Further Adventures with a 3″ Achromatic..

An amazing performer; the Orion SpaceProbe 3 reflector.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Dedicated to John Wall (1932–2018).

a chromatic: literally, without colour.

There has never been a better time to begin the hobby of telescopic stargazing. In past generations, owning a good telescope often proved to be an expensive venture, typically involving many months or even years of saving up. Thankfully, such days are well and truly behind us. Today, you can purchase a decent quality telescope for a very light financial outlay. Indeed, I always advise novices not to spend a great deal on their first telescopes, especially if they are unsure whether or not they intend to pursue the hobby in the longterm. In addition, many people will end up being ‘casual’ or ‘occasional’ observers and so splashing out lavish sums of money on an instrument that sees little net use doesn’t make a whole lot of sense.

In this capacity, one of the best novice ‘scopes I have personally come across is the Orion SpaceProbe 3 reflecting telescope (pictured above, fully assembled), which set me back about £70. That money bought me a very good 3 inch (76mm) telescope, together with a decent mount and two good quality eyepieces delivering magnifications of 28x (using the 25mm ocular) and 70x (when the 10mm eyepiece is employed) and an excellent instruction manual written by an experienced astronomer to show you how to set up the telescope properly, as well as guidance on how to keep the optics in tiptop condition.

All good starter ‘scopes need a good instruction manual.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The Orion SpaceProbe 3 is the latest incarnation in a long line of Newtonian reflecting telescopes, so called because its ingeniously simple design was invented by Sir Isaac Newton around 1668. Over the years, the Newtonian telescope has been steadily improved and refined so much so that today it is arguably one of the most popular kinds of astronomical telescope on the market. Generations of skygazers have enjoyed the crisp, bright images served up by these telescopes, allowing them to conduct detailed observations of a wide range of celestial real estate, from the Moon and the the bright planets, to pretty star clusters, nebulae and distant galaxies in the depths of space.

The optical tube displays the basic optical information of the telescope, including its aperture (76mm) and focal length (700mm).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The Space Probe 3 telescope has a focal length of 700mm and we need to know this number in order to calculate the magnification being used with any given eyepiece. Fortunately, it’s a simple calculation; just divide the focal length of the telescope by the focal length of the eyepiece. So the 25mm ocular produces an enlargement of 700/ 25 = 28x and the 10mm eyepiece provides a power of 700/10 = 70x. Although these will give very pleasing views at ‘low’ and ‘medium’ power, one will eventually need to stretch the magnification some more to get the best views of high resolution targets like the Moon and bright planets. Furthermore, by dividing the focal length by the aperture, i.e. 700/76, we obtain a quantity called the focal ratio of  9.2 or f/9.2. The significance of this number will become important as I elaborate on the optical quality of the telescope in due course.

My field testing over the last two months has clearly shown the potential of this little telescope. A good instrument ought to garner sharp images at powers of 50x per inch of aperture. So according to this reasoning, a 3 inch reflector ought to handle 150x. But I can assure the reader that this telescope can handle considerably higher powers and these high powers can prove very useful for certain kinds of astronomical observations. I have used the instrument profitably at powers of 210x or more but one must also bear in mind that as one pushes the magnification to these high values, the images become rather dim owing to the small 3 inch mirror gathering the light.

By far the most economical way to achieve a greater range of magnifications is to invest in one or two Barlow lenses. Typically they will boost the power of any eyepiece by a factor of anywhere from 1.5 to 3 times. You can get a decent Barlow for just a few tens of pounds (it’s always worth watching out for one on the secondhand market too) and when skillfully chosen, can turn two eyepieces into four or even six. For example, a 2x Barlow will enable the two eyepieces supplied to give additional powers of 56x and 140x. For this particular study, I employed 2.25x and 3x Barlows, providing high powers of 158x and 210x, respectively, when coupled to the 10mm eyepiece supplied with the telescope.

The eyepieces and Barlows used with the telescope. From left to right: the 25mm ocular, the 10mm ocular, the 2.25x and 3x Barlow lenses.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

One of the most attractive features of the telescope and its mount is its overall weight; just 8.4 pounds (3.8 kilos)! That means that most anyone can move the fully assembled about. The lightweight but strong aluminium tripod can be collapsed or extended for seated for viewing or by standing. I decided to use the instrument without its accessory tray so as to maximise the stablity of the tripod. In addition, I elected not to attach the slow motion control bar. This is a strategy I have adopted for many years now, as I like to keep the up−down (altitude) and sideways (azimuth) motions to be as free as possible. With many hours of practice, I have learned to nudge the telescope along smoothly and with minimal vibrations, even at high power. I accept that this is essentially a learned skill  and that others may not be happy with it. Only time spent at the telescope can ultimately sway you in one direction or another, and I would encourage as much experimentation as possible in this regard.

To get the very best images out of this telescope, the user must ensure that the optics are accurately aligned. The user manual and the supplied collimation cap and Philips screwdriver will enable you to accurately execute such a task. Experience shows that once this is done, the telescope retains very accurate optical alignment, even after being moved from indoors to the outside many dozens of times. This fine tuning of the optical train will make a noticeable difference to the high power views especially.

