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:
I stood expecting, in the gallery,
On which shine down the Heaven’s unnumbered eyes,
Poised in mid air by art and labour wise,
When with mind’s toil mechanic skill did vie,
And wealth free poured, to build that structure high,
Castle of Science, where a Rosse might raise
(His enterprise achieved of many days)
To clustering worlds aloft the Tube’s bright eye.
Pursuing still its old Homeric march,
Northward beneath the Pole slow wheeled the Bear,
Rose over head the great Galactic Arch;
Eastward the Pleaides with their tangled hair;
Gleamed to the west, far seen, the Lake below;
And through the trees was heard the River’s flow.
Sir William Rowan Hamilton, Parsonstown, August 29 1848
On our trip to the Emerald Isle, we spent a day in the grounds of Birr Castle, home of the famous Leviathan of Parsonstown.
It was a home-coming in more than one way.
Tune in soon to read the full story……….
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 praeternatural 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 in the main ‘V’ of the Hyades 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 scientific consensus is shifting considerably from this rather naive, simplistic view of life and whether it can arise on other worlds. Simply put, if life does exist on other planets; it was placed there, not by a string of false gods, but the only true and living God, who holds eternity in His hands; the God of the Bible. As this author has explained elsewhere, Serviss’ view of humanity as “contemptibly insignificant” is almost certainly false. We are, very likely, the only sentient creatures ever to have been created aide from the angels, and the Old Book proclaims that some of us will some day judge some of them! Apart from the Creator, there is no one to save us from ourselves; no super-advanced civilisation to bail us out.
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.
To be continued…….
With some sage commentary from former Sky & Telescope columnist, Gary Seronik.
Binoculars are indispensable tools for the naturalist and amateur astronomer. Their strength lies in their ease of use, low-power, wide-field views of the Creation, whether terrestrial or celestial. In this era of high technology, there is a huge number of models to suit just about everyone’s needs, wants and budgets. Content with my old 7 x 50 porro prism binos for three decades, I came to realise recently that it would be good to get a newer model that was better suited to my life circumstances.
I had grown older you see, with the result that the maximum diameter of my pupil could no longer open to 7mm. I became less tolerant of the fairly substantial weight of the 7 x 50s too, especially when I took some time out to relax on a recliner in my garden to gaze upon the heavens for prolonged periods of time. The 7 x 50s also suffered some knocks over the years and once they were fully submerged when I accidently slipped on some moss and fell into Loch Lomond lol. Luckily, though a source of considerable hilarity to my travelling companions, the ordeal wasn’t the end of the world, and though the prisms became mis-aligned, I managed to get them repaired at reasonable cost.
But what really catalysed my desire for a new binocular was the recent acquisition of an inexpensive 10 x 50 binocular I received in a swap (barter) for an eyepiece with a fellow amateur. At first I was thrilled with the 10 x 50s. They had a suitable exit pupil (calculated by dividing the diameter of the objective by the magnification), but they were quite heavy and owing to their ‘fully coated’ specifications, manifested significant light loss and reduced contrast owing to the presence of internal reflections when pointed at a bright light source.
I knew what I wanted going foward though. The binocular needed to be light weight but not feather-weight, as my experience with small compacts were somewhat less than inspiring. Somewhere between 600 and 700g would be ideal. The instrument had to be fully muti-coated to reduce light scattering inside to an absolute minimum. I could dispense with ED glass, as at the magnifications I intended to use the binocular at, I would be very hard pressed to see any secondary spectrum and I wasn’t going to splash out on an optical feature I could’t readily see! Much more important for me was that the binocular be well made and have a secure, rugged feel to them in field use.
I considered field of view too; at least 7 angular degrees but not overly wide since I reasoned that although some models were being offered with impressively wide fields up to 8 angular degrees or more, they would likely suffer more from off-axis aberrations that I would notice in field use.
Many of the ‘premium’ models also had features that I could readily do without as well: a slightly flatter field at the edge of the field, for example, or faster, smoother focusing that might be somewhat more important for observing fast moving wildlife at close hand; or a lockable diopter setting; those kinds of things.
Waterproofing would be a bonus, for sure, but not essential, as I don’t spend my days wading through swamps in search of feathered friends lol!
I decided that a full-size 8 x 42 roof prism binocular was the way to go. I was delighted to see that even very highly respected brands were offering many of the attributes I wanted without ED glass elements. For example, here’s one Fujinon model I considered. If Fujinon of Japan did not consider ED glass as an essential feature in a modern binocular, then why should I?
Consulting former Sky & Telescope columnist, Gary Seronik’s beautifully illustrated book, Binocular Highlights (Second Edition 2017), I was able to affirm what I felt about the view served up by a premium optic compared with mid-priced models:
….You can get good optics for relatively little money. So what do you get if you spend ten times as much? In terms of the actual view, not as much as you might expect. Yes, the more expensive binoculars have better optics that will deliver more light to your eyes and sharper images, but the difference is not night and day. What the extra money does buy is mechanical quality. Expensive binoculars can withstand the inevitable bumps and knocks of everyday use without trouble, and having focusing mechanisms that are sure and precise.
Being new to this type of binocular, I did however find out the hard way that not all roof prism binos were created equal. My first purchase was a model that did have everything I was looking for, save for phase-coating technology which corrects for the inherent design flaw in all roof-prism binoculars. Finally, I purchased a model that did tick all my boxes; enter the Barr & Stroud Sierra 8 x 42.
It’s specifications can be viewed here.
The Sierra 8 x 42 came well packaged inside a handsome box. As well as the binocular, I received a lens cloth, neck strap, soft, padded carry case, a single-page instruction sheet and a warranty card (10 years).
Right from the get-go, I was very impressed with the fit and feel of the binocular. The fern-green body is fashioned from polycarbonate with a rubberised overcoat. The central bridge was set at just the right degree of stiffness, ensuring that when I adjusted the inter-pupillary distance, it was rigid enough to stay snugly in place; so no need for constant re-adjustment when taking them from their case. Both the objective and ocular lenses had good rubber-like caps that can be affixed to the binocular with a much reduced chance of getting lost while on the move.
Both the objective and ocular lenses have lovely anti-reflection coatings that make the lenses all but disappear when looking straight through them.
The Sierra come with adjustable eyecups that click up or down for use with or without eye-glasses. With its generous 17.8mm eye relief, eye-glass wearers will be able to enjoy the full field of view by keeping the eyecups in the fully down position. I do not use eye-glasses when observing, so I always have the eyecups twisted fully upwards.
The diopter setting is located under the right eyecup. It is satisfyingly stiff and, as a result, fairly difficult to adjust. I thought this was plenty good enough for my use, as it has not budged a millimetre since I made the adjustment for my own eyes on the day they were acquired!
As the specifications reveal, the instrument is nitrogen purged and o-ringed sealed making it fog and water-proof. Since molecular nitrogen [consonant with the name ‘azote’, (meaning ‘without activity’) bestowed upon it by early chemists] is quite an inert gas, it also ensures no moisture- or oxygen-induced corrosion will occur to its internal components for the foreseeable future. Argon gas filling would have been better, of course, since it is even more inert (being a Noble element) than nitrogen and its larger atomic mass would ensure even more sluggish diffusion-based leakage over the years. But for my purposes though, ordinary nitrogen was deemed perfectly acceptable. The specs also say the instruments have been immersion tested and can withstand being submerged in up to 1.5 metres of water for 3 minutes; that’s plenty of time to retrieve them if ever an accident should occur!
