright, sixth magnitude globular cluster just off to the northwest of Enif. Appearing as a fuzzy star in the opera-glass, averted vision should allow you to see it swell to nearly twice the size it appears using direct vision.
Finally, another target worth seeking out is the fifth magnitude star, 51 Pegasi, a sun-like (G class) star located roughly midway between Alpha and Beta Pegasi. Situated just 50 light years from the solar system, 51 Pegasi was shown to have a planet about half the mass of Jupiter circling its parent star just a few million miles from its fiery surface. Fascinated as he was in the ‘plurality of worlds,’ were he alive today, Serviss would most certainly have waxed lyrical about this star system!
Serviss moves from Pegasus into Cetus, the Celestial Whale, and almost immediately launches into an interesting discussion on its most famous luminary; Mira (Omicron Ceti):
By far the most interesting object in Cetus is the star Mira. This is a famous variable- a sun that sometimes shines a thousand-fold more brilliantly than at others! It changes from the second magnitude to the ninth or tenth, its period from maximum to minimum being about eleven months. During about five months of that time it is completely invisible to the naked eye; then it begins to appear again, slowly increasing in brightness for some three months, until it sjines as a star of the second magnitude, being then as bright as, if not brighter than, the most brilliant stars in the constellation. It retains this brilliance for about two weeks, and then begins to fade again, and, within three months, once more disappears.
Author’s note: Mira is a wonderful subject for the opera glass. It was discovered to be variable by the Dutch astronomer, David Fabricius in 1596, barely a decade before the telescope first made its mark on European civilization. At its brightest, it is a handsome ruddy colour in the opera glass and, thanks to a number of suitable ‘reference stars’ of fixed brightness in its vicinity, which vary in glory from the 6th to the 8th magnitudes, they can be used to monitor its changing luminosity over the weeks and months.It’s period is 332 days.
Serviss explains that Mira is somewhat irregular in its maximum brightness though. For example, he informs us that in 1779 it shone with a brilliance more reminiscent of a first magnitude star. Acknowledging the Sun’s minor variability, Serviss supposes that the nature of its variability is attributed to much more prominent star spots (analogous to the sunpots on our own star) on its fiery surface:
Knowing that our Sun is a variable star-though variable only to a slight degree, its variability being due to the spots that appear upon its surface in a period of about eleven years- we possess some light that may be cast upon the mystery of Mira’s variations. It seems not improbable that, in the case of Mira, the surface of the star at the maximum of spottedness is covered to an enormously greater extent than occurs during our own sun-spot maxima, so that the light of the star, instead of being merelty dimmed to an almost imperceptibe extent , as with our sun, is almost blotted out.
Author’s note: Serviss was wrong in his explanation of Mira’s extraordinary variability. Its variability is actually caused by its sinusoidal expansion and contraction, from 400 to 500 times the diameter of our own Sun. It is this change in radius and temperature that gives rise to its variability. Mira is at the latest stage of its evolutionary journey and, as a result, is shedding its outer atmosphere to interstellar space.
Serviss wonders whether the antics of Mira might reflect the fate of our own star in the aeons to come:
We might even go so far as to say that possibly Mira presents to us an example of what our sun will be in the course of time, as the dead an barren moon shows us, as in a magician’s glass, the approaching fate of the earth. Fortunately, human life is a mere span in comparison with the aeons of cosmic existence, and so we need have no fear that either we or our descendants for thousands of generations shall have to play the tragic role of Cambell’s ” Last Man,” an endeavor to keep up a stout heart amid the crash of time by meanly boasting to the perishing sun, whose rays have nurtured us, that, though his proud race has ended, we have confident anticipations of immortality. I trust that when man makes his exit from this terrestrial stage, it will not be in the contemptible act of kicking a fallen benefactor.
Author’s note: Like human beings, stars are at their most unstable when very young and very old. In middle age, they enjoy much greater stability. Our Sun, now in its stable mid-life, is the least variable star known to astronomical science. Greater variability would be very dangerous for the life that teems on this planet. Is it a coincidence that humankind arose on the scene during this period of maximum solar stability? I think not. This is the best possible time to launch a global civilisation, where billions of human beings can enjoy the benefits of great scientific advances that make our lives comfortable. It was planned that way and can only last for a definite amount of time before things go downhill for one and all. The Biblical authors affirm that the Earth is not our ultimate home;
For here we do not have a lasting city, but we are seeking the city that is to come.
The text on autumn skies moves from Cetus into Pisces, a large and sprawling constellation snaking its way from ‘under’ the square of Pegasus (as seen from the northern hemisphere), northeastwards where it borders with Andromeda, the Chained Princess. Beginning with some mythology associated with the constellation, Serviss then suggests we sweep our opera glasses from northeast to southwest and examine the many delightful stars that fall into the field of view:
You will find it very interesting to take your glass and , beginning with the attractive little group in the Northern Fish, follow the windings of the ribbon, with its wealth of tiny stars, to the Western Fish. When you have arrived at that point, sweep well over the sky in that neighborhood, and particularly around and under the stars Iota, Theta, Lambda and Kappa. If you are using a powerful glass, you will be surprised and delighted by what you see.
Author’s note: The most distinctive feature of this constellaton is the attractive loop of seven stars situated at its southwestern edge known as the Circlet. The field of view offered up by the opera glass used by this author is not large enough to encompass them all, but a modern, wide-angle binocular can certainly do so. Centre Kappa and Lambda Piscium in the field. Just a short distance south of these stars lies the spot where the Sun crosses the celestial equator, heralding the arrival of Spring in the northern hemisphere. While you’re there, it’s worth checking out a pretty little asterism known as Alessi J23407+0757 situated just over two degrees north of Iota Piscium. Appearing quite smudgy in the opera glass owing to its small image scale, it makes a delightful telescopic sight consisting of about half a dozen stars.
Serviss leaves Pisces and then moves into Aries, the Ram, sandwiched between Taurus and Andromeda, where he invites us to explore its two brightest luminaries, set about four degrees apart; Alpha Arietis(Hamal) and Beta Arietis (Sheratan), both of the second magnitude. They present an interesting case of colour contrast, with Hamal shining with a soft orange hue while Sheratan is revealed as blue-white in the opera glass. On page 75, Serviss gives mention to Gamma Arietis(Mesarthim). He writes:
Gamma Arietis, is interesting as it was the first telescopic double star ever discovered. Its duplicity was detected by Dr. Hooke while watching the passage of a comet near the star in 1664.
Author’s note: The opera glass will pick up a faint star ( 7 Arietis) just west of Mesarthim, but this is not the duplicity Serviss speaks of. In a small telescope using low power, magnitude 3.9 Mesarthim is seen to be composed of two stars, both white and of nearly equal magnitude; 4.6 and 4.7.
At the bottom of page 75, Serviss returns to one of the themes he raises earlier in the chapter, by finally introducing the constellations that comprise the ‘Royal Family,’ consisting of Perseus, Andromeda and Cassiopeia, all featured on Map 17 on page 77 of the text. After discussing their interesting mythology, he finally begins the astronomical discussion of these constellations on page 79, where he notes the great riches to be found within their confines;
The starry riches of these constellations are well matched with their high mythological repute. Lying in and near the Milky-Way, they are particularly interesting to the observer with an opera glass. Besides, they include several of the most celebrated wonders of the firmament.
Serviss begins with Andromeda and its greatest attraction to the possessor of an opera glass; the Great Nebula (M 31):
In searching for picturesque objects in Andromeda, begin with Alpheratz and the groups forming the hands. Below the girdle will be seen a rather remarkable arrangement of small stars in the mounth of the Northern Fish. Now follow up the line of the girdle to the star Nu. If your glass has a pretty wide field, your eye will immediately catch the glimmer of the Great Nebula in Andromeda in the same field with the star.
Author’s note: The “Great Nebula” in Andromeda is indeed a fine sight in the author’s opera glass, where its central bulge and extended spiral arms look rather like two fried eggs set back to back.
He continues on page 80 to inform us that this deep sky object is the “oldest or earliest discovered of the nebulae, and with the exception of that in Orion, is the grandest visible in this hemisphere.”