By and large, telescopes are not status symbols. How they look counts for practically nothing in the scheme of things. That said, this telescope is well made and is handsomely finished. It ‘looks’ like a ‘proper’ telescope and performs like a ‘proper’ telescope. The rolled aluminium tube is finished in an attractive British ‘racing green’. Some readers concerned more with appearances than anything else (an ugly reality for some, unfortunately) will no doubt fuss over whether or not it ‘looks the part’ or not and may falsely ascribe importance to what ‘others’ might think. This rather sad state of mind can be entirely dispensed with when one realises that amateur astronomy is very much a small ‘goldfish bowl’. The vast majority of folk I have shared my telescopic experiences with know nothing about telescopes and can’t discern anything from its appearance. Indeed, you’re as likely to find a telescope like this in a New York penthouse balcony than in a tenement of a working class community. Telescopes are just not like cars! So, if you’re concerned about something as trivial as ‘looks,’ you’re probably in the wrong hobby!

To get an idea of how good the optics are in these telescopes, it pays to take the instrument out during daylight hours. I like to observe nature with as many of my telescopes as possible and usually select a good spot in my garden, out of direct sunlight, and give the instrument a few minutes to settle down in its new environment. To work at its best, any telescope must be allowed to equilibrate with its ambient environment. Failure to do so will provide less than optimal (read disappointing) results, especially when the telescope is ‘pushed’ to high magnifications. I recommend starting with the lowest power eyepiece; this will be the 25mm Explorer II ocular supplied with the telescope delivering 28x. I usually select a distant tree top a few hundred yards distant or some such which I can zoom in on. Care must be taken to avoid observing targets over possible heat sources, such as rooftops and the like.

Once a suitable target is chosen, crank up the magnification gradually, carefully touching up the position of best focus by moving the drawtube housing the eyepiece slowly back and forth until the sharpest possible images are produced.

Good focusing is an essentail skill especially when attempting to ‘push’ the magnification of the telescope.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

By engaging in such an activity, I have discovered that the telesope can take high powers in its stride. The images remain crisp and sharp right up to 210x and beyond, especially on bright sunny days. This comes at the expense of image brightness though; higher powers yield progressively dimmer images. This image quality is no doubt facilitated by the high focal ratio of the telescope (f/9.2 in this case). When the focal length is long in comparison with the aperture of the ‘scope, geometrical aberrations are minimised; less field curvature, coma, distortion, spherical aberration, astigmatism etc. This alows for the use of simpler and less expensive eyepieces so that using the telescope will not create a ‘black hole’ with your resources.

Oh deary me!

 

 

 

 

 

 

 

 

 

 

 

In this way, you will discover that this telescope is a very sharp shooter that will embarrass owners of much more expensive telescopes of comparable aperture. The images you will enjoy are true and honest; a simple consequence of the laws of optics and good execution. Here’s an image taken my the US−based amateur, Joe Roberts, who took the time to image the first quarter Moon at prime focus (be sure to click on the image for a good close up) with the same telescope albeit on a sturdy motorised equatorial mount. I hope you will agree that this little telescope is no toy!

More a hindrance than a help: the EZ finder that comes with the telescope.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

One of the Achilles’ heels of this telescope package might not be uncovered until one spends a good few hours in the field. Specifically, many decent−sized telescopes come with the equivalent of a ‘rifle sight’ or ‘finder’ telescope, which usually attaches to a bracket found on the top of the main telescope, adjacent to the focuser draw tube. Once aligned with the main telescope, it serves as a very useful tool to find and centre objects quickly. But the ‘finder’ supplied with the Orion SpaceProbe 3 is not a  telescopic ‘finder’ as such, but a non−magnifying device (the EZ finder) that projects a small red dot onto a plastic screen which the user is required to co−align with whatever object is to be observed in the telescope. However, a few sessions of active use with the EZ finder will convince most of its inadequacy. For one thing, the EZ finder can only be used with the brightest stars and for those who live in towns and cities, where light pollution may be a concern, using it will prove more an exercise in frustration than anything else.

For this reason, I would strongly recommend the user swap this device out for a regular finder telescope; a small traditional finder ‘scope magnifying perhaps five or six times and having an objective (front lens) of about 30mm. These can be purchased on the used market for very little money. Indeed, if you play your cards right, you may find a sympathetic amateur who will provide you with one for free! Mounting such a finder ‘scope will greatly enhance the enjoyment one can have with the telescope. You’ll be able to focus in on much fainter targets, and learn how to ‘star hop’ from one object to another.

Close up of the finder I mated to the scope; note the matching colour and texture of the finder bracket with the focuser and rim of the optical tube assembly. Schmokin’

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Before you can use the finder, it must be aligned with the main telescope. This is easy to do in daylight. Just select a distant target (as far away as posible and at least a few hundred yards in the distance) and centre it the main telescope. Now look through the finder ‘scope and  move the cross hairs of the finder so as  they coincide as precisely as possible with the image in the main telescope. This is usually done by tigtening or loosening a set of screws in the bracket mounting the finder. Once that’s done, move the telescope to a different target and check to see that the subject you have centred in the main instrument is also centred in the cross hairs of the finder ‘scope. If so, you’re ready to rock ‘n’ roll!