I’ll not be testing that by the way, lol!
Optical Testing & Handling in the Field
The Sierra 8 x 42 provide instant gratification from the moment you pick it up. It feels very secure in the hand. The view is very clear and sharp and colour rendition sensibly perfect. The factory collimation was spot on. The focus wheel is very responsive and smooth allowing you to zoom in on a subject as close as 6.5 feet all the way out to infinity. If you look carefully at the edges of the field, there is some softening of the image as well as a trace of chromatic aberration but not enough to distract the vast majority of users. Examining a horizontal roof at 30 yards distance revealed very little pincushion distortion.
Comparing it to my old 7 x 50s revealed something rather shocking; the image was actually brighter and sharper in the Sierra, despite it having smaller objective lenses ( 42mm as opposed to 50mm). I attribute this to solid advances in the application of better coatings to all optical components and superior baffling of stray light in the roof prism binocular. Focusing on the middle distance, the binocular provides very impressive depth of field perception but maybe not quite as good as that provided by their porro prism-based counterparts.
Definition of daytime targets is excellent. It presents autumn leaves in their beautiful colours and focusing in on tree trunks showed up its wonderful textured grain. I can easily carry them round my neck for many miles and with little in the way of neck strain. The binocular can also be attached to a tripod if need be using the 1/4-20 threaded socket found under the B&S logo at the front of the bridge. Just unscrew the plastic cover and screw in the tripod adapter.
As a rather severe test of how well stray light is managed in the binocular, I pointed it at the full Moon. The inexpensive 10 x 50s showed clear evidence of internal reflections producing annoying glare in the image and thereby reducing contrast. To my relief, the Sierra 8 x 42 showed very little in comparison indicating that stray light was being very well controlled.
A week after full Moon, I examined a rising last quarter Luna and again, the image was very impressive; there being very little glare and contrast remaining very high. The only false colour I could see was attributed to atmospheric refraction. The battered southern hemisphere with its vast crater fields stood out well, as did the contrast between the brighter and darker maria. I particularly enjoyed seeing the wonderful earthshine from the dark hemisphere of the Moon which made the view all the more magical.
Continuing my adventures with the Sierra under the stars, the binocular has a wide field of view (7.33 degrees), allowing you to take in generous swathes of sky. Stars focused down to tiny pinpoints across the vast majority of the field, with only the edges of the field showing a slight softening and the merest trace of lateral colour. I judged the contrast to be very good.
Confident that I had indeed obtained a very good binocular, I relaxed and just enjoyed the magnificent views it served up of large deep sky objects; the Hydaes was wonderful and filled the view with lots of room to spare, the Alpha Persei Association was spell-binding with many dozens of hot, white stars assaulting my eyes. The Pleiades was a beatufiful sight to behold. Bright stars such as Aldebaran, Capella and Vega faithfully revealed their true colours (orange, yellow and blue-white, respectively).Running the binocular through the Milky Way in Cygnus and Cassiopeia was a joyous experience and proved quite overwhelming to this tester.
The Sierra 8 x 42 will be an excellent new tool in my arsenal of optical instruments. It will complement the detailed, close-up views served up by my telescopes. The binocular will be accompanying us on our up-and-coming family vacation to the Solway Firth in southwest Scotland next week (commencing Monday October 15 2018) together with my 130mm f/5 Newtonian travel ‘scope.
I heartily recommend this binocular to amateur astronomers, nature watchers, for those who love poking around the landscape, or as the perfect optical accompaniment for a day at the races. It will offer up very satisfying performance at a price that won’t break the bank. It provides excellent value for money and, if properly cared for, provide a lifetime of wonderful views.
Please check out some other reviews of Barr & Stroud Binoculars:
Neil English’s new book, Chronicling the Golden Age of Astronomy, explores four centuries of visual telescopic astronomy, as well as the pantheon of colourful characters who helped shape both the hobby and the science today.
It was just over 30 years ago when I was gifted a nice 7 x 50 binocular by my girlfriend. They featured a 7 degree field, multi-coated optics and BaK-4 porro prisms. They served me well all these years on holidays, walks and for casual stargazing. They weren’t cheap either. Lesser units would have fallen apart by now, but after trying a few modern binoculars out I knew that technology had moved on, mostly for the better.
And so had my eyes.
Now that I’m older, I wanted a binocular that had an exit pupil more suited to my age. I wanted an instrument that was more light weight, so that I could observe for longer without using tripods. I wanted a binocular that would do well in a variety of situations, from nature watching from dawn to dusk, and for astronomy. They had to be robust and ideally weatherproof to a degree. My ideal binocular views had to serve up sharp, colour pure views of autumn’s radiant hues but also allow me to throw caution to the wind and just enjoy the glories of the night sky from the comfort of a recliner. But which ones to buy?
Alas, I found that choosing a model that ticked all the boxes for me to be a daunting prospect! Today, we have so many makes to choose from; which is a good thing. My experience with telescopes came in very handy though. Not easily swayed by marketing gimmicks and wishy-washy hyperbole, I slowly pared them down to size.
I decided I wanted a fairly compact, full-size binocular that would offer good light grasp, so a clear aperture of 42mm would be about the minimum that would do the trick. I wanted a fully multi-coated instrument to maximise light transmission to the eye and reduce glare on bright objects to an acceptable minimum. They had to be well made with a decent warranty should they get damaged or worn out from regular use. And they had to present good value for my hard-earned cash.
I narrowed my search down to a good roof-prism binocular as these had many of the features I was looking for; small, light weight, decent light grasp, ultraportable etc. Two magnifications were considered, 8x or 10x. With 10x you’d get a smaller exit pupil and lose some advantages of using them in low light conditions. 10x would also introduce more shake and would be more difficult to accurately focus while in use too, so I decided on 8x; an 8 x 42 binocular.
I went to amazon.co.uk to check out the user reviews of a variety of models I had an interest in. In many ways, these types of reviews give the prospective buyer a more rounded view of what it’s like to use a given model, as they are often more honest and less biased than those offered by so-called ‘experts,’ who, more often than not, succumb to clever marketing ploys and had a tendency to push premium products over more economical models that might still offer perfectly acceptable performance. I found that birders, for example, often highlighted a variety of mechanical and optical features that were largerly superfluous to my needs. I didn’t really need super-fast focusing, locked in dioptre settings, nor ED elements in the objectives. At such low powers, one would be hard pressed to see the advantages of employing low dispersion glass and most of the online literature seemed to over-emphasise their advantages even though I knew that it would only make a small (insignificant?) difference to the views. Afterall, how many amateur astronomers insist on having ED finder ‘scopes eh? Why haven’t 8 x 50 ED finders or some such become the industry standard, if they really offered any tangible advantage over good ole crown & flint? The honest answer is that they’re unnecessary, and so can be dispensed with.
As a case in point, check out this user review of the Vortex 10 x 42 Diamondback roof prism binocular. The gentleman states that he was asked to try out the more expensive Viper model with ED objective elements in a blind test. He states that he couldn’t really tell the difference in field use. I have no reason to doubt the gentleman’s conviction. Why lie on such a trivial matter?