An illustration of what the Andromeda Nebula looks like in an opera glass is provided on page 80, together with an early reference to averted vision:
By turning the eyes aside, the nebula can be seen, extended as a faint, whispy light, much elongated on either side of the brighter nucleus.
Author’s note: We have a tendency today to think that many of the more advanced skills employed by visual observers are essentially modern developments. And yet Serviss clearly reveals to us that the eminently useful activity of using averted vision (using the night-sensitive rod cells situated either side of the fovea) was known and used to good effect at the end of the 19th century.
On page 80 through 81, Serviss described the curious phenomenon of a nova seen superimposed on the Andromeda Nebula in 1885, which flared up suddenly and faded back to invisibility in the course of just a few months. He does not however, reveal the interesting story of its discovery.
Author’s note: What Serviss is almost certainly referring to is SN 1885, which was first chanced upon by the French astronomer; Ludovic Gully, on the evening of August 17 1885 from Rouen, France, during a public stargazing event. Intriguingly, Gully dismissed the event as an artifact of ineffective baffling of his telescope from scattered moonlight and so did not follow it up and report it to the broader astronomical community. Just two evenings later, it was apparently seen by the Irish amateur astronomer, Isaac Ward(1834-1916), based in Belfast, who described its appearance as ruddy and with an estimated magntude brightness of + 7.
SN 1885A was picked up by Ernst Hartwig, based at Dorpat (Tartu) Observatory, Estonia, on the evening of August 20 1885, when its existence was finally communicated to the international community. Despite attempts by both Gully and Ward to claim it as their own, the discovery of ‘S Andromedae’ (the common name soon bestowed upon it), was credited to Hartwig. SN 1885A was a supernova, which reached its maximum brightness of +5.85 on August 21 1885 after which it faded back to magnitude 14 a year later. More historical information regarding the object can be viewed here. SN 1885A retains the distinction of being the only supernova event to have been viewed in the Andromeda Galaxy to this day.
That Serviss was largely ignorant of the true nature of SN 1885A is no surprise. Astronomers knew very little in these early days considering how massive stars end their lives. What is more, we also gain a glimpse of how small the cosmos was thought to be at the end of the 19th century. Concerning the ‘nova’ in Andromeda he writes;
Although it appeared to be beside the bright nucleus of the nebula, it is likely that it was really hundreds or thousands of millions of miles either this side or the other side of it.
On page 81, Serviss encourages users of the opera glass to conduct sweeps through Andromeda eastwards towards Cassiopeia and Perseus. As we do so, the richness of star fields increases dramatically as our portal on the heavens rejoins the meandering river of stars that is the Miky Way. On page 82, Serviss pauses to consider Gamma Andromedae, which presents in a comely golden hue in the opera glass. He also points out that this is the spot in the sky that demarks the radiant of the Biela (Andromedid) meteor shower, so called after the astronomer who first discovered a short period comet that graced the inner solar during the mid 19th century.
Author’s note: Serviss was also a keen telescopist and indeed published a splendid book (mentioned earlier in passing) dedicated to the sights within reach of a small telescope. What’s more, this author imagines him using both the opera glass and the telescope profitably to bring the many treasures of the northern sky within reach of his eyes. Serviss alerts us to the beautiful colour contrast triple system, Gamma Andromedae (pp 82), which is a delightful sight in a telescope employing moderate powers. Before leaving Andromeda, be sure to check out the terrific binocular triple, Nu Andromedae. Observers with the keenest eyesight should try their hand at seeing this triple system with the naked eye.
Next let us turn to Perseus. The bending row of stars marking the center of this constellation is very striking and brilliant. The brightest star in the constellation is Alpha, or Algenib, in the center of the row. The head of Perseus is toward Cassiopeia, and in his left hand he grasps the head of Medusa, which hangs down in such a way that its principal star, or Algol, forms a right angle with Algenib and Almach in Andromeda.
Perseus, the classical Hero, presents some of the most spectacular sights to the user of an opera glass. The opulent splashing of stars around Alpha Persei (Algenib) is presented in the star map on page 84 of the text and cries out for exploration. After discussing the Demon Star, Algol, Serviss turns his attention to the region of sky around Algenib:
Turn now to the bright star Algenib, or Alpha Persei. You will find with the glass an exceedingly attractive spectacle there. In my note-book I find this entry, made while sweeping over Perseus for materials for this chapter: “The field about Alpha is one of the finest in the sky for an opera glass. Stars conspicuously ranged in curving lines and streams. A host follows Alpha from the east and south.” The picture on page 84 will give the reader some notion of the exceeding beauty of this field of stars, and of the singular manner in which they are grouped, as it were, behind their leader. A field glass increases the beauty of the scene.
Author’s note: The reader will note that Serviss refers to Alpha Persei as ‘Algenib’ rather than the more familiar name of ‘Mirfak’ used by astronomers today.
Serviss took notes while observing; an essential activity for any serious observer!
In October, Perseus rides very high in the sky at the author’s location, making it especially well placed for observation. The stream of stars around Mirfak referred to by Servis is known today as the Alpha Persei moving cluster (or association). Centring the opera glass on Mirfak reveals about a dozen stars of magnitue 6 or greater within a two degree radius anda few more ‘outliers’ can be picked up by virtue of the glass’ larger field of view (~4.5 degrees). This remarkable clustering of star light presents one of the most spectacular sights in all the northern heavens using a field glass. Indeed, so large and sprawling is this cluster that it is somewhat lost in the field of view offered up by even the smallest rich field ‘scope!
Modern binoculars have come an awful long way since Serviss penned his words. Today, one can obtain very decent binoculars for a modest price offering much higher contrast, magnification and field of view than anything Serviss could have dreamed of! The author’s 8 x 42 binocular, for example, samples a field fully 7.3 degrees wide, and with a higher magnification can pull out considerably fainter members than any early 20th century field glass. This instrument makes observing through the old field glass more like looking through a straw than anything else!
Isn’t modern technology wonderful!
This author considers it a great blessing that he is able to use such a wonderful optical instrument from the 21st century!
Observing the Alpha Persei Association with a modern binocular cannot fail to introduce a deep sense of awe concerning the vast beauty of the heavens!
The reader will find a starry cluster marked on Map 17 as the “Great Cluster.” This object can be easily detected by the naked eye, resembling a whisp of luminous cloud. It marks the hand in which Perseus clasps his diamond sword, and, with the aid of a telescope of medium power, it is one of the most marvelously beautiful objects in the sky- a double swarm of stars, bright enough to be clearly distinguished from one another, and yet so numerous as to dazzle the eye with their lively beams.
Serviss is referring to the famous Double Cluster (Caldwell 14) located about mid-way between Perseus and Cassiopeia. This is undoubtedly one of the crown jewels in all the heavens, and while it can be seen as a foggy whisp with the naked eye, any optical aid makes it look immesaurably better. Serviss writes;
An opera glass does not possess sufficient power ” to resolve” this cluster, but it gives a startling suggestion of its half-hidden magnificence….”
Author’s note: The view of the Double Cluster is considerably improved with an opera glass, but it is much better seen with decent aperture telescopes. This author observes it pretty much routinely for much of the year and finds that the view becomes better and better the larger the telescope is employed. There will be a natural limit though, as the largest telescopes will have a field of view that becomes too small to sample the full glory of this celebrated deep sky object. The best view he has had in recent years is through a 12″ f/5 Newtonian reflector using a 34mm wide angle eyepiece serving up a power of 45x in a 1.5 degree true field, but a very close second is at 59x in the same telescope in a one degree field.The latter is slightly less favoured, as it restricts some of the hinterland to these clusters from being comfortably observed.
Nearby, about mid-way between Algol and the lovely golden Gamma Andromedae (Almach), the opera glass makes light work of picking up the open cluster also mentioned by Serviss as’ 34 M’. When high in the sky, during October and November, one can make out perhaps a half dozen of its brightest stellar members and perhaps twice that with a 10 x 50 binocular. Telescopically, M 34 is reasonably rewarding, presenting a rich scattering of white, yellow and orange stars at moderate medium powers.