The position in which the observer looks into the telescope has a direct bearing on viewing comfort. And the more comfortable the telescope is to use, the more you will use it. In this capacity, the convenient location of the focuser drawtube makes it easy to observe objects situated at low altitudes but it is while viewing targets high in the sky that the great utility of the Newtonian design shines through. As a former refractor enthusiast, I certainly do not miss the extraordinary degree to which one has to crouch down into very uncomfortable positions near the ground in order to view a high altitude target for any length of time. The simple truth is that Newtonians dispense of much of this hardship. Because I value my back and my posture, observing with the Orion Spaceprobe 3 provides a good way forward.

Every budding telescopist needs a guide book of sorts. It can be hard to know what’s what, observing from a bright, suburban sky, and from a dark site, where the full glory of the heaven is manifested, it’s very easy to get confused. That’s where a simple guide to the night sky is so useful. It will be prove indispensable as your knowledge and observing skills develop. There are many good literary guides available to the modern amateur. I especially like Ian Ridpath and Wil Tirion’s Stars & Planets (Collins 2017). It’s strength lies with its simplicity. You can use the seasonal and monthly maps to find the outline of a constellation you wish to explore and then home in on your selected target(s) for the evening. The lunar maps are very good too. Overall, I have found it an invaluable aid to small telescope forays in the northern hemisphere, but is equally at home under an antipodean sky.

The new edition ( October 2017) of a favourite observing guide.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Finally, though it may seem a bit old fashioned nowadays, I recommend that all observers adopt a culture of regularly recording the sights and sensations one experiences while at the telescope. Notes are an important thread to the past.  It’s amazing how much one forgets as the years go by, and it is so reassuring to have the means of consulting earlier work in matters that may prove important at some later time.

 

 

 

 

 

 

OK. With all that said, we’re now ready to begin an adventure together under the stars, exploring something of the extraordinary riches of the heavenly creation. It is fitting to begin this journey with the brightest and most accessible object in the night sky; our glorious Moon.

Oona: a perfect ‘scope for moongazing.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Date: January 31 2018

Time: 22:00 UT

Conditions: Clear, bright sky, very little cloud, bright full Moon.

Temperature: 0C

Tonight is a Super Blue Moon. This means that the Moon is bigger and brighter than average (that’s the ‘super’ bit). It is also the second full Moon in the month (making it’ blue’), the last one occurring on January 2nd last. Inserting the 25mm Explorer II eyepiece and focusing the telescope shows a big bright orb. Indeed it’s almost dazzlingly bright, prompting some observers to reach for a neutral density filter to cut away some of the glare and reduce eye strain. Notice also that the reflected light from the full Moon makes the background sky very bright, drowning out the light of many of its fainter stars.

Did you notice that the image of Moon is both upside down (meaning north is at the bottom and south is at the top) and back to front (meaning east and west are the wrong way round)?

All of this is completely normal with a Newtonian telescope. Indeed, spatial orientation is of little importance in the pursuit of astronomical bodies. You’ll soon get used to it!

Now, looking at the Moon itself with the 25mm eyepiece delivering 28x. Notice how big the entire field is. Indeed, you can easily see that it will fit about three full Moons from one side to the other. Since the full Moon subtends an angular size of about half a degree on the sky, this gives you an idea of how large the field is in the 25mm Explorer eyepiece; about 1.75 degrees. That’s plenty big enough to see the vast majority of deep sky objects, as we shall see on other evenings.

Chances are you’ll have also witnessed two ray craters on the lunar surface. Down near the bottom of the Moon (as you observe it) is Copernicus and the one near the top is called Tycho. Can you see how rays of bright matter seem to stream from these craters? The rays are caused by ejected material gouged out when a large, rocky body collided with the lunar surface in the distant past, ejecting huge quantities of material away from the crater and in all directions (that is, radially). Such ray craters are very old: Tycho is believed to have formed some 100 million years ago, while Copernicus is thought to be 10 times older still (so a billion years or so).

The two prominent ray craters visible in the telescope; seen here in the correctly orientated view.

 

 

 

 

 

 

 

 

 

 

 

Because your telescope is a reflector, it shows the true colour of the lunar regolith. Looking closely at its surface will convince you that it has many shades of white and grey, revealing something of its mineral content and age.

Next, remove the 25mm eyepiece and replace it with the 10mm. After centering the Moon and refocusing; you will note that the field of view is considerably smaller and yet it’s still larger than the size of the full Moon. Indeed, this 70x eyepiece serves up a fairly generous field of view of about 0.7 degrees.

It follows that as the magnification increases for a given eyepiece design, the field of view shrinks.