No, a good, no-frills, traditional achromatic binocular to match my average eyes was what I was shopping for!
I went with a company that had a long track record of producing high quality optics, as I reasoned that such knowledge would be invaluable in the construction of a well-made binocular. Many companies selling such binoculars were not long in the game though, so my instinct was to avoid them. I gravitated toward an old British firm that had produced optics for the military in two world wars; Barr & Stroud.
Now bought out by OVL, Barr & Stroud re-entered the sports optics market by bringing out a range of affordable roof prism binoculars in an 8 x 42 format and my first purchase was the Sahara 8 x 42, which retails for about £70-£90 UK.
Though under no illusions that these are British made, Barr & Stroud binoculars are now assembled in China, just like those marketed by Vortex (a US-based company) and many other companies. They are supplied with a nice, soft carry case, neck straps, a lens cleaning cloth and have a 10-year warranty.
The specifications of the Sahara 8 x 42 model can be viewed here.
The Sahara is a joy to use. It’s small and light weight (670g), has good eye relief (17.5 mm) and with its twist up eyecups, will allow those who must wear eye glasses (I don’t) to enjoy the expansive field of view (7.33 angular degrees). Images are bright and sharp and colour fidelity is sound. With its fully multi-coated optics, contrast and glare suppression are excellent too in comparison to my old 7 x 50s. You really have to look for chromatic aberration but it is there. You can best see it by focusing on the edge of a telephone pole against a bright, overcast sky background, but is minimal and not in the least bit intrusive(I’d say mostly bum-fluff). At the edge of the field, the image gets a little softer with some slight fringing during daylight hours but it will never be enough to disturb the vast majority of users. Focusing is smooth and intuitive, not overly stiff or loose and it has an excellent close focus distance of just under 2m (measured) to allow you to enjoy insects, flowers etc at close range. It also has adequate waterproofing for my intended uses for it.
Night time views were very impressive too. Stars are sharp and pinpoint across the majority of the field. Only by using a stable tripod, will you be able to notice a little defocus of the stellar images at the edge of the field. All in, I would rate the Sahara as very good and considering its modest cost; a great bargain in today’s market! These guys certainly know how to make a good binocular!
Shortly after purchasing the Saharas, I began researching the properties of roof prisms and discovered that they have a significant design flaw. In the roof prism design, the two halves of the collected light from the objectives travel through the prism independently and are recombined before reaching the eyepieces. Because the path of the two wave trains are of slightly different lengths, one half of the light takes a little longer to travel through the prism than the other. When the two halves of the image are recombined, the wave with the longer light path will be slightly out of phase with the light that undergoes the shorter route. This results in a combination of destructive and constructive interference of the wave trains, affecting the colour balance, contrast and fidelity of the binocular image.
Note that this flaw does not affect porro-prism-based binoculars!
By introducing a special phase coating to the prism undergoing the shorter light path, optical designers can slightly retard the wave train, thereby correcting the phase difference with the other wave train. This results in sharper, brighter images with higher contrast; in theory. As I researched this some more, I discovered that the result was quantitatively significant; 8 per cent according to the manufacturers. Intrigued, I looked for a Barr & Stroud model that had this phase coating as the Sahara’s did not have this technology built in and that quickly led me to their 8 x 42 Sierra model.
Luckily, the Sierra was only a little bit more expensive than the Sahara. Full specs here.
Otherwise sharing very similar specifications to the Sahara, the Sierra 8 x 42 is also slightly lighter (650g), coming with the same soft carry case and accessories as the former. The polycarbonate body was also a little different in the Sierra compared with the Sahara, as the above images show. When it arrived, the first thing I did was undergo a test to see if there was any significant difference between the images. Examining a brightly lit scene with a trunk of a tree shadowed by some over-hanging branches and comparing the two binocular images, I must admit that the Sierra was that little bit better. It’s difficult to describe in words but I suppose I’d say that the Sierra image had a little bit more ‘zing’ to it. The image was that little bit brighter and the colours more vivid. Contrast was also better by a shade.
Based on this test, I think phase coating technology is definitely worth having. Subsequent research of other high-end and mid-priced binoculars revealed that they all possessed these phase coatings. I see them as increasing the overall efficiency of light transmission, improving the image in a way that the human eye would notice in a critical test.
In another test comparing my 7 x 50s to the Sierra’s, I had to immediately concede that the images in the latter were far superior to the old porro prism binocular. The image was actually brighter even though it only had 42mm objectives(as opposed to 50mm in the auld yin) and the contrast far superior. The Sierra also presented a larger field of view.
Man and his technology!
Before describing my experiences with the Sierra 8 x 42 in any more detail, I was curious to see how the unit would fare compared with a high-end binocular with roughly the same specifications. As luck would have it, my coalman is a keen birder and dabbles in hunting big game. He’s the proud possessor of a Swarovksi EL 8.5 x 42 binocular, which retails for about £1800 UK. When he came to deliver some coal I got chatting with him and asked him if he would be so kind as to bring them by some afternoon so that we could compare and contrast the images garnered by these binoculars. He agreed.
Though certainly not a ‘gayponaut’ (a word of my own coining, fomally defined as: an irrational obsession with small ED optics), my coalman, Graham, bought his Swarovski’s about ten years ago, and I was glad to see that they looked as though they’d been used. When I asked him why he chose them he said, “they’re supposed to give brighter views in low light.” I thought that answer was a little vague though. He didn’t seem to know anything about the fluorite element in the objectives, or the effects of coatings on the optics. He was simply won over by the advertising. I believe this is common among buyers of high-end optics. Afterall, you don’t need to know anything about an internal combustion engine in order to drive a car do you?
Indeed, I knew far more about his Swarovski’s than he did. Nevertheless, we compared the images. I got a shot of Graham’s 8.5 x 42s and he got a chance to test out my 8 x 42 Sierra’s. The results were interesting.
I felt the image quality was excellent in the Swarovski’s. It gave a slightly more neutral colour tone to the Sierra’s in a very slightly larger true field (7.6 angular degrees). Contrast was excellent with really first-rate definition. The built-in field flattening lenses in the eyepieces improved the edge of field correction, and the slight colour fringing I had tried hard to detect in my Sierras was invisible in the Swarovski’s.
Graham liked the Sierras too though. Indeed, he said to me that, ” they’re pretty much the same aren’t they?”
I found it hard not to disagree. I felt the images were much more similar than different.
But what I did appreciate were the mechanical attributes of Graham’s binocular. Its buttery smooth focusing wheel made it easy to adjust focus distance from about 4.5 feet to infinity very swiftly; a bonus for birders I guess. I also appreciated the wonderful diopter adjustment apparatus and hearing the ‘click’ as it was turned to the correct setting. This clever diopter locking mechanism means that there’s little chance of it slipping out of place during field use. Great, but not something I couldn’t live without.
The Swarovski’s body is a very rugged magnesium alloy chassis which gives a feeling of reassurance while handling the optic, but I didn’t really understand how it would be more resistant to corrosion over the far less expensive polycarbonate body usually found on the majority of sports optics. What Graham and I did notice was the significant weight difference between the models. The Swarovski’s were nearly 200g heavier than the Sierra’s, something that would definitely have a bearing on observing comfort during prolonged field use.