Serviss next invites us to explore the rich stellar archipelagos of Cassiopeia, easily made out as ‘wonky W’, as this author affectionately refers to it. Serviss writes:
Here the Milky-Way is so rich that the observer hardly needs any guidance, he is sure to stumble upon interesting sights for himself. The brightest stars are generally represented as indicating the outlines of the chair or throne in which the queen sits, the star Zeta being in her head. Look at Zeta with a good, field glass, and you will see a singular and brilliant array of stars near it in a broken half circle, which may suggest the notion of a crown.
From here, Serviss invites the reader to visit a locus very near the star Kappa Cassiopeiae, denoted by a very small circle on Map 17 ( page 76). A number is assigned to this locus:- 1572. Intriguinginly, this little spot makes Serviss’ mind races:
This shows the spot where the famous temporary star, which has of late been frequently referred to as the “Star Of Bethlehem,” appeared. It was seen in 1572 , and carefully observed by the famous astronomer Tycho Brahe. It seems to have suddenly burst forth with a brilliance that outshone every other star in the heavens, not excepting Sirius itself. But its supremacy was short-lived. In a few months it had sunk to the second magnitude. It continued to grow fainter, exhibiting some remarkable changes of color in the meantime, and in less than a year and half it disappeared.
Serviss goes on to say that in 1264 and 945 AD, similar outbursts of brightness were recorded at the same location in the heavens. Serviss seems to suggests that a legend grew up around this ‘nova’ and that it could also be the location of a star that burst forth during the time of the birth of Christ. Yet, Serviss exercises caution when entertaining such legends;
In short, there are two many suppositions and assumptions involved to allow any credence being given to the theory of the periodicity of Tycho’s wonderful star. At the same time, nobody can say it is impossible that the star should appear again, and so it may be interesting to the reader to know where to look for it.
Author’s note: Serviss is justified in expressing caution in attributing the Star of Bethlehem to Tycho’s Star. As a Bible believing Christian, the ‘Star’ was undoubtedly a real phenomenon, as were Christ’s teachings, miracles, death and resurrection. Best to leave it at that! No harm done in visiting this spot in Cepheus from time to time!
On page 88, Serviss brings his tour of the autumn sky to an end by briefly considering a couple of stars in Cepheus; particularly Herschel’s Garnet Star, Mu Cephei, the deep sanguine hues of which will delight the user of an opera glass, as well as the wonderful Delta Cephei, a celebrated double and variable star, the components of which are quite widely spaced. Serviss writes:
With a good eye, a steady hand and a clear glass, magnifying not less than six diameters, you can separate them, and catch the contrasted tints of their light.
Author’s note: The separation of Delta Cephei A & B has hardly changed since Serviss penned his words. Today they are separated by 41,” precisely the number proffered by Serviss at the end of the 19th century (see page 88). Try as he may, this author has not been able to prize the components apart using his low power opera glass. Even his steadily-held 8 x 42 failed the test. He has however found it no trouble to separate the components using a power of about 15x in a 80mm shorttube achromatic telescope on a steady night with good transparency. But one can easily monitor the changing brightness of the Cepheid variable (Delta Cephei A) with an opera glass, which gradually fades from magnitude 3.5 back to 4.4 over a period of about five days and 9 hours.
Chapter IV The Stars of Winter
Covering pages 89 through 117.
I have never beheld the first indications of the rising of Orion without a peculiar feeling of awakened expectation, like that of one who sees the curtain rise upon a drama of absorbing interest. And certainly the magnificent company of the winter constellations, of which Orion is the chief, make their entrance upon the scene in a manner that may be described as almsot dramatic. First in the east come the world-renowned Pleiades. About the same time Capella, one of the most beautiful of stars, is seen flashing above the north-eastern horizon. These are the sparkiling ushers to the coming spectacle. In an hour the fiery gleam of Aldebaran appears at the edge of the dome below the Pleiades, a star noticeable among a thousand for its color alone, besides being one of the brightest of the heavenly host. The observer familiar with the constellations knows, when he sees this red star which marks the eye of the angry bull, Taurus, that just behind the horizon stands Orion with starry shield and upraised club to meet the charge of his gigantic enemy. With Aldebaran rises the beautiful V-shaped group of the Hyades.
Despite being separated by over a century of time, Serviss’ opening lines in this chapter covering the winter sky, immediately resonate with this author, as though he were standing right beside him on a clear and dark winter evening. Orion is indeed the great herald of the hyemal heavens, its august form dominating the meridian from well after midnight in early December but arriving increasingly earlier as the winter progresses.
As well as hosting a riot of bright stars crying out for observation with an opera glass, Orion’s brilliant luminaries – Rigel and Betelgeuse – are accompanied by a host of brilliant suns that decorate the heavens: Sirius and Procyon dominate the sky low in the southeast, and higher up, fiery red Aldebaran in Taurus, and creamy yellow Capella, the jewel of Auriga. The heavenly twins, Castor & Pollux boldly announce the arrival of Gemini, and over in the west at sunset, the white and blue-white luminaries of summer still make their presence felt; Altair in Aqulia, Deneb in Cygnus and Vega corruscating wildly in the denser air at lower altitude.
This rich assortment of bright stars create the unmistakable impression that the winter sky is darker than at other times of the year. And, indeed, there is more than a grain of truth to this assertion; for it is at this time of year that our gaze begins to carry us away from the extremely bright centre of our galaxy, and faces the Perseus spiral arm of our Milky Way.
Of such an array of bright winter stars, Serviss believes it is unrivalled in all the heavens;
The heavens contain no other naked-eye view comparable with this great array, not even the glorious celestial region where the Southern Cross shines supreme, being equal to it in splendor.
From his observing site in the populous borough of Brooklyn, Serviss provides a historically interesting titbit regarding the encroach of light pollution in urban settings:
To comprehend the real glories of the celestial sphere in the depth of winter, one should spend a few clear nights in the rural districts of New York and new England.
Author’s note: Clearly, by the 1890s, light pollution was becoming a signifiant issue for urban dwellers in comparison to the darker skies of earlier times.
The reader is referred to maps 18 and 19 feaured on pages 92 and 93 of the text. Serviss begins with the large and winding constellation Eridanus the celestial River, so named by the ancient Greeks, though the Egyptians intended that it should really represent the majestic Nile. Only the northernmost stars are visible from the author’s far northerly latitude, where the opera glass sweeps up a good assortment of its stars including Beta, which forms part of the ‘foot’ or Orion near Rigel, but also the roughly linear array of stars comprising Gamma, Pi, Epsilon and Delta Eridani.
Fluvius (Latin for ‘river’) Eridanus, as it is affectionately known to this author, snakes its way over a prodigious 100 degrees of sky, as far south as the bright blue-white star, Achernar, some 57 degrees and 42 minutes south of the celestial equator and so hopeless beyond the ken of observers situated in the far north.
Seviss calls our attention to the remarkable multiple star system, Omicron (40) Eridani:
There are the two Omicrons, the upper one being o1 and the lower one o2. The latter is of an orange hue, and is remarkable for the speed which which it is flying through space. There are only one or two stars whose proper motion, as it is called, is more rapid than that of o2 in Eridanus. It changes its place nearly seven minutes of arc in a century.
Author’s note: The large proper motion of o2 Eridani is a sure sign that it is located relatively near the solar system. Indeed astronomers esimate that is a mere 16 light years away.
Though both o1 and o2 Eridani are quite easily seen with the opera glass, the deeper secrets of the orange star o2 are quite beyond its powers. o2 actually has two faint companions of magnitudes 9.5 and 10.5, which were both uncovered by Sir William Herschel, observing from Bath, England, onthe evening of January 31 1783. These can be resolved by a small telescope using moderate magnifications (discussed by Serviss on page 95). the brighter magnitude 9.5 star is actually a white dwarf, discovered to be such in 1910, while the fainter 11th magnitude component is now known to be a red dwarf star that orbits the white dwarf every 250 years or so. What an eclectic communion of suns!