This observing session will have familiarised you with the magnifications and field sizes for your two eyepieces. These will be useful data as we plan our observations of other celestial bodies.

Alas, observing the Moon while it is full is the absolute worst time to see many of its most inspiring features. To see the great mountains, valleys, craters and rilles; we’ll have to wait until the Moon proceeds through its last quarter and crescent phases. We shall return in a few days when it begins to wane.

Be sure to tune in again soon; you won’t be disappointed!

Date: February 5 2018

Time: 00:35UT

Conditions: good, steady conditions, almost totally clear, cold.

Temperature: −1C

I’ve been watching the Super Ball!

No, that’s not a typo!

It’s a lovely winter night here in the glen. The Moon began to rise about 10:30pm local time, but I waited a couple of hours before beginning observations of the waning gibbous Moon. Charging the telescope with the 25mm Explorer eyepiece, I watched in sheer amazement as our wonderful natural satellite rose above the tree line in the east. Even with the 28x eyepiece, there was a wealth of fine detail to be seen. At low altitudes the air roils quite a bit. That’s totally normal. At low altitudes, you are looking through a dense swathe of air, which generates a bit of turbulence. At these low altitudes, you can even make out subtle colour differences in the lunar regolith. Specifically, the Moon takes on a very light, rose tint. This is also to be expected, as at lower altitudes there is more dust which scatters blue light more than red (a phenomenon called Rayleigh scattering). I find it very beautiful! Compare its colour again when it rises a lot higher in the sky. That comely rose tint all but disappears. Only its silvery face presents itself when it rises above the dust line.

Below is an image of how you should see this waning gibbous in the low power field of your 3″ reflector. I simply rotated and inverted a Wiki Commons image of the Moon at this stage in its phase. That said, I perceive the contrast in the telescopic image to be noticeably better than this image.

The waning Gibbous Moon as seen in the low power eyepiece of the telescope.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

As the minutes pass, the Moon rises higher and the image becomes steadier. When it reaches a decent height, say 15 degrees or so, remove the low power eyepiece and insert the 10mm ocular, delivering 70x. The image should remain nice and crisp and even more detail should be discernible. Use a Moon map to try to identify some of the sights your eye meets with. As the Moon rises above 30 degrees altitude (so about one third of the way from the horizon to the zenith), use a Barlow lens to boost the power still more. If the optics are working half decently and are properly aligned, you ought to get good sharp images at 150x or higher, if the air remains steady. That the images are crisp and clean even at these high powers testifies to the extraordinary value of this economical little telescope.

Intriguingly, February 2018 will not have a full Moon (it will be almost full though lol); something that hasn’t happened since 1999. As if in recompense, March 2018 will have two full Moons though; one on the 1st and the other on the 31st. So March 2018 will present another Blue Moon if you’ve missed the apparition in January.

I like to name all my telescopes. This little one is called Oona.

Wee Oona; ready for action.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Date: February 6 2018

If you follow the phases of the Moon faithfully with the little Space Probe 3 telescope, you’re sure to have an absolute ball. It will serve up beautiful images time and time again. Arguably the best times to observe our natural satellite is between the half−illuminated and crescent phases. You will be astonished at just how much this instrument can reveal!

When taking the telescope and your eyepieces from the cold night air back inside to a warm indoor space, chances are you’ll notice that some condensation may form on the optical surfaces, in much the same way as steam from a kettle fogs up a cold window. This effect of fogging up is more inconvenient than anything else, but you can largely avoid it by capping your eyepieces and the telescope before you bring them back indoors. Under no circumstances are you to rub the lenses or the mirrors while they have dew on them. If you see signs of condensation, just let it evaporate away before capping up the optics. These simple measures will ensure that your equipment will remain in top condition for many years to come.

Observing the Moon is only the first step in enjoying the Orion SpaceProbe 3. As we shall discover, a rich variety of celestial objects are within easy reach of this little telescope. All we need is another clear sky to explore them.

The Ever Changing Sky

The Northern sky on February evenings.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The night sky is constantly changing; minute by minute and hour by hour, as the world turns on its axis and races around the Sun. Consulting the all−sky maps presented on pages 30 and 31 of Ridpath and Tirion’s book, you can see how the February sky appears in the northern hemisphere. Looking south, we see Virgo, Leo, Cancer, Gemini and Taurus, as if in some grand procession, moving from east to west. Concentrating on the constellation of Cancer, the celestial Crab, featured on page 97, I have selected a single object worth investigating with the telescope; The Beehive Cluster (M 44).

The constellation of Gemini in our guide book. M 44 is seen circled near the centre of the consellation.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The accompanying notes featured on page 96 give us enough background information in order to make sense of what the telescope will reveal. M 44 is an open cluster, also known as Praesepe (the Manger), the authors inform us. It is large, covering about 1.5 degrees, and consists of some 50 stars ranging in glory from magnitude 6  and fainter. It even tells us how far away the cluster is; a mind−boggling 592 light years according to measurements made by the Hipparcos satellite. It ought to be visible to the naked eye as “misty patch” from a dark country sky, making it easy to track down.