The excellent life-time warranty on the Swarovski’s was something Graham appreciated. He told me that one of the caps on the ocular lens had worn out (they can actually be removed for easy cleaning of the eye lenses) but one of the company reps immediately fitted his unit with a new one; that’s great service!
In the end, I was very grateful to Graham for bringing by his high-end binocular. I was delighted to know that there wasn’t much in it optically. But then again, I kind of expected as much! Did the experience tempt me to save and invest in a Swarovski? I’d have to say no. My Sierra’s were plenty good enough, warts and all!
What to do with the Sahara’s? My sister- and brother-in-law love the great outdoors; camping, glamping, fly fishing, hill walking and sight seeing. The’ve never owned a decent binocular so these will serve as a suitable Christmas gift for them. I just know they’ll love it and use it!
As for the Barr & Stroud Sierra binocular, I will present a separate, in depth review of this instrument in another blog.
Thanks for reading!
Neil English is author of several books on amateur astronomy.
As I discussed at length in previous blogs, my chosen grab ‘n’ go telescope of choice is a high performance Newtonian reflector with an aperture of 130mm (5.1 inches) and focal length of 650mm (f/5). The telescope has an excellent Skywatcher primary mirror, the original secondary mirror was replaced by a higher quality unit with a slightly smaller semi-major diameter of 35mm, yielding a very modest central obstruction of just 26.9 per cent. Both mirrors received new, state-of-the-art ultra-high reflectivity coatings to increase both light throughput and image contrast. The interior of the tube is lined with cork and covered with matt-black flocking material to minimise stray light and more effectively deal with thermals. Best of all, the entire outlay was very economical, setting me back just a couple of hundred pounds.
In field tests, the instrument, once collimated and acclimated completely outclassed more traditional grab ‘n’ go telescopes, including a high-quality 90mm apochromatic refractor on lunar and planetary targets, double stars and a veritable pantheon of deep sky objects. In a series of more recent tests, it was shown to give better daylight images than a 5″ f/12 classical refractor and closely approached its light gathering power and resolution on a variety of nighttime targets.
The instrument is very light weight and completely stable on a sturdy Vixen Porta II alt-azimuth mount equipped with slow motion controls. The instrument is very easy to collimate using either a Chesire eyepiece or laser collimator and perfect results can be achieved in a matter of seconds. Its low mass ensures that it acclimates very quickly to ambient, allowing me to engage with celestial targets very quickly. For low and medium power views (up to 80x or thereabouts), the telescope can be used more or less immediately. For higher resolution targets, it’s fully equalised in about 30 minutes, even on the coldest nights. Tucked away in its lightweight aluminium carry case, it has travelled to many destinations in the British Isles where its excellent optics has enabled it to perform flawlessly.
As I explained earlier, I do as much daytime observing as I do at night and in this capacity, the telescope has thrilled its owner with crisp, high resolution details of the Creation, especially at powers in excess of 100x, where traditional spotting ‘scopes with their smaller apertures, rapidly run out of light. This is all well and good but Newtonian reflectors produce images that are both up-side down and right-left reversed, making traditional kinds of nature spotting problematical. Try observing a distant ship at sea using a Newtonian to see what I mean. These limitations led me on a quest to acquire and test a variety of products that promised to remedy this problem.
Product 1: SkyWatcher 10mm Erecting Eyepiece
Costing about £25 plus shipping, the unit also comes with an extension tube, which was not found to be necessary. It works by using an internal roof prism sandwiched between the field lens and eye lens. The eye lens is anti-reflection coated but its field lens is not. Examining the roof prism also indicated that it was not coated.
The consequences of not coating all the optical components, even if perfectly executed are three fold; first contrast will be diminished, secondly, it will cause ghost images when observing bright objects. Finally, it will lose light producing images that are a fraction dimmer than conventional eyepieces with good coatings.
Optically, it delivers a power of 65x and the image is reasonably good and sharp, with a nice, hard field stop. It is very small and lightweight but it lacks the punch of a regular eyepiece that possess either fully coated or multicoated lenses and performs poorly when imaging bright daylight objects such as water reflections etc. Examining the bright planet Venus one evening, the eyepiece revealed prominent ghosting in the image which I found distracting. If you are looking for the best images from daylight tests, this is not a product I would recommend.
Product 2: Roof-prism based image rectifiers
Two such devices were purchased; one unit called “Angeleyes” and the other marketed by “Datyson”. Both devices enable one to use eyepieces interchangeably and cost about £30 plus shipping.
Both are 4.5 inches long, with only the upper bodies protruding above the focuser. Both have a multicoated Barlow lens placed ahead of an internal roof prism. The selected eyepiece is mounted inside the upper body and secured with a single screw.
In what I consider to be rather nefarious marketing, one of the units was advertised as delivering a 1.5x amplification, while the other stated that the Barlow delivered 2x. In fact though, both products were identical apart from their labelling. Worse still, the amplifaction was more like 3x on both units. Examining the internal roof prisms showed that they were uncoated.
All eyepieces tested came to focus with these units. The lowest power oculars tested; a 32mm Plossl and 26mm Celestron X-Cel produced images that were quite good, but in order to see the full field of view your eye must be placed about an inch above the eyelens. In other words, the eye relief with these units is huge! This was not found to be an issue in and of itself, and indeed made the experience very relaxing. Still, they did not deliver the low power views that I was enjoying using these eyepieces on their own; they amplified the image too much. Instead of having a low power of 20x and 26x respectively, these units were giving images of the order of 60x; not low enough to enjoy wider fields of view during daylight hours.
Testing these units with higher power eyepieces showed that they produced far too high magnifying powers that were not as sharp as the equivalent eyepiece at the same effective focal length. This was confirmed in nightime tests, where one of the units did not resolve Epsilon 1 & 2 Lyrae as well as a normal high power eyepiece. Image sharpness was definitely compromised.
Though certaiinly useful, I would not recommend either of these units to those looking for the best daylight performance from a small Newtonian telescope.
Product 3: The Vixen Terrestrial Image Adapter
The Vixen terrestrial adapter was purchased from an authorized Vixen dealer within the UK. Costing £80 delivered, the unit is a three lens system and does not employ roof prisms. The product is very well engineered and executed in a quality, all-metal body. It has a modular design, with three sections that thread into each other. It was fun taking it apart. Examining all the lenses on either side of the various segments showed clear blooming. The lenses are all anti-reflection coated. The device is about seven inches long.
Like the previously discussed units, the Vixen adapter allows one to insert any eyepiece into the upper stage. But unlike the fomer, there is no amplification of the image, so the magnification you get from the native eyepiece is preserved using this device. Only 1.25″ eyepieces can be used with this unit.
Testing the device out on daylight targets, the Vixen unit delivered crisp, clear images across a field that maxes out at ~1.5 angular degrees. Since my preferred low power eyepiece for the 130mm f/5 Newtonian is a 25mm Celestron X-Cel LX ( 26x), this results in a reduction in the true field available to the native eyepiece but it was still wide enough to satisfy this tester.
Like the prism-based image rectifiers, the Vixen unit has very large eye relief, with the result that you have to move your eye above the top of the low power eyepiece to see the full field. I found this arrangement to be very comfortable.