From northern Eridanus, Serviss next turns his attention to two remarkable asterims higher up in the sky in Taurus; the Hyades and the Pleiades. Easily visible to the naked eye, these clusters of starlight are a delight to study with the opera glass as Serviss enthusiastically informs us. Concerning the illustrious Hyades he writes;
Many of these stars can be seen, on a dark night, with an ordinary opera glass, but, to see them well, one should use as large a field glass as he can obtain……Below the tips of the horns and over Orion’s head, there are also rich clusters of stars, as if the Bull were flaunting shreds of sparkling raiment torn from some celestial victim of his fury. With an ordinary glass, however, the observer will not find this star-sprinkled region around the horns of Taurus as brilliant a spectacle as that presented by the Hydaes and the group of stars just above them in the Bull’s ear.
This author has enjoyed many evenings observing the Hyades with his opera glass, or with modern binoculars. The rather restricted field (4.5 angular degrees) of view of the former will just accommodate the main part of the Hyades asterism, but it is still enough to soak up the beautiful ruddy tint of brilliant Aldebaran, and will show many of the brighter stars in the southern part of the characteristic ‘V’ shape, where the mind’s eye can indeed conceive of them as ” shreds of sparkling raiment,” as Serviss describes them. Indeed, close inspection with the opera glass reveals subtle colour differences between its constituent stars; orange, yellow and white.
His remarks concerning what can be seen in a larger ‘field glass’ are entirely valid however. For example, in a modern compact binocular, such as the author’s 8 x 42, the view of the Hyades is transformed immeasurably from that seen in the early 20th century opera glass, where many more stars are manifested owing to considerably greater magnification and a much wider field of view. In particular, the southern part of the asterism comes alive with dozens of faint stars like sparks falling from the fiery red coals of Aldebaran. Indeed, the view of the Hyades in a modern binocular offering a 7 or 8 degree true field is arguably one of the most fetching sights in all the heavens and one this author never tires of exploring!
On page 97, Serviss states that the Crab Nebula ( Messier 1) can be seen in a ” first rate field glass,” in the vicinity of Zeta Tauri.
Author’s note: Alas, I have been unable to detect M1 from my observing site using the opera glasses. Indeed, it is very challenging in the 8 x 42, but readily seen as a tiny nebulous speck in a 10 x 50 at the same site. The author did however detect the Crab from a darker setting in the southwest of Scotland using his 8 x 42 during a family vacation in October 2018. The fact that it is a difficult binocular object today probably reflects the darker conditions enjoyed by Serviss at the end of the 19th century.
On page 98, Serviss calls our attention to the subtle colour differences between Betelgeuse in Orion and Aldebaran in Taurus;
The redness of the light of Aldebaran is a very interesting phenomenon. Careful observation detects a decided difference between its color and that of Betelgeuse, or Alpha Orionis, which is also a red star……Aldebaran has a trace of rose-color in its light, while Betelgeuse is of a very deep orange.
Author’s note: This is indeed the case. As stated previously, the opera glass is a capital instrument to discern colours in stars. This author can readily detect a rose tinting in Aldebaran while the hue of Betelgeuse does indeed present as a very deep orange. This probably reflects the spectral differences between the stars (K5 and M1 respectively), which in turn are attributed to different absorption characteristsics of the gaseous matter in their outer atmosphere.
On page 100, Serviss launches into a fascinating discussion of the Pleiades with beautiful prose:
In every age and in every country the Pleiades have been watched, admired and wondered at, for they are visible from every inhabited land of the globe. To many, they are popularly known as the Seven Sisters , although few persons can see more than six stars in the group with the unaided eye. It is a singular fact that many of the ancient writers declare that only six Pleiades can be seen, although they will also assert that they are seven in number. these seven were the fabled duaghters of Atlas, or the Atlantides, whose names were, Merope, Alcyone, Celaeno, Electra, Taygeta, Asterope and Maia.
The mythology behind the Pleaides is not confined to the imaginings of the ancient Greeks though, for as Servss reminds us, the celestial fireflies feature richly in the lore of every nation under heaven. He writes:
They have impressed their mark, in one way or another, upon the habits, customs, traditions, language, and history of probably every nation. This is true of savage tribes as well as great empires.The Pleiades furnish one of the principal links that appear to connect the beginnings of human history with that wonderful prehistoric past, where, as through a gulf of mist, we seem to percieve faintly the glow of a golden age beyond.
Author’s note: The Genesis creation account states that when God first fashioned humans in His image from the dust of the ground, he became a living, breathing soul endowed with remarkable cognitive abilities(far in excess of any beast which, in itself, still presents an intractable problem for evolutionists). And sure enough, archaeologists have uncovered many cave paintings which affirm mankind’s long fascination with the stars, where the Pleiads are often depicted in highly accurate astronomical renderings. See this article for interest. Clearly these early people were no dummies!
Over the next few pages, Serviss delivers an excellent overview of some of the mytholgical lore associated with the Pleiades, particularly that of the ancient Egyptians but also mentioning the Hindus, Persians, Greeks, various south- and central-American cultures and even the Celtic Druids, which is of passing interest, but ultimately unrelated to observing. It is only on page 102 that he re-engages the interested reader with observational commentary, referring to a neat little diagram of the Pleiads on page 103;
With the most powerful field-glass you may be able to see all the stars represented in our picture of the Pleiades. With an ordinary opera-glass the fainter ones will not be visisble; yet even with such a glass the scene is a remarkable one. Not only all of the “Seven Sisters” but many other stars can be seen twinkling among them.
Author’s note: The low-power opera glass does indeed show many more stars (perhaps 15?) than can be seen with the unaided eye but is simply not powerful enough to discern the fainter members drawn on his diagram presented on page 103. Nonetheless, the opera glass still presents a beautiful and engaging image of this celebrated star cluster that is substantially eclipsed by modern binoculars with their higher powers and superior light throughput.
Serviss encourages his readers to learn the name and position of the main stars in the Pleaides before discussing some of the more interesting astronomical science associated with the asterism, particularly evidence associated with their common origin, which includes a common proper motion through interstellar space (see page 103). He even mentions a rather bizarre assessment made by the German astronomer, Johann von Mädler (1794-1874), who first put forth the idea that all the stars of the Pleiades revolved around Alycone, but which was later shown to be untenable. Immediately following this, Serviss embarks on a fascinating discussion of the existence of nebulosity around some of the stars in the Pleiades star cluster:
Still another curious fact about the Pleiades is the existence of some rather mysterious nebulous masses in the cluster. In 1859 Temple discovered an extensive nebula, of a broad oval form, with the star Merope immersed in one end of it. Subsequent observations showed that this strange phenomenon was variable. Sometimes it could not be seen; at other times it was very plain and large. In Jeaurat’s chart of the Pleiades, made in 1779, a vast nebulous mass is represented near the stars Atlas and Pleione. This has since been identified by Goldschmidt as part of a huge, ill-defined nebula, which he thought he could perceive enveloping the whole group of the Pleiades. many observers however, could never see nebulous masses, and were inclined to doubt their actual existence. Within the past few years astronomical photography, having made astonishing progress, has thrown light upon the mysterious subject. The sensitized plate of the camera, when applied at the focus of a properly constructed telescope, has proved more effective than the human retina, and has, so to speak, enabled us to see beyond the reach of human vision by means of the pictures it makes of objects which escape the eye. In November 1885, Paul and Prosper Henry, turned their great photographic telescope upon the Pleiades, and with it discovered a nebula apparently attached to the star Maia. The most powerful telescopes in the world had never revealed this to the eye.
Author’s note: The reflection nebula around Merope was uncovered by Wilhelm Temple using a modest 4 inch achromatic refractor. Historical documents do indeed show that this nebulosity was notoriously difficult to discern visually, especially with large, observatory-class instrumets. One record shows that the celebrated double star observer, S.W. Burnham, failed to see any nebulosity around Merope using a much larger refractor than anything Temple had access to and so expressed doubt of its existence. It was spotted by E.E Barnard though. Such stories are not unique to the Merope Nebula, as similar anecdotes have been reported concerning the Rosette Nebula in Monoceros, which is much better seen in a small, rich-field telescope than a large one with a restricted field of view.