Time: 23:00−23:30 UT

Seeing: Good, clear, cold.

Temperature: −3C

I took the telescope out for a short spell tonight after work. It remained very clear all day, and on into the evening. It was another lovely vigil with a light dusting of fresh snow to brighten up the landscape. So before the Moon came up, I ventured out when I knew the cluster would be highest in the sky, that is, when it’s due south. Where I live, M44 is a very easy naked eye object. Just like the authors described, it’s a fairly conspicuous “misty patch” that is easily framed in the finder ‘scope and the main telescope proper. Only one eyepiece was used tonight; the 25mm Explorer II, delivering 28x. It framed the cluster perfectly, where dozens of stars of various degrees of glory pepper the field of view. And it’s not at all hard to see why its more popular name, the Beehive Cluster, is alive and well.  With a little concentration, you can make out a soft, yellow colour in the brighter members; a good sign that this cluster is fairly mature in the scheme of things. I made a simple sketch of what it looked like (see below). If you are warm and comfortable, sketching can be a whole lot of fun, even in the cold of winter. I simply try to memorise what the field is like for 10 or 15 minutes, nudging the telescope along with one finger as the Earth rotates beneath my feet. Once I’m indoors I make the sketch. Little Oona frames lots of things in the sky very well.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

There are, of course, other ways to make a sketch. Many sketch while at the telescope. In order to do that, it’s advisable to protect your night vision as much as possible. You see, in the dark, your pupils dilate to take in as much light as possible. This is a natural biological response to low light conditions. Fortunately, red light does not appreciably interfere with this dark adaptation and so many amateurs choose to make their telescopic sketches of deep sky objects under the illumination of a low intensity red light source. Whatever way you choose to carry out your sketches, I hope you will find the activity both relaxing and rewarding.

Date: February 8 2018

Some Musings on Optics

Anyone who has spent a decent amount of time with this telescope and knows how to keep the optics well aligned will surely tell you that the images are exceptional for its meagre monetary value. The reason for the low cost is the simplicity of the optics. The prmary mirror is spherical rather than a true parabola. Spherical surfaces are much easier to execute well in comparison to their parabolic counterparts, which need further figuring to ‘deepen’ the centre of the mirror. But if its aperture is kept small and the focal length is large in comparison, there is absolutely no need to modify the sphere into a parabolic shape. To get an idea of just how good a 76mm (3″) mirror with a focal length of 700mm can be, take a look at a computation made by OSLO (an optics package);

An OSLO analysis of a perfect 76mm f/9.2 spherical mirror. The reader should concentrate on the red underlined data in the lower box.

 

 

 

 

 

 

 

 

 

 

 

 

If your mirror is a perfect sphere then you have a wavefront rating of 1/12.5 PV. Put another way, a completely error free mirror with these specifications would have a Strehl ratio (seen on the right above) of 1.0. The analysis shows that the actual value is shockingly close to absolute perfection: 0.97!

The conclusion is very simple to interpret: small aperture and long focal length spheres are so close to a parabola it makes little difference.

Of course, we also need to consider the aberrations introduced by the secondary mirror, but suffice it to say that unless the secondary is a complete lemon, it’s very likely that the overall quality of the optics will be very high indeed, good enough to impress anyone who takes the time to spend a few hours with it.

Star testing provides a good way to test how well the optics behave in the field. To do this, make sure the telescope has accurately aligned optics and has had time to cool down outside. Next, select a bright, first magnitude star, situated high up in the sky. For example, Capella is just perfect from my far northerly location. Select a high power; anything between 100x and 150x and carefully focus it. You ought to see a tiny sphere (the so called Airy disk).

The Orion Spaceprobe telescope supports the secondary mirror using a 3 vane spider (b above) and yields six diffraction spikes that are very hard to see except round the brightest stars.

 

Now, if you slowly rack the focuser inward, you will begin to see a set of concentric, Fraunhofer diffraction rings around a dark central spot.The shadow of the three spider vanes will also be seen.

And when you then rack the focuser outward, past the position of precise focus, the diffraction pattern should look identical (or almost so). This is what you want to see in a telescope offering very good to excellent optics. Star testing can provide much information about your telescope, but it’s always best to conduct such tests under the best conditions your local environment will provide, and (preferably) over a few nights. If you don’t get such textbook perfect results, don’t fret. I mean, if you’re already happy with the high power images your telescope is serving up during the day, and again by night, you have a winner and you needn’t worry any more.

Oona star tests very well, showing that her optics are of very high quality. Mass production has clearly come a long way with these little telescopes!

Date: February 9 2018

Time: 19:15 UT

Temperature: 0C

Conditions: good transparency, mostly clear, breezy

Orion is a majestic constellation to explore with a small telescope.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

It was a bright and clear day today and the the sky has remained largely cloudless after dark. The mighty constellation of Orion the Hunter is now approaching its highest point in the sky so is nearly due south. It will present a good opportunity to examine an entirely different kind of deep sky object. Tonight, we will pay a visit to the Great Nebula in Orion. Our guide book on page 197 shows me exactly where to look: immediately beneath the middle star in the Hunter’s belt. The notes of page 198 inform me of some sensational facts about this target; the object, known also as M 42, is a gigantic ball of gas lit up by young stars that are forming inside it. The authors say M 42 lies about 1500 light years away and that it is almost 20 light years across, and much more. Time to set up the telescope once again for another adventure under the stars.