The Vixen unit produced excellent images with higher power eyepieces, including an 11mm ES 82, a Park Gold 7.5mm, a 4.8mm T1 Nagler and a 2.3mm Celestron X-Cel LX, delivering powers between 59x and 283x.The shorter the focal length of the eyepiece, the closer one has to place one’s eye above the eye lens. Comparing the views with the eyepieces used alone, there was very little light loss, with image sharpness and contrast remaining very high.
Switching to nightime use, examination of a bright waning gibbous Moon with the Vixen unit produced very satisfactory results. The lunar regolith was razor sharp at all magnifications between 26x and 283x and I could also confirm that the maximum true field delivered was 3 full Moon diameters, or about 1.5 angular degrees, as previously estimated. A brief test on Epsilon 1&2 Lyrae with the 2.3mm Celestron X-Cel LX ocular delivered much sharper images of the four components. Optical quality is clearly superior to the roof prism-based units previously described.
Based on these tests, I am very happy to recommend the Vixen terrestrial adapter to prospective buyers, as it will deliver very good, clean images of daylight targets in their natural orientation. That Vixen has developed and brought this product to market suggests that there is some demand for terrestrial viewing using small Newtonians. Why create such a high quality product if there is no demand for it?
Notes on field use:
Being accustomed to using the slow motion controls on the Vixen Porta II mount using eyepieces that naturally invert the image in Newtonian mode, it takes quite a bit of getting used to learning how to accurately manoeuvre the telescope using the same slow motion controls when viewing in terrestrial mode. This comes with the territory. Like everything else, practice makes perfect! Though the adapter looks awkward, it is very easy and comfortable to use. Close focus distance is ~ 20-25 yards.
Independent verification of these findings
I found one online review of the Vixen terrestrial adapter, which affirms the general findings of this tester;
Tried it tonight on the Moon. I thought it performed quite well. It made no major differences to the views through my 32mm and 20mm TV plossls. The image was exactly the orientation I see by naked eye and binoculars – just what I wanted! It was funny, however, moving the scope. I have trained myself well, so I kept heading the wrong direction :lol:. But I got the hang of it. Next to try it on a starhopping exercise. I’ll wait for dark skies.
Comparison with conventional spotting telescopes
Preamble: Please consider this review of the Celestron 100mm aperture ED spotting scope. The reader is encouraged to consider its specfications, including weight, complexity of the design, magnification range, colour correction, twilight factor, field of view, close focus distance and cost. The reader will note that this is one of the more economical models on the market; the equivalent premium products are much more expensive.
Let’s compare the specs for a 130mm f/5 Newtonian and the Celestron 100ED spotter
Aperture 130mm 100mm
Resolving power 0.89″ 1.14″
Colour correction Fully apochromatic Pseudo apochromatic
Twilight factor 58 46.9
Field of view (max) 1.5 degrees 1.9 degrees
Magnification range 26-300+ 22-67x
Close focus distance 20-25 yards 25 yards
Length 23.5″ 20″
Weight: 3.8 kg 2.52kg
Cost: ~£350 £1,180
Interchangeable eyepiece yes no
You can see at a glance that the Newtonian will offer brighter, higher resolution images at high magnifications than the ED spotter. It’s not rocket science. Think pixels. The 130mm has more ‘pixels’ than the 100mm ED spotting ‘scope. The Newtonian will also work considerably better in low light conditions (better twilight factor) compared with the refractor. I especially appreciate this during the very short days of winter, where light is often at a premium here at 56 degrees north latitude. It was very noticeable last winter when I was conducting tests comparing a 90mm ED refractor and the130mm Newtonian.
The spotting ‘scope is more rugged than the Newtonian but that’s because it must be by necessity; it has to protect all of the components that make it work well. No such fussing is needed with the Newtonian, which can be knocked about and whipped into perfect collimation as and when required .It’s the ultimate low-stress ‘scope! Best of all, the price differential is huge. I’ll leave it up to the reader to decide if the 100mm ED spotter represents genuine value for money, but I can say with certainty that the Newtonian most definitely is.
Having said all of this, for many objects I view during the day, an erecting adapter is quite unnecessary and when I don’t need to use one, I don’t. For night use, the Vixen terrestrial adapter sits pretty in its box. I’m happy with a topsy turvy cosmos lol.
Moral of story: Improvements are costly!
Neil English explores the history of four centuries of visual telescopic astronomy in his new book; Chronicling the Golden Age of Astronomy.
This is an excellent book and will complement Ashbrook’s Astronomical Scrapbook and therefore have wide appeal to both amateur and professional astronomers.
Wayne Orchiston, Professor of Astrophysics, University of Southern Queensland, Australia.
Introduction & Acknowledgements
Achievements of the Classical Refractor: A Timeline
Thankyou for waiting!
*** New testimonies recently added to the end of the article.
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.
Ed Moreno, 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?
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, due out in October/November 2018.
but test everything; hold fast what is good.
1 Thessalonians 5:21
Introduction: One of the statements that is oft quoted by observers, particularly in the UK, is that the meteorological phenomenon known as the Jet Stream seriously affects the quality of high resolution telescopic targets. I have decided to investigate these claims to determine to what extent they are true or not, as the case may be. These data will also provide the reader with an idea of the frequency of nights that are available for this kind of testing over the time period the study is to be conducted.
Method: For simplicity, I shall confine my studies to just four double stars that have long been considered reasonably tricky targets for telescopists. To begin with, my targets will include systems of varying difficulty, ranging from 2.5″ to 1.5″ separation, and the aim is to establish whether or not I can resolve the components at high magnification. These systems include *:
Epsilon 1 & 2 Lyrae
* These systems were chosen for their easy location in my current skies, but may be subject to change as the season(s) progress.
Viewers are warmy welcomed to conduct their own set of observations to compare and contrast results in due course.
Instrument Choice & Magnifications Employed:
A high-performance 130mm (5.1″) f/5 Newtonian reflector was employed to investigate the effects of this phenomenon, as this is an aperture regularly quoted as being sensitive to the vagaries of the atmosphere. Magnifications employed were 260x or 354x (they can however be resolved with less power). The instrument at all times was adequately acclimated to ambient temperatures and care was taken to ensure good collimation of the optical train. No cooling fans used on any of my instruments.
Date: August 17 2018
Time: 21:20 to 21:35 UT
Location of Jet Stream: Currently over Scotland
Conditions: Mild, 14C, very breezy, mostly cloudy with occasional clear spells, frequent light drizzle.
Observations: Power employed at the telescope 354x
Epsilon 1 & 2 Lyrae: all four components cleanly resolved.
Delta Cygni: Faint companion clearly observed during calmer moments
Epsilon Bootis: Both components clearly resolved during calmer moments.
Pi Aquilae: Slightly mushier view, but both components resolved momentarily during calmer spells.
Date: August 19 2018
Time: 20:30 – 21:50 UT
Location of Jet Stream: Currently over Scotland.
Conditions: Mild, 13C, mostly cloudy and damp all day but a clear spell occurred during the times stated above, no wind, heavy dew at end of vigil.
Observations: Seeing excellent this evening (Antoniadi I-II); textbook perfect images of all four test systems at 354x and 260x.
Nota bene: A 12″ f/5 Newtonian was also fielded to test collimation techniques and I was greeted with a magnificent split of Lambda Cygni (0.94″) at 663X. Little in the way of turbulence experienced even at these ultra-high powers. Did not test this system on the 130mm f/5.