The author is uncertain as to the precise photographic telescope used by the brothers Henry referenced by Serviss above, but it was probably a fore-runner to their 33cm and larger 62cm astrographs used by astronomers at Paris and Meudon Observatory, respectively, in the 1890s. For more information please see chapter 26 on the Great Meudon Refractor in the author’s book, Chronicling the Golden Age of Astronomy (Springer Nature 2018).
On page 106, Serviss begins to create many charming word pictures of the ruling constellation of winter; Orion. He writes;
To the naked eye, to the opera glass, and to the telescope, Orion is alike a mine of wonders. This great constellation embraces almost every variety of interesting phenomena that the heavens contain. Here we have the grandest of the nebulae, some of the largest and beatifully colored stars, star-streamers, star-clusters, nebulous stars, variable stars.I have already mentioned the positions of the principal stars in the imaginary figure of the great hunter….. Betelgeuse, it may be remarked is slightly variable. Sometimes it appears brighter than Rigel, and sometimes less brilliant. It is interesting to note that, according to Secchi’s division of the stars into types, based upon their spectra, Betelegeuse falls into the third order, which seems to represent a type of suns in which the process of cooling , and the formation of an absorptive evelope or shell, have gone on so far that we may reagrd them as approaching the point of extinction.
Author’s note: Even at the end of the 19th century, it is clear that astronomers had already envisaged an evolutionary sequence of events that causes stars to change throughout their lives. Secchi’s primitive stellar classification sheme gave way to the more elaborate Hertzsprung-Russell scheme, where a robust physical theory underpinned this change, greatly aided by the genius of Sir Arthur Eddington, who’s seminal work established the physics of stellar interiors and who clearly demsonstrated how they change as a function of time. Betelgeuse is indeed at the end of its life and is fated to explode in a cataclysmic supernova event. It might have already happened, for we would have no knowledge of the event for 500 years, which is the time taken for its light to reach us. Mighty Betelgeuse is a mammaoth star, whose diameter exceeds that of the orbit of Mars.
Serviss continues his discussion on the bright luminaries of Orion by contrasting fiery red Betelegeuse with brilliant white Rigel;
In Rigel we see a sun blazing with the fires of youth, splendid in the first glow of its solar energies, and holding the promise of the future yet before it. Rigel belongs to a new generation of the universe; Betelgeuse to the universe that is passing.
Author’s note: In Serviss’ day, astronomers believed stars started out their lives shining in white or blue-white hues, but as they aged they cooled off into yellow and finally red suns. This is the reason why some old-school astronomers still refer to the whiter stellar varieties as ‘early’ and their ruddier counterparts to be ‘late.’ In reality though, stars vary greatly in their longevity. Small stars, like the exceeding abundant red dwarves, which comprise perhaps 80 per cent of all suns in the Creation, can maintain a stable existence for trillions of years. The largest, in contrast, are fated to self destruct in just millions.
The lifetime of a star is dictated by its mass and scales as (Mo/M)^2.5, where M is the mass of the star and Mo is the mass of the Sun. It follows that while Betelgeuse, with an estimated mass of ~ 12Mo will have a lifetime of (1/12)^2.5 or just 0.2 per cent of the Sun’s lifetime (~10 Gyr). This fits well with its estimated age of ~ 10Myr.
Turn your glass upon the three stars forming the Belt. You will not be likely to undertake to count all the twinkling lights that you will see, especially as many of them appear and disappear as you can turn your attention to different parts of the field.
Author’s note: The ~4.5 degree field of view of the opera glass easily fits the three belt stars in the same portal and is a joy to behold on a dark, winter night. The glass reveals that all three stars appear white, reflecting perhaps their common origin from a larger, so-called OB Association. From left to right these stars are given majestic names; Alnitak, Alnilam and Mintaka. Arranged as a slanting line, they naturally create the illusion of being at the same distance but this is, once again, a pleasant fiction; Mintaka is both fainter and nearer than the other two belt stars, which are situated about three times further away.
The belt stars actually form part a much grander arrangement of suns known collectively as Collinder 70. Held steadily, the opera glass will reveal a swarm of fainter stars, many of which are of the 6th and 7th degree of glory, in and around the three belt stars. When observed with a modern 10 x 50 binocular, Collinder 70 is a breathtaking sight! The reader is best advised to wait until the constellation culminates over the southern horizon to make the most at teasing the fainter members of Collinder 70 out of the murk, as they are more easily picked off with increasing altitude.
Serviss continues his description of the winter sky with an in-depth look at Sirius, the brightest star in all the heavens:
Sirius, in fact, stands in a class by itself as the brightest star in the sky. Its light is white, with a shade of green, which requires close watching to be detected. When it is near the horizon, or when the atmopshere is very unsteady , Sirius flashes primatic colors like a great diamond. The question has been much discussed , as to whether Sirius was formerly a red starIt is described as red by several ancient authors, but it seems to be pretty well established that these descriptions are most of them due to a blunder made by Cicero in his translation of the astronomical poem of Aratus. It is not impossible, though it is highly improbable, that Sirius has chnaged color.
Sirius does indeed corruscate wildly in the dense air near the horizon at my far northerly latitude. The colours of Sirius seen by the naked eye and through the opera glass reveal the complex interplay between brilliant star light and atmospheric refraction. The very idea that Sirius was once a red star seems altogether unlikely to me and Serviss’ pointing to Cicero’s “blunder”, as it were, seems entirely reasonable as the explanation as to why this myth has been perpetuated throughout the centuries.
Serviss invites the reader to look at Sirius with the opera glass and its interesting hinterland. Indeed, by placing Sirius toward the top of the field, my opera glass picks up the faint glow of Messier 41 – discussed by Serviss on page 112 – at the bottom of the field of view. Serviss states that this open cluster is best seen with ” powerful opera glasses or a field glass.”
Author’s note: Although many observers more conveniently located further south rightly describe M41 to be a rather spectacular sight in larger binoculars or a small, rich field telescope, it’s very low altitude at 56 degrees north latitude detracts significantly from its visual punch.
Serviss then discusses the discovery of the elusive companion to Sirius, how it was predicted by Friedrich W. Bessel before finally being unveiled in the winter of 1862 when it was discovered through a large achromatic refractor fashioned by Alvan Clark. In the closing pages of his treatise on the “Winter Stars,” Serviss discusses some low lying objects that can be reasonably seen with a field glass from mid-northern latitudes eg. M46 in Puppis, but for some reason, fails to bring our attention to Messier 50, easily picked up in my lowly opera glass as a foggy 8th magnitude patch about half the size of the full Moon, about one third of the way from Sirius towards Procyon, but does rightly acknowledge an interesting field of stars (8, 13 and 17 Monocerotis), near its northern border. He ends the chapter with a clarion call for us to become observers of the sky:
Do not be afraid to become a stargazer. The human mind can find no higher exercise. He who studies the stars will discover-
“And endless fountain of immortal drink
Pouring unto us from heaven’s brink.”
That’s regal advice for anyone in any time!
Chapter 1: The Stars of Spring
Covering pages 7 through 29
Having selected your glass, the next thing is to find the stars. Of course, one could sweep over the heavens at random on a starry night and see many interesting things, but he would soon tire of such aimless occupation. The observer must know what he is looking at in order to derive any real pleasure or satisfaction from the sight.
Serviss begins his overview of the spring sky with a rather bold assertion; haphazard scanning of the heavens with an opera glass is something observers will soon tire of. I respectfully disagree with Serviss in this matter, as I rather enjoy sweeping up starfields, moving randomly one way, and then another, ‘discovering’ new and interesting configurations of stars, unnoticed asterisms as it were, that I may happen to chance upon. What is more, I have come to view all of my binoculars as providing different sized portals on the night sky, with each one opening a unique window on the darkness of space.
When it comes to stargazing, getting lost can be an exciting prospect!
The next few pages of the book cover the basics of how the sky works in beautiful prose, as well as how to get started by learning some of the key signposts that point the way to interesting parts of the spring sky. Serviss urges his readers to take the time to learn how to recognise the main constellations of the vernal heavens:
In the same way you will be able to find the constellations Cassiopeia, Cepheus, Draco, and Perseus. Don’t expect to accomplish all in an hour. You may have to devote two or three evenings to such observation, and make many trips indoors to consult the map (see page 8), before you have mastered the subject; but when you have done it you will feel amply repaid for your exertions, and you will have made yourself silent friends in the heavens that will beam kindly upon you, like old neighbors, on whatever side of the world you may wander.