Time: 20:30UT

The Great Nebula in Orion is also easy to spot with the naked eye. A couple of seconds of scrutiny will convince you that it is quite unstarlike; more like another ‘misty patch’ than anything else. Starting with the 25mm Explorer II eyepiece, the telescope clearly reveals its nebular nature surrounded by quite an assortment of bright stars. If you carefully focus on the nebula, the same eyepiece should allow you to just make out four distinct stars at the centre of the nebula; this is the famous Trapezium; very young and hots stars that are estimated to be only a few million years old. They formed out of the cool gas that surrounds them. Ordinarily, a gas cloud is not luminous in and of itself. It is only by virtue of the radiation from the stars that form inside it that renders it visible, just like a neon light bulb.

Now switch to the 10mm Explorer II ocular for a better view of this magnificent structure. At 70x, it is much easier to see the four stars making up the Trapezium, as well as much greater detail in the nebula itself. My eyes can clearly discern colour within the nebula; a very pale green. The colour becomes easier to discern as one’s eyes adapt to the darkness. The visual colour of M 42 is quite unlike that produced by a CCD camera, which picks up vivid blues, pink and red, owing to its greater sensitivity to light. Still, just detecting some colour provides a real visual thrill.

Just to the north of M42, my eye meets with a ‘fuzzy’ star. This is in fact another nebula; M 43.  After several minutes of study, slowly nudging the telescope along as the object moves westwards through the field, I made a quick sketch of my impression of the view as seen through the little 3″ reflector.

M 42 as observed on the evening of February 9 2018 using the 76mm f/9.2 reflector. South is at the top and west is to the left.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Larger telescopes will give even more compelling views. That’s because larger telescopes collect more light and deliver that light to your eyes. A fully dark adapted human eye allows your pupil to dilate to about six or seven millimetres. That is the maximum ‘aperture’ of the human eye. But when you look through the telescope, that 7mm is replaced by a mirror fully 76 mm in diameter! As you can imagine, it collects many times more light than you can with your naked eye because its light collecting area is so much greater; and that allows you to see much fainter objects.

The orion SpaceProbe 3; a wonderful little light cup.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Date: February 11 2018

Time: 21:10−21:20 UT

Conditions: turbulent, frequent sleet & snow showers, very cold in the wind.

Temperature: −1C

Oona(right, background), accompanied by Octavius, my newly flocked and insulated 8−inch f/6 Newtonian reflector.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

I spent Saturday afternoon lining the inside of my 8 inch f/6 Newtonian reflector with cork and then covered it over with flocking paper. This evening, I decided to test drive the 8 inch, which I had planned to use along side the 3 inch reflector, but the frequent interruptions from snow showers forced me to retire the larger instrument after about 15 minutes; I did however gather some useful data on a few tricky double stars.

Because the 3 inch telescope is so lightweight and ultraportable, it was the ideal instrument to use in these very mercurial conditions. And it allowed me to greatly extend my gaze. Everything we have visited thus far with the 3 inch reflector lies entirely within our own galaxy, the Milky Way. Tonight though, I spied the Plough asterism looming large in the northeastern sky and decided to try my hand at tracking down the famous Messier duo, M 81 & M 82; a wonderful pair of galaxies located at a distance nearly four orders of magnitude further away than even the Great Nebula in Orion!

Charting a course.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The pair is easy to track down in a dark, moonless sky. Consulting my guide book on page 251, I was able to chart a course for these fairly easily, by drawing an imaginary line from Phecda through Dubhe, and extending that line about twice as far again until I arrived at my destination. Tucked away in an otherwise fairly barren sector of the firmament, my finder could easily make out 7th magnitude M 81, and, with a wee bit more concentration, M 82 also. Once again, only one eyepiece was used this evening; the trusty 25mm Explorer II eyepiece, which easily framed the duo, separated as they are by about 0.6 angular degrees of sky. M 81 looks fuzzy and elliptical in shape, brightest near its centre and gradually fading towards its edges. M 82 to its north presents as completely different however; more cigar shaped than elliptical. After a while studying the pair, you may come away thinking that M 82 is easier to study, even though it is about four times fainter than M 81. Both galaxies lie at a distance of 12 million light years; an utterly unfathomable scale.

I made a quick sketch, shown below, of M81 and M 82, and its hinterland through the SpaceProbe.

Messier 81 & 82, as seen through the 3″ f/9.2 reflector on the evening of February 11 2018.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

There are many more galaxes within reach of the little achromatic, and which will take us even further afield. Best to wait ’til better weather sets in though.

Date: February 14 2018

Time: 20:40UT

Temperature: 4C

Conditions: Mostly clear, some cloud interfering with observations, milder than of late, windy.