Clouded up again shortly before 11pm local time, when the vigil was ended.
Date: August 22 2018
Time: 23:30-40 UT
Location of Jet Stream: Currently over Scotland
Conditions: Very mild (15C), breezy, predominantly cloudy with some heavy rain showers interspersed by some brief, patchy clearings.
Observations: Just two test systems examined tonight owing to extremely limited accessibility; Epsilon 1 & 2 Lyrae and Delta Cygni. Both resolved well at 260x.
Date: August 22 2018
Location of Jet Stream: Currently over Scotland
Conditions; partially cloudy, brisk southwesterly wind, bright Gibbous Moon culminating in the south, +10C, rather cool, transparency poor away from zenith.
Observations: The telescope was uncapped and aimed straight into the prevailing SW wind, as is my custom.
All four systems well resolved at 354x, although visibility of Pi Aql was poor owing to thin cloud covering.
Date: August 23 2018
Time: 20:30-45 UT
Location of Jet Stream: Moved well south of Scotland
Conditions: Mostly clear this evening, after enduring heavy showers all day; cool, 10C, fresh westerly breeze, good transparency.
Observations: All four test systems beautifully resolved this evening (seeing Ant II) at 354x. Just slightly more turbulent than the excellent night of August 19 last.
Date: August 24 2018
Time: 20:30-45 UT
Location of Jet Stream: Just west of my observing site.
Conditions: Almost a carbon copy of last night, light westerly winds, cool (9C), good transparency and almost no cloud cover. Very low full Moon in south-southeast.
Observations: All four system resolved at 260x, but less well at 354x owing to slightly deteriorated seeing ( II-III). Delta Cygni seems especially sensitive to seeing.
Nota bene: Epsilon Bootis now sinking fast into the western sky. This test system will soon be replaced by a tougher target, located higher up in my skies; Mu Cygni.
Date: August 25 2018
Time: 20:20-21:00 UT
Location of Jet Stream: Right over Scotland.
Conditions: Very hazy, calm, poor transparency, cool (9C), seeing excellent (I-II)
Observations: Just three of the four systems examined tonight owing to very poor transparency. Only Pi Aquilae could not be examined. All three were beautifully resolved at 354x.
Date: August 26 2018
Time: 22:30-23:05 UT
Location of Jet Stream: Well south of Scotland.
Conditions: After a day of heavy rain, the skies cleared partially around 11pm local time. Fresh westerly breeze, fairly mild (12C), bright full Moon low in the south.
Observations: Mu Cygni observed instead of Epsilon Bootis owing to the latter’s sinking low into the western sky at the rather late time the observations were made.
Three systems well resolved ( Mu Cygni, Pi Aquliae and Epsilon 1 & 2 Lyrae) in only fair seeing, with Delta Cygni B only spotted sporadically in moments of better seeing. This system is very sensitive to atmospheric turbulence due to a large magnitude difference between components, as opposed to their angular separation. 260x used throughout.
Nota bene: Readers will take note of the frequency of observations thus far made.
Date: August 27 2018
Time: 20:30-21:05 UT
Location of Jet Stream: West of the Scottish mainland.
Conditions: Mostly cloudy, mild, 13C, light westerly breeze.
Observations: I took advantage of a few brief clear spells this evening to target my systems(including Epsilon Bootis). Seeing very good despite the cloud cover (II). All four systems easily resolved tonight at both 354x and 260x.
Date: August 29 2018
Location of Jet Stream: Not over Scotland.
Conditions: Mostly clear, occasional light shower, cool (11C), light westerly breeze, seeing and transparencyvery good (II).
Observations: Mu Cygni now replaces Epsilon Bootis.
All systems very cleanly resolved at 354x and 260x.
Nb. All systems also beautifully resolved in a 12″ f/5 Newtonian at 277x, set up alongside the 130mm f/5.
Date: August 30 2018
Time: 20:45- 21:00 UT
Location of the Jet Stream: Not over Scotland.
Conditions: Partially cloudy with some good clear spells, cool (9C), very little breeze.
Observations: Seeing good tonight (II). All four systems nicely resolved at 260x and 354x.
Note added in proof: Local seeing deteriorated (III-IV) somewhat between 21:00 and 22:00 UT, so much so that Delta Cygni B could no longer be seen.
Date: 31 August 2018
Location of Jet Stream: North of the British Isles
Conditions: Partly cloudy and becoming progressively more hazy as the vigil progressed. Mild, 12C, very light westerly breeze.
Observations: Seeing only fair this evning (II-III), all four systems resolved at 260x and 354x, though Delta Cygni B visibility was variable.
Date: September 1 2018
Location of Jet Stream: to the northwest of the Scottish Mainland.
Conditions: Partially clear, very mild (16C), light southerly breeze, good transparency.
Observations: Seeing quite good (II). All four systems resolved at 260x and even better delineated at 354x under these clement conditions.
Date: September 4 2018
Location of Jet Stream: Not over Scotland.
Conditions: Cool (10C), mostly clear, light westerly breeze, good transparency.
Observations: Seeing very good (II). All four test systems well resolved at 260x and 354x this evening.
Date: September 5 2018
Location of Jet Stream: Not over Scotland.
Conditions: Very unsettled with frequent squally rain showers driven in by fresh westerly winds. Good clear spells appearing between showers. Transparency very good. 12C
Observations: All four test systems resolved under good seeing conditions (II) at 260x and 354x.
Date: September 6 2018
Time: 20:00-25 UT
Location of Jet Stream: Not over Scotland.
Conditions: Cool (8C), little in the way of a breeze, mostly clear, excellent transparency.
Observations: Seeing good (II). All four test systems well resolved at 260x and 354x.
Date: September 7 2018
Location of Jet Stream: Not over Scotland.
Conditions: A capital evening in the glen; 11C, good clear sky, brisk westerly breeze, excellent transparency.
Observations: Seeing very good (I-II). All four test systems beautifully resolved in the 130mm f/5 using powers of 260x and 354x
Know thine history!
Any serious student of the history of astronomy will likely be acquainted with the early work of Sir William Herschel (Bath, southwest England), who employed extremely high powers (up to 2000x) productively in his fine 6.3-inch Newtonian reflector with its speculum metal mirrors. The high powers employed by this author are thus fairly modest in comparison to those used by his great predecessor. Check out the author’s new book; Chronicling the Golden Age of Astronomy, due out in October/November 2018, for more details.
Note added in proof:
With the excellent conditions maintained well after midnight, I ventured out at about 00:00 UT, September 8, and noted Andromeda had attained a decent altitude in the eastern sky. At 00:10UT I trained the 130mm f/5 Newtonian on 36 Andromedae for the first time this season and charged the instrument with a power of 406x. Carefully focusing, I was treated to a textbook-perfect split of the 6th magnitude Dawes classic pair that are ~1.0″ apart. It was very easy on this clement night. The pair look decidely yellow in the little Newtonian reflector. I made a sketch of their orientation relative to the drift of the field; shown below.
If you have a well collimated 130P kicking about why not give this system a try over the coming weeks?
Date: September 9 2018
Location of Jet Stream: Currently over Scotland
Conditions: Frequent heavy showers driven in from the Atlantic with strong gusts, 11C, some intermittent clear spells.