On page 11, Serviss offers some good advice regarding the attainment of a steady, comfortable view, recommending for example, a convenient arm rest and a “lazy back chair.” He then mentions something quite notable:
Remember that no two persons’ eyes are alike, and that even the eyes of the same observer occasionally require a change. In looking for a difficult object, I have sometimes suddenly brought the sought-for phenomenon into view by a slight turn of the focusing screw.
Author’s note: I can certainly affirm what Serviss is saying here. The eye can vary somewhat in its degree of accommodation of an image and it has become his custom to keep his hand on the focusing wheel while viewing an object, tweaking it ever so slightly to get the optimal focus.Small chnages can indeed yield dividends, especially on fainter open clusters and nebulae. Of course, changes in altitude also require routine re-focusing.
To be continued…….
In this day and age, where almost every item of equipment we use under the stars is taken for granted, it pays to remember that we have a lot to thank our astronomical forebears for. A case in point is the humble Barlow lens, which has enjoyed a very long and illustrious history with visual observers, where today it remains an indispensable tool as well as a cost-saving device for the amateur astronomer.
Contrary to popular belief, the concept of the Barlow lens does not reside entirely with the musings of the English mathematician Peter Barlow (1776-1862), but actually had its origination in the fecund mind of the 18th century German philosopher and mathematician, Christian Wolff (1679-1724), who first conceived of the idea of adding a concave lens ahead of the eyepiece but behind the objective of a telescope in order to provide greater magnification and with a slight increase in focal length. The result had mixed fortunes however, in that the resulting images in an achromatic telescope, while certainly enlarging the image, also deteriorated the achromatism achieved by the combination of the crown & flint object glass.
The problem was once again studied with renewed vigour in the first half of the 19th century, when Peter Barlow, then a Professor of mathematics at the Royal Military Academy, Woolwich, England, computed the design of an achromatic concave lens which was made by the optician, George Dollond, and mounted in a telescope where it showed very promising results. Some of the earliest ‘guinea pigs’ to experiment on the new device included the Reverend William Rutter Dawes and the Admiral William H. Smyth, who both commented favourably on the new contraption as early as the late 1830s and early 1840s, reporting that the image was left just as colour free as when the telescope was used without the contrivance, even allowing them to vary the magnification at will by moving the doublet lens either towards or away from the ocular lens.
The device, now commonly known as the Barlow lens, enjoyed rapid success. This author is reminded of the work of the astronomers serving in the employ of the Victorian tycoon, George Bishop, who had set up a lavishly-equipped private observatory in 1836 at South Villa, Inner Circle, Regent’s Park, London, where the Barlow lens is vividly described:
An achromatic lens( the macro-micro lens), which slides into the tube of the micrometer, was frequently used by Mr. Dawes in his observations of double stars. The effect of the interposition of this lens is to increase the magnifying power nearly in the ratio of two to one, without any very serious diminution of light. It is, therefore, of great service in the measurement of difficult objects which require increase in power with considerable light.
xii-xiii Bishop, G., Astronomical Observations Taken at the Observatory , South Villa, Inner Circle, Regent’s Park, London, During the Years 1839-1851
How does a Barlow work? Because it is a negative(diverging) lens consisting in its most basic form as either an air-spaced or cemented crown-flint doublet, it changes the angle of convergence, making it longer, as though the beam were coming from an objective lens or primary mirror with a longer focal length. What this means in effect is that a 2x Barlow will double the effective f ratio of your telescope, turning an f/5 system into an f/10. And though the Barlow lens can introduce some additional errors into the optical train, if well made, it will almost certainly remove more aberrations than it generates. This is easy to see when using an ordinary eyepiece, such as a 20mm Plossl or some such, in a fast optical system like my two Newtonian reflectors. Used without a Barlow lens, the 20mm Plossl will give very good on-axis performance but less so off-axis. Now insert a 2x Barlow lens ahead of the eyepiece and the off-axis performance is considerably improved! That’s because the cone the eyepiece ‘sees’ looks like an f/10 optical system and not an f/5 system.
In the days before anti-reflection coatings, Barlow lenses caused a small but noticeable reduction in image brightness, as well as the odd ghost image due to internal reflections, especially on bright objects, but with modern multi-coatings appplied to all air-to-glass surfaces, this light loss is reduced to negligible levels(~3 per cent).
Barlows come in all shapes and sizes, offering magnification boosts in the range of 1.6x right up to 5x. That said, by far the most commonly used Barlow lenses offer powers of either 2x or 3x. In general, longer Barlow lenses tend to give greater magnification boosts than shorter ones, but there are always exceptions.What is more, the power printed on the barrel may not be the power you get in field use, but it’s normally quite close. In addition, with refractors that employ 90-degree star diagonals, a 2x Barlow used in normal mode can also give a 3x boost if screwed into the front of the same diagonal. Bear in mind though that most modern Barlow lenses are intended for use at the power they show on the barrel and may not perform quite so well when moved to provide a different magnification. One should always avoid models offering a range of magnifications by moving the optics in a sliding tube, for example.
The Barlow lens has the inherent property of increasing the eye relief of any eyepiece used in combination with it. This is of considerable advantage to those who enjoy very short focal length Plossl and orthoscopics, for example, which by nature offer amounts of eye relief broadly similar to the focal length of the ocular used and thereby improving the degree of viewing comfort experienced by the observer.
With my fast (f/5) Newtonian telescopes, I have found through experience that shorty Barlows are better than their longer counterparts, because they always reach focus with them.That said, shorty Barlows also increase eyerelief more than longer Barlows. I have used this to great effect in my study of double stars with a 130mm f/5 and a much larger 305mm f/5 Newtonian. For example, when combined with one of my favourite eyepieces used to resolve close binary systems; a Parks Gold 7.5mm ocular, a 3x Meade shorty Barlow provides a supremely comfortable field of view at 260x in the 130mm telescope with wonderful, edge-to edge-sharpness.
Another favourite with a Barlow lens is my old 4.8mm T1 Nagler. This high power eyepiece delivers a magnification of 135x in the 130mm f/5 by itself but the eye relief is quite tight. All that changes though when I use it in conjunction with my 2x or 3x Barlow lenses (yielding powers of 270x and 405x, respectively). Eye relief is much improved and the views that little bit more enjoyable!
When Barlowing longer focal length eyepieces, care must be taken to ensure it does not strongly vignette the outer part of the eyepiece field. If the field stop of the eyepiece is greater than the clear aperture of the Barlow, then it will cut off some of the light coming from the outer sections of the eyepiece, resulting in significant light loss and a reduction in the true field presented. Look at the two Barlows shown in the image below, for example. The Barlow shown on the left is the Orion 2x shorty Barlow and the one on the right is the 3x Meade Barlow. Note the larger clear aperture of the former, which makes it better suited for magnifying low-power, long focal length oculars.
In recent years, a number of firms have brought to market so-called “apochromatic” Barlow lenses with some kind of low dispersion glass included in the prescription. These can often be sold at higher prices than regular, “achromatic” Barlow lenses with the implication that they will perform better. This is nonsense however, as a good achromatic doublet with properly applied anti-reflection coatings will give essentially the same performance. Indeed, one of the first ‘apo’ Barlows this author has experienced; the Meade # 140; performed significantly worse in field tests than a standard achromatic system costing half as much! The truth of course, is that the introduction of apochromatic Barlows is yet another clever marketing gimmick that has caught more than a few tyros off guard. As proof of concept, consider the excellent Barlow lenses long offered by well established firms such as TeleVue, who make some of the best long Barlows money can buy. You won’t have to look long to see that all of the Barlows Albert Nagler has brought to market are well-made achromatic doublets. If there were an advantage of including low dispersion glass in their prescription, don’t you think Uncle Al would have done it long ago?