After enjoying a romantic Valentine’s supper together with my wife, I ventured outside to see how the sky was shaping up, and as luck would have it, it seemed very inviting to continue our adventures under the stars with the Orion SpaceProbe. As promised, we’re going to try our hand at objects significantly farther away than our former targets; specifically,  a trio of galaxies in the constellation of Leo the Celestial Lion, which will be very well placed later this evening. These galaxies are located about three times farther away than either M 81or M 82, so about 35 million light years distant from our galaxy, the Milky Way.

Our targets tonight are located in southern Leo, shown just above the tip of the pencil in this photo.

Consulting my guide book on page 169, I can clearly see the location of these galaxies; M 95, M 96 and M 105; which should be captured in the low power (28x) field of the 3 inch telescope. That said, these island universes are considerably fainter than M 81 & M 82 and so will be a bit more challenging to see (my guide book quotes both M 96 and M 105 as having a magnitude +9, whereas M 95 is fainter still at + 10).

I shall report back later to tell you how I got on. Fingers crossed!

Time: 23:45UT

Alas, it has totally clouded over, so I will need to abort this activity tonight and try again another night.

Date: February 15 2018

Time: 14:00 UT

The weather is not always in harmony with human ambition. Meteorology may be a mature science, but it can’t yet be relied on with 100 per cent accuracy. There will always be discrepancies between what the forecast predicts and what you actually experience. It just comes with the territory of any amateur astronomer. That said, such episodes cultivate patience and preparedness; virtues in their own right.

It is a New Moon today, so a thin crescent should appear in the sky over the coming evenings. But once that Moon sets, it will be good and dark enough to ferret out those galaxies in Leo. I will report back again as soon as an opportunity presents itself.

Date: February 16 2018

Time: 00:30UT

Conditions: quite windy, some clear spells, remaining more mild than of late.

Temperature: +4C

I managed a short spell with the SpaceProbe just after midnight. By then, Leo had moved into a favourable position in the south southeast. I centered the finder ‘scope on the star 53 Leonis, which lies just south of the targets in an otherwise rather empty region of sky. Then, charging the 3 inch with the 25mm Explorer II eyepiece, I nudged the telescope about one angular degree to the north norhwest and scrutinised the field for signs of faint fuzzies. Sure enough, both M 95 and M 96 show up well in the little SpaceProbe at 28x. The more easterly M 96 is slightly brighter than M 95. The latter appears rather circular with a noticeable central condensation. To my eye, the fainter M 96 looks a wee bit more elongated along its north−south axis. Both of these objects are classed as barred spirals. Moving these galaxies to the southern edge of the field, your eye will pick up the the giant elliptical galaxy M 105, appearing as a faint glow.

Although the strong gusts of wind and the constant interruption from clouds prevented me staying out for very long, you can visit another delightful trio of galaxies directly east of these objects; specifically M65, M66 and NGC 3628, also featured on the map above. All shining with magnitudes of about 9, they present as an equally challenging target for the 3 inch reflector. Do give them a visit if your skies permit.

 

To be continued………………

 

De Fideli.

Changing Culture V: Using Newtonians in a Terrestrial Setting.

See the difference.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

In a previous blog, I described, in considerable detail, my enthusiasm for the lightweight but powerful 130mm f/5 Newtonian reflector. This modest instrument beat the codpiece off a way overpriced 90mm ED apochromat which retailed for about £1,000 (and is now discontinued) on every test object. This little Newtonian has an excellent SkyWatcher parabolic mirror and the secondary was upgraded to an Orion Optics UK sourced unit, with a semimajor diameter of 35mm, thus delivering a moderate 27 per cent linear obstruction (so considerably smaller than a similarsized SCT or Maksutov). Both mirrors were also treated with Orion UK’s proprietary HiLux coatings, providing an overall reflectivity of 94 per cent. Further testing showed that it provided images that were effectively equal in brightness to a fine 127mm f/12 refractor (which has now been retired). The interior of the tube was lined with cork for improved insulation and then covered with standard flocking paper, maximising contrast and reducing stray light to near zero.

Such an instrument has provided excellent views of the heavens, from 20x in a 2.5 degree true field, to over 400x on very tricky double stars down to 1.0″ separation. During last year’s apparition of Jupiter, the 130mm f/5 Newtonian also proved its worth as a very capable planetary telescope. The instrument was also fitted with easytouse Bob’s Knobs on both the primary and secondary for ultraprecise collimation that takes just seconds to execute.

Newtonians need to be very well flocked to serve as effective terrestrial telescopes.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

It may come as a surprise to some readers to learn that this author spends as much time looking through telescopes by day as by night, and over the past few months, he has been using the 130 as a ‘super’ spotting ‘scope, where it has dlivered crisp, colourtrue images of a range of terrestrial targets, including, birds, trees and various manmade landmarks. This has led him to openly question the dominance of more conventional spotting ‘scopes (usually small refractors and catadioptrics). The only reservation I had while using the Newtonian for nature studies was that it delivered an image which was upside down and rightleft reversed. And while this ought not to bother a determined telescopist, some have dismissed the small Newtonian as a daytime spotting ‘scope precisely because of the orientation of its images. Yet, there are ways to produce correct orientation views through Newtonians and it doesn’t require expensive prism diagonals and the like; enter the Newtonian erecting eyepiece.