Observations: Seeing III. 3 systems fairly well resolved this evening. Delta Cygni B only seen intermittently. Magnification held at 260x owing to blustery conditions.
Date: September 12 2018
Location of Jet Stream: Currently over Scotland
Conditions: Very wet, windy with some sporadic clear spells, good transparency once the clouds move out of the way. 10C.
Observations: Seeing (II-III). Just three systems examined tonight; the exception being Pi Aquliae, which was not in a suitable position to observe. All three were well resolved at 260x. Did not attempt 354x owing to prevailing blustery conditions.
Date: September 12 2018
Time: 21:40-55 UT
Location of Jet Stream: Not over Scotland
Conditions: Still unsettled, blustery light drizzle and mostly cloudy with some clear spells. 10C.
Observations: Seeing (III), three systems resolved well, Delta Cygni B not seen cleanly at 260x under these conditions.
Date: September 14 2018
Location of Jet Stream: Currently over Scotland.
Conditions: Rather cool, (9C), very little breeze, rain cleared to give a calm, clear sky.
Observations: Seeing II. All four systems cleanly resolved at 260x and 354x
Date: September 16 2018
Location of Jet Stream: Currently over Scotland
Conditions: Mild (12C), fresh south-westerly breeze, some occasional clear spells.
Observations: Seeing very good (II), all four systems cleanly resolved at 260x and 354x.
Overall Results & Conclusions:
This study was conducted over the course of one month, from mid-August to mid-September 2018, a period covering 31 days.
The number of days where observations could be conducted was 21, or ~68% of the available nights.
No link was found between the presence of the Jet Stream and the inability to resolve four double star systems with angular separations ranging from ~2.5-1.5″. Indeed, many good nights of seeing were reported whilst the Jet Stream was over my observing location. In contrast, some of the worst conditions of seeing occurred on evenings when the Jet Stream was not situated over my observing site.
There is, however, a very strong correlation between the number of nights available for these observations and the efforts of the observer.
Many of the nights the Jet Stream was located over my observing site were windy, but this was not found to affect seeing. While the wind certainly makes observations more challenging, it is not an indicator of astronomical seeing per se. That said, no east or northeast airflows were experienced during the spell these observations were conducted. At my observing site, such airflows often bring poor seeing.
The archived data (from January 16 2014) on the Jet Sream site linked to above provide many more data points which affirm the above conclusions.
I have no reason to believe that my site is especially favoured to conduct such observations. What occurred here must be generally true at many other locations.
These results are wholly consistent with the available archives from keen observers observing from the UK in the historical past. This author knows of at least two (or possibly three) historically significant visual observers who enjoyed and documented a very high frequency of suitable observing evenings in the UK.
Contemporary observers are best advised to take Jet Stream data with a pinch of salt. It ought not deter a determined individual to carry out astronomical obervations. Perpetuating such myths does the hobby no good.
Neil English debunks many more observing myths using historical data in his new book, Chronicling the Golden Age of Astronomy, due out in October 2018.
Introduction: Many telescope reviews conducted on forums or in magazines only assess a single instrument, namely the one under consideration, entirely on its own terms. But while such informaton can be useful, particularly if a fault is discovered, it can be somewhat misleading if no other instruments are compared with it. Take for example, a top drawer 60mm refractor, which produces excellent images within the remit of its aperture, but when it’s compared to a slightly larger telescope of average quality, it begins to show its limitations and the tester gains a much more balanced view of its strengths and weaknesses.
I find myself thinking this way when evlauating all the telescopes that pass through these parts. Such tests are very important and completely warranted. For example, I was once very much enamoured by an expensive 4-inch F/5 Televue Genesis fluorite refractor but quickly fell out of love with it once I compared it to an even more expensive Televue 102 apochromat. In turn, the latter telescope was found to be slightly inferior to a SkyWatcher ED 100 f/9 refractor costing far less than either of the Televue refractors, which left a very bad taste in my mouth, making me deeply suspicious of the claims proferred by those who market so-called ‘premium’ telescopes, as well as the forum fanboys who apparently cannot see beyond them.
But sometimes it pays dividends to compare good telescopes from different genres too, such as my discovery that an 8-inch f/6 Dobsonian proved superior to a 7-inch f/15 Maksutov Cassegrain, even though the former was less expensive. Clearly, you don’t always get what you pay for! You need to find the truth for yourself.
In this capacity, I decided to compare and contrast the capabilities of two very different telescopes of similar aperture; a 127mm f/12 achromatic refractor and a 130mm f/5 Newtonian reflector costing many times less. I have described the capabilities of this refractor in many previous blogs (now archived by the author). I have retained it as an excellent example of a historically important class of telescope that allowed amateur and professional astronomers to make great strides in understanding the Universe around them and which continues to provide excellent insights into their considerable capabilities. Interested readers will find a veritable treasure trove of classical achromat ‘culture’ in the author’s up-and-coming book, Chronicling the Golden Age of Astronomy, due out in late 2018.
But having said all of this, the Newtonian reflector has been terribly neglected by a generation of amateurs that seem to know the price of everything and the value of nothing. Unwilling to take their cue from the professional community, who have long left the refracting telescope behind in favour of the enormous advantages offered by modern reflective optics, they continue to disseminate misleading or downright false information to unsuspecting newcomers to the hobby, who are subsequently led astray in such a way that their progress as observers becomes severely stunted. That’s why it’s important to continue to question received opinion. If we stop questioning, we quickly become part of the herd culture that so typifies contemperary amateur astronomy.
The instruments compared: The refracting telescope is a high-quality neo-classical instrument (doublet objective) with an aperture of 127mm and focal length of 1524mm (so f/12). The optical tube assembly is about 1.8m long and weighs in at 40 pounds. It sports a fully multi-coated object glass which passes virtually all the light that passes through it. It has a state-of-the art, dual speed Moonlite focuser, which is fully rotatable and extremely robust.
Such a bulky instrument requires a substantial mount and even when provision is made for its mounting (with its various counterweights) it can prove very awkward to use in the field, particularly when the instrument is pointed high in the sky.
The Newtonian, in contrast, even with its dovetail plate and finder attached, is featherweight in comparison. Both primary and secondary mirrors possess quality, high-reflectvity coatings, reflecting 97 of the light incident upon them and with a small 27 per cent central obstruction with its upgraded optical flat, it loses very little light to deliver tack-sharp, colour free images with high contrast. It’s focuser, however, is of the simple, single speed, rack & pinion variety. It needs to be accurately collimated for such testing but this requires just a minute of one’s time to attain perfect results.
Test 1: Comparison of the high magnification images in daylight; conducted August 21 2018.
Both telescopes were set up on their mounts (the reflector was mounted on a simple Vixen Porta II alt-azimuth) during a warm, overcast day and the instruments charged with a high magnification (~ 50x per inch). The refractor delivered a power of 277x, while the reflector yielded a magnification of 283x. Both telescopes were aimed at the topmost bough of a horsechestnut tree some 80 yards distant and the instruments carefully focused.
Results: Both instruments served up sharp, detailed images of the well-developed foliage. The Newtonian was much harder to focus accurately owing to its fast f ratio(5), in comparison to the refractor (f/12). They were very comparable in terms of image brightness but the reflector showed a consistently better image. It was a shade sharper and completely devoid of chromatic aberration (CA). The refractor did show some CA in comparison, which manifested a faint chromatic fog, lowering image contrast and sharpness.