Nor will a Barlow lens improve the colour correction of an achromatic refractor, as some amateurs have claimed on the vulgar forums. The dispersion caused by the achromatic doublet is completely unchanged when using a Barlow lens. Neither will it increase the depth of focus of the telescope when used normally. That said, Barlows can certainly help achieve larger fields that are corrected for the Seidel aberrations such as coma, for example, which can be mildly annoying to those who use fast f/4 and f/5 relative apertures.
Consider a case in point: the coma free field of a Newtonian system in millimetres, scales directly as the cube of focal ratio. Specifically;
The coma free field = 0.022 x f^3.
So, for my f/5 Newtonian we obtain a coma free field = 0.022 x 5^3 = 2.75mm.
Next, consider how this translates into true field.
True field in radians is given by; coma free field/ focal length.
Thus, the true coma free field in the 650mm Newtonian will be:
(2.75/650) = 0.0042 radians, and then converting to angular degrees gives 0.0042 x 360/2pi = 0.24 degrees.
Consider next a typical high−power eyepiece used in double star divination. As mentioned above, one of my favourite combinations for close double star work is a 7.5mm Parks Gold coupled to a 3x Barlow lens, with an apparent filed of view of about 50 degrees. This yields a power of 260 diameters in the 130mm f/5, so the coma free field at this enlargement is: 260 x 0.24 = 62.6 degrees!
This means that there is no coma to worry about across the entire field of view using this particular configuration. Barlows will similarly reduce the effects of other Seidel aberrations in similar fashion(though to a varying degree corresponding with how those said aberrations fall off with focal ratio). This helps keep the images of the stellar disks nice and crisp as they move from one side of the telescopic field to the other.
Barlow lenses are cost-saving devices too. Indeed, a savvy telescopist can dispense with acquiring a complete set of half a dozen eyepieces say, and instead choose just two or three oculars and a Barlow lens(or two) to achieve the range of magnifications one desires from the telescope. For example, if you have a 25mm and 8mm Plossl, as well as a 2x Barlow used with a telescope with a focal length of 800mm, you can get a nice range of powers; 32x, 64x, 100x and 200x.This is especially true since good Barlow lenses can be had for considerably less money than a fixed focal length eyepiece. My own Barlow lenses cost between £20 and £30 and perform handsomely with virtually all eyepieces I couple them to.
For those folk who dislike the change in eye relief caused by a Barlow lens they should consider telecentric devices like those marketed by TeleVue( the Powermate) and Meade. These will not increase the eye relief you get with a given ocular and also maintain the same focus position one enjoys when the eyepiece is used alone. They are however, considerably more expensive than regular Barlows.
Barlows also have a very important role to play in astro-imaging, particualrly high-resolution lunar and planetary photography, where they provide very effective focal length boosts and thus an appropriate image scale. They are also supremely useful in binoviewing, by decreasing the amount of in-focus travel necessary to achieve focus with many of these devices.
So, in summary, Barlow lenses serve as very important tools for the modern visual observer and imager alike, and are thus very unlikely to go out of fashion any time soon. Good ones can be had fairly inexpensively and will provide the user with a lifetime of applications.
Neil English is author of Choosing and Using a Dobsonian Telescope.
Not all binoculars are created equal. Some match the advertisement claims, while others do not. In this blog, I’ll be exploring optical and mechanical features that I like in a hard-working binocular and whether or not the price paid for a binocular matches its performance in the field.
Coatings & Baffles:
Okeydokey. Let’s get started.
The reader will note that all the binoculars (featured above) are meant to be fully multi-coated. Here is what I understand the term to mean:
All glass surfaces have multiple coatings and it is the best kind, resulting in light transmission of 90-95% for bright, sharp and contrast images.
In the first investigation, I performed a bright light experiment to test for;
1. On-axis ghost images which is a sensitive test of the quality of the anti-reflection coatings applied to the optical components within the binoculars.
2. Off axis flaring which tests how good light baffling works in the instruments.
The light source needs to be small and as bright as possible. For this, I elected to use the torch on my iphone with the setting set to maximum. The ambient light was dimmed by pulling my living room curtains in such a way as to leave a small amount of daylilight to illuminate background objects. As well as looking for on-axis reflections and off-axis flare, I studied how well defined the images were immediately behind(backlit) and around the light source.
All the binoculars can be sharply focused at the close distance chosen for the test(~3 metres) and all the images were performed at the position of sharpest focus.The experiment was performed using both eyes separately to check that the effects noted were in any way dependent upon the eye barrel used.
To quantify the effects I chose a number scheme from 1 through 10, with 1 representing very poor perfomance and 10 being sensibly perfect. It must be noted that no binocular, no matter how well appointed, can achieve a 10 score. Even the very best instruments display some degree of unwanted internal reflection and/or off axis flaring. Thus, to expect none at all is quite an unreasonable proposition.
Instrument On-axis internal reflections Off-axis flaring
Nature DX 2 4
Pentax DCF 5 6
Opticron Aspheric LE 4 5
B&S Sierra 8 8
B&S Savannah 8 9
No significant differences between the left and right barrels were uncovered. The results documented are thus representatve for both eyes.
All the binoculars gave acceptable results with the exception of the Celestron Nature DX. The on-axis internal reflections were very strong and bright, with some reflections taking up quite a bit of the field of view. This made imaging backlit objects very difficult. If this is a fully multi-coated binocular then my name is Mickey Mouse. Off-axis flaring was also the strongest in this unit.
To my suprise, the Opticron proved less effective than I had expected with a few fairly prominent reflections on-axis but noticeably better off-axis performance. It was overall however, in a different league to the performance exhibited by the Celestron unit.
The Pentax also suprised me as I expected it to have the best performance, based solely on its reputation for quality and the not inconsiderable price I paid for the unit. It displayed one bright, unwanted reflection on-axis, but had improved off-axis performance in comparison to the Opticron unit. In addition, the definition of backlit objects was considerably improved in both the Pentax and Opticron units over the Celestron.
To my surprise and delight, both the Barr & Stroud Sierra 10 x 50 and the 8 x 42 Savannah showed much more subdued on-axis reflections than the Opticron and Pentax. Instead of bright spots, both these binoculars gave very much more subdued reflections. They were certainly present but with far lower intensity. Off-axis performance was also very impressive, with the nod going to the Savannah. Backlit definition was also excellent in both these instruments. The reader will also note that larger aperture instruments collect more light and so might be expected to have more on-axis internal reflections and off-axis flaring than the smaller aperture binoculars tested. That this was not found to be the case in both the Barr & Stroud units was quite remarkable!
Conclusions: Buyers should be wary of marketing claims. The Celestron Nature DX clearly has inferior coatings to the other instruments tested and is certainly not fully multi-coated in the same way as all the other units were. This is in keeping with its low price(the lowest of all the instruments tested) and could be said to be an acceptable tradeoff owing to its very low street value (£59 paid). Still the result is rather worrying, as I would reasonably expect the larger DX models to be manufactured in much the same way, and so they may have undergone the same shortcuts somewhere in their construction. Any owners of larger Nature DX binoculars need to check(don’t go all proud on me!) this out and report to the amateur community.
Considering the price paid for both the Barr & Stroud units was about the same as the Pentax binocular(in fact, the Savannah, which I purchased secondhand cost me significantly less), I feel they both offer excellent protection against internal reflections and are very well baffled. Whoever made these units knew what they were doing and properly executed the technologies available to them.
So you don’t always get what you pay for.
A general note on on coating tests: If you’re a binocular collector, why not perform your own set of tests on them to see if they show evidence of sub-standard anti-reflection coatings? I would expect older models to fare worse in such tests e.g. vintage binoculars made in the post-war era and the like.
A general note on baffling: It occurred to me that while baffling is an important design feature in a good binocular, it is possible to over do it. A well baffled instrument produces images that are richer in contrast than an instrument with inadequate baffling, all other things being equal. But manufacturers can deliberately over baffle the light path with the aim of maximising the punch of an image, but at the expense of cutting off a little too much light and thereby restricting its effective aperture. This may go some way to explaining why some models in the same price range can display significantly different images, some over-emphasing baffling to generate the maximum contrast but where the images are a tad dimmer, and those that produce brighter images but with less aggressive baffling. Since many birders use their binoculars during daylight hours, an aggressively baffled instrument may be judged as having higher contrast, but during more critical testing during low-light conditions or viewing the night sky, its restricted aperture may become more noticeable.