I called two other visual testers to the telescope; my wife and my my next-door neighbour, Trevor. Teaching them how to focus the telescopes finely, I let them examine the images in both telescopes for a few minutes, eventually enquiring of them which instrument delivered the better high power daylight views.
Their verdict was the same as my own, namely, that the reflector delivered the better image of the tree-top foliage.
Comments: It might have been anticipated that the refractor would offer the brighter image, but CA takes some of the unfocused light and spreads it around the field, slightly lowering the overall brightness of the focused image.
Test 2: Double Star Performance: August 22 2018
Wide field performance tests aborted until the Moon was out of the sky. Some double stars were critically examined instead.
Conditions: Brisk southwesterly winds, partially clear, visibility rather poor except near zenith. Temperature + 10C, rather cooler than of late.
Both telescopes were set out to cool from the late evening (19:00 UT) onwards, so completely acclimated to their environments.
4 systems examined at high powers (260x and 277x on the 130mm f/5 and 127mm f/12, respectively):
Epsilon Lyrae 1 & 2
Results: Only a brief observing spell possible with by telescopes this evening between 21:00 and 21:25UT as low cloud moved in and made the sky increasingly difficult to navigate. By 22:00 it had all but competely clouded over again.
Both telescopes resolved all four systems well at the powers mentioned above. The breezy conditions and the high altitude of three of the test systems made it very challenging to observe in the refractor owing to its long tube and positioning of the eyepiece very near the ground (a Televue 2-inch EverBrite dielectric diagonal being employed to make observations easier). The same systems proved far more comfortable to observe in the Newtonian, for obvious reasons. The long refractor really needs a massive equatorial mount to do it justice; something I am not interested in pursuing.
The refractor definitely pulled ahead though in terms of ease of focus of the subjects (at f/12 you’d expect that), while using the reflector with its simple rack & pinion focus and f/5 relative aperture was always much more challenging. Indeed, I had forgotten the considerable advantages the classical refractor has over faster systems in this regard. The refractor images showed little in the way of diffraction artifacts, the stellar Airy disks being very tight and round as buttons. Contrast was a tad better in the unobstructed refractor and the images were marginally more stable as judged by their reduced tendency to morph out of perfect focus as they moved across the field. That said, I was very pleased at how well the reflector held its own; the more prominent diffraction rings having no discernible effects on the resolution of these point sources. And while contrast was a shade better in the refractor, I did not judge it superior enough to warrant a discontinuation of my double star adventures with the 130mm Newtonian. Its wonderful comfort is a huge virtue in this regard.
Comments: The CA described in the daylight tests had no effect on the resolution of these test doubles (an observation well borne out by an enormous body of historical literature), although their colours were slightly distorted (yellowed) compared with the Newtonian(which by nature always delivers true colour images). Indeed, the secondary spectrum was only slightly apparent on Delta Cygni A, being quite a bright star. What is more, I felt it added slightly to the aesthetic appeal of the refractor image over the reflector, but this is a completely subjective judgement.
Test 3: Deep Sky Capability: September 6 2018.
Although the last three nights have been excellent for deep sky observing, I decided to leave this test until the evening of September 6 2018, to make sure no moonlight interfered with the observations. Still, the effort was very rewarding and insightful. As you can imagine, these instruments are very different beasts in regard to their demands on eyepieces. At f/12 even cheap wide angle oculars behave like champs from the centre to the edge of the field and this means that one does not need to splash out relatively large sums of money for well corrected deep sky views using heavy 2-inch oculars. The maximum true field that can be achieved with this refractor from my eyepiece arsenal is 1.79 angular degrees, power 38x. In contrast, the much faster f/5 optical system in the Newtonian requires better eyepieces that can correct for the significant off axis aberrations including coma, astigmatism and field curvature etc. But it is able to deliver a considerably larger true field than the refractor (2.3 degrees with a Celestron X-Cel LX 25mm and 2.5 degrees with a standard 32mm Plossl, though with inferior correction towards the edge of the field).
The closest match I could make to the 38x of the refractor was to couple a 1.6x Barlow to the Celestron X-Cel LX 25mm yielding a 1.44 degree true field and a power of 42x.
For higher power, deep sky comparisons, I employed a 11mm ES 82 ocular in the f/12 refractor and a 4.8mm T1 Nagler (also 82 degree AFOV) in the 130mm reflector, delivering very comparable powers of 139x and 135x, respectively.
Results: Just two targets were examined: M13 in Hercules and The Double Cluster in Perseus. In the low power setting, the refractor offered a slightly punchier image of M13, with slightly greater contrast (darker sky background) than the reflector. The faintest stars in the field were just a tad easier to discern in the big glass than in the Newtonian, but otherwise they were very comparable. At high powers, the results were broadly the same; with the nod going to the refractor, but I was very impressed at how well the little reflector did. If I were to quantify the difference I’d estimate that the 5″ f/12 delivered maybe a 5 to 10% improvement over the reflector on this remote target.
Turning next to the Double Cluster, I returned to lower power. Going back and forth between the images, the views were more comparable than they were different. Contrast was a little better in the refractor, with beautiful pinpoint stars strewn all across the field. The reflector gave almost the same results, with slightly less contrast and colour saturation. The refractor did however pull significantly further ahead at the edge of the field with tighter, better corrected stars, quite in keeping with its f/12 native focal ratio.
Conclusions: This series of tests, comparing two very different instruments of broadly similar aperture is almost never done by amateur astronomers. Doubtless, part of the reason for this is that no one wants to be told that a very expensive refractor could be rivalled by a far less expensive reflector on the same targets. And yet, apart from the clear superiority of the reflector during daylight use, this is very much the conclusion I was forced to draw; the views are very comparable. I believe the results are attributed to the superior coatings on the mirrors which collect very similar amounts of light as well as the relatively small central obstruction in the reflector which tends to keep image contrast high. Had the Newtonian possessed standard coatings, I believe I would have reported a larger difference in their performance on deep sky objects. This, together with very close attention to attaining perfect collimation in the Newtonian readily explains why it performed so well in comparison with the refractor on high resolution point sources, such as double and multiple stars. At the very high powers employed in test 2, the coma free field is much reduced in the reflector, allowing good images to be maintained from the centre of the field to its periphery.
But in all such comparisons, it pays to also consider the comfort factor; that is, how easy the instruments are to transport, mount and manoeuvre in field use. This is where the Newtonian rocks in comparison to the refractor. It is quite simply a joy to use; no hunching behind an eyepiece very low to the ground, no need to re-balance the telescope when it’s pointed to targets of greatly different altitude etc. The small advantages the refractor has over the reflector pale into insignificance when these considerations are accommodated.
Newtonians have clearly come a long way; with modern high reflectivity coatings, quality primary and secondary mirrors and careful attention to collimation and cooling, they compete very favourably with refractors, at a fraction of the cost. I hope you can appreciate why I almost always reach for the little 130mm reflector in comparsion to the refractor. Granted, the latter may look more majestic in the cold light of day, but all this is quickly forgotten under a clear, dark country sky.
Neil English explores four centuries of telescopic astronomy in his ambitious new work (772 pages), Chronicling the Golden Age of Astronomy, due out in October 2018.