The effects of recess depth in binocular objective lenses: Small design features can make meaningful differences to the quality of the images garnered by a binocular. In this section, I would like to discuss the importance of having objective lenses recessed from the front of the instrument in order to minimise the effects of stray light entering the optical train during bright, daylight operations.
What I’m effectively talking about here is what a lens shade or hood does. The function of such a device is to reduce lens flare comng from the peripheral field as illustrated below for a camera lens;
It also doubles up to provide some protection of the object glass during adverse weather conditions, such as occurs in rain, mist and when side winds bring air-borne dust and other materials with them.
For the sake of brevity, I will only illustrate the two extremes in the binoculars discussed here. First take a look at the very deeply recessed lenses on the Barr & Stroud Savannah. It measures 7mm!
Contrast this to that found in the Ceestrobn Nature DX binocular, which had a measured recess of just 3mm.
For the record, the others fared as folllows;
Barr & Stroud Sierra: 5mm
Pentax DCF: 4mm
Opticron Aspheric LE: 4mm
It is the opinion of this author that having a reasonably functioning lens shade does improve image contrast in daylight images, especially when viewing under bright, sunlit conditions. I was very glad to see that the Barr & Stroud instruments were, yet again, well appointed in this regard. It’s yet another small touch that will be appreciated by an avid binocular enthusiast.
The importance of good quality eyecups: Good eyecups make for comfortable, immersive binocular viewing. If too flimsily made, they can be uncomfortable to set your eyes against, or fall out of position when twisted up. For me, there is nothing more frustrating than to have to readjust the eye cups on the fly while making observations. Cheaper models invariably come with crudely made plastic cups that quickly lose their rigidity after a few weeks of hard use. Better made eyecups usually come in the form of metal-over rubber and can be set to a variety of positions that hold there, even when a little pressure is applied to them, either by touching them with your fingers or pressing your eye up to them when conducting an observation.
Of the binoculars considered here, three are particularly worthy of a few words; the Pentax DCF, the Barr & Stroud Sierra and Savannah.
The Pentax DCF has good quality eyecups. They provide the user with a choice of four positions and so can accommodate virtually anyone, either without glasses or with them on. They also stay in place when pressure is applied to them. My only gripe is that they they do have a bit of play in them and could be a bit more rigid.
The Barr & Stroud Sierra and Savannah have significantly different eyecups as the photo below reveals:
Both use metal-over rubber. Those found on the Sierra model are typical of what you’d find on a mid-priced binocular of this size. The eyecups click nicely into place, offering three positions for optimal eye relief. They are sufficiently well made to last indefinitely if properly cared for. That said, once again, the Savannah really surprised me! Specifically, the eye cups are far more rigid than in the Sierra and click into place with a commanding “kathud” sound. What I found remarkable is that there is very little play to to be had with them. Once clicked into place, they stay in place. You’ll never have to worry about them slipping out of position while using the instrument.
What does this buy you?
Peace of mind!
Now, I’m not saying that the quality of the eyecups on the Savannah is in the same league as those beauties made by Leica and Swarovski( I recently enjoyed the use of the 8.5 x 42 Swarovski ELs), for example, which are works of art, both mechanically and ergonomically, but I doubt anyone would be unimpresed by such high quality eyecups on the Savannah. Indeed, you simply won’t see this kind of quality on any mid-priced binocular that I know of. They are dependable, rigidly set, and a joy to use in the field.
Thoughts on Dioptre Adjustment:
Most roof prism binoculars have their dioptre adjustment setting under the right ocular lens. It usually involves twisting a ring either clockwise or anti-clockwise, as appropriate, until both eyes show a perfectly sharp image. This works very well indeed, but some dioptre adjutsment rings are either too stiff or too loose, with the result that tweaking it and maintaining its precise positioning can be problematical. High-end, premium models such as those made by Leica and Swarovski cater especially well for the individual in that one can lock in the correct dioptre position by pushing the focuser forward, dialling in the correct dioptre setting, and then pushing the focusing knob back into place, thereby settin it permanently. This is ideal and a very clever mechanical solution.
The Barr & Stroud Savannah binocular uses a very different strategy however, by placing the dioptre adjustment on a dial just ahead of the focusing wheel as shown below:
As I explained in a previous blog, I find myself tweaking the dioptre setting fairly frequently and I have elected to do this by using bright stars in the night sky rather than using a terrestrial target. The reason I do so is that I have found that bright daylight targets present an overwhelming amount of visual information to the eye and though you can usually get very close to perfect, I have found small but consistent discrepancies between the position I chose by day and where it is adjusted to at night. Focusing on a bright point source such as a star yields an easy way to remove that ambiguity. I simply look for the tiniest, brightest star images the right barrel can provide.This has become my default custom when using the instrument for star gazing.
But doing this using a dioptre adjusting ring positioned immediately under the right ocular can be a little awkward and sometimes a bit frustrating, especially if the dioptre ring is stiff. In contrast, it is very easy to move my finger forward just a little to adjust the dioptre setting on the Savannah unit, allowing very precise tweaking of the dioptre setting to be made. I think this is a very well thought-out design feature on the Savannah that is not found on many other models.
A Strong Bridge: The design of the bridge mounting the two barrels of the binocular also has an impact on how well it operates in the field. Specifically, if the hinge is too loose, you will have to readjust the IPD every time you use it; not a deal breaker in its own right, but slightly inconvenient. Much better is a binocular that holds its IPD precisely from viewing session to viewing session. The Nature DX is quite stiff, as are the Barr & Stroud instruments, but the Pentax DCF and Opticron units are a bit too loosely mounted in my opinion.
The Savannah binocular in particular, has a very strong bridge, such that I have never needed to readjust it when it is taken out of its case. And when you consider that I’ve literally done this hundreds of times since I acquired in the autumn of 2018, I’d say that’s pretty good going! No faffing about, just remove from case, remove the lens caps and you’re good to go!
The value of a good carry strap: The carrying straps that come with many binoculars( even some mid- to high-end models) are of poor general quality. They’re usually made of poor quality plastic-based materials and fray easily. Having a good quality, padded strap is a far better option going forward, as the more comfortable the strap, the more you’ll likely use your binocular. In addition, cheap straps cut into your skin more and in hot weather can even cause heat rash and some blistering. One of the first things I’d recommend in upgrading a binocular is to invest in a more durable, high-quality strap.
The straps that come with all of the binoculars I have discussed, with the exception of the Barr & Stroud Savannah, are of generally poor quality and could well do with upgrades. This is something I hope to do remedy over the coming months. The Savannah comes with a nice, padded strap that is very comfortable to use and will not come apart in rough field use. It was a standard accessory with the binocular; complete with the Barr & Stroud logo; a nice touch for sure and something that can only be appreciated by using the instrument for prolonged lengths of time.
Recommending an all-purpose binocular to the masses: We’ve now reached the end of this blog and it’s an appropriate time to reflect on what a quality binocular should behave like. As you can gather, I am very enthusiastic about the Barr & Stroud Savannah in particular, as a full-featured instrument that includes a lot of nice touches but at a price that won’t leave you short of breath(it retails in the region of £120-140 UK). Optically excellent(with a whopping field of view of 143m@1000m or an 8.2 degree field), water proof, and built like a tank (it tips the scales at 810g) with a 10 year warranty, the company has clearly gone well beyond the call of duty to deliver a high quality instrument that will stand the test of time. Indeed, I was so enthusiastic about this particular unit that I ventured onto the vulgar forums to give my vote to it and also to sing a wee tune:
Oh I do like to be beside the seaside
Oh I do like to be beside the sea….
Oh I do like to stroll along the prom prom prom
Where the brass band plays diddleyumpumpum.
I also suggested there that someone else put this binocular to the test; someone honest and experienced that doesn’t hold grudges against other people.
If that’s YOU, then you’re in for a pleasant surprise!
Neil English was born at an early age and is Professor Emeritus of Tomfoolery from the University of Life.