The SkyWatcher 10mm Newtonian erecting eyepiece.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

I was able to get hold of a 10mm focal length ocular marketed by SkyWatcher for less than £30. It has basic but effective antireflection coatings and appears to consist of a simple Kellner design with an extra lens inserted so as to invert the image at the focal plane and, unlike conventional refractor diagonals, it flips the image so that left and right are correctly presented.

The 10mm SkyWatcher erecting eyepiece has basic anti–reflection coatings.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The eyepiece delivers a power of 65x, with a near 2mm exit pupil, which closely matches the diameter of my pupil during bright daylight. Optically, the unit delivers good, sharp images, with a welldefined field stop, although critical tests did reveal a small amount of lateral colour. Contrast is good but not quite in the same league as a dedicated astronomical eyepiece endowed with fully multicoated optics. Yet, it is more than adequate for casual nature studies.

The instrument can be focused on objects as near as 25 yards without adjusting the position of the ocular, but by moving the eyepiece further up the barrel, or using the supplied extension tube (pictured below),objects even closer to the telescope can be brought to a good focus.

The extender tube supplied with the 10mm SkyWatcher erecting eyepiece.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Doing an internet search, I have also become aware of a 20mm model (supplied by Celestron with some of their smaller Newtonians), which would produce a power of 33x or so with the 130. This would be a useful addition for those wishing to extend the range of magnifications achievable with the telescope during daylight hours, and I will report back on this if I am lucky enough to find one.

So to summarise, there is absolutely no reason why observers possessing small Newtonian reflectors cannot use them in a variety of terrestrial applications. Their increased light grasp and resolution over conventional spotting ‘scopes and small refractors will both surprise and delight their users. The range of terrestrial eyepiece options available are quite limited at the moment (as far as I can tell) though, but I would warmly welcome the introduction of more models offering a greater range of magnifications, as well as improving the optical quality of these designs. But one thing is clear; using erecting eyepieces increases the verstaility of what is, already, a great, allround ‘scope.

 

Neil English is the author of Grab ‘n’ Go Astronomy.

 

 

 

 

De Fideli.

Some Experiments in Thermal Management with a Newtonian Reflector.

The author’s 130mm f/5 Newtonian reflector enjoying a winter wonderland.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Preamble

Introduction

As explained in earlier blogs, I have discovered, through extensive experience in the field, that Newtonian reflectors can render beautiful, colour free images of a wide variety of celestial objects, from the Moon and bright planets, to a wealth of bodies beyond the solar system. In my own niche area of double star observing, I found that a simple 130mm f/5 Newtonian reflector resolved tighter pairs than a 90mm ED refractor and indeed, as deduced from my previous field notes, also exceeded the performance of a very fine 102mm f/15 classical achromat on good nights of seeing.

Refractors have a well earned reputation for garnering very stable images at the eyepiece, a consequence of the decent height of the entrance pupil above the ground, glass properties (crown & flint doublet objectives in particular), less intense tube currents and relatively small apertures which are quite often immune to the vagaries of the atmosphere. In comparison, reflectors can be rather temperamental. With their need for precise collimation and greater tendency to manifest thermal effects coupled to the (often) larger apertures employed in the field, Newtonians typically (but not always) serve up images significantly more unstable from moment to moment.

As I also explained before, this is not really a big issue for a seasoned observer, who has more than enough patience to remain observing long enough to ignore or wait for the disappearance  of these various bugs that attend the use of a good Newtonian telescope. That having been said, I elected to investigate the effects of some simple modifications that could potentially ameliorate the effects of tube currents in the 130mm f/5 Newtonian, so as to stabilise its images as much as possible.

This led me to investigate the effects of insulating the inside of the thin, rolled aluminium tube that houses the optics of this small Newtonian. My researches led me to explore the properties of cork; one of the best, natural and renewable insulators from the Creation.

I heard many a yarn recounted by veteran observers, that lining the inner tube with cork could dramatically dampen the effects of tube currents in Newtonian and compound telescopes. It seems to have originated sometime in the late 19th century or early 20th century, but in more recent years, some amateurs, whose work I trust, have also recommended cork as a suitable insulator for their telescope tubes.

The theory is fairly simple; the thin aluminium tube is an excellent conductor and radiator of heat. Indeed, under a clear sky, the temperature of a metal tube rarely tracks the ambient air temperature perfectly but instead can often fall off to a few degrees lower than the surrounding air during radiative cooling in the field. But by lining the inside of the tube with some kind of insulating material, one can keep this temperature differential between the aluminium tube and ambient air to a minimum.  This should create more stable images, especially at the highest powers, which would in turn make their visual study more profitable, as well as increasing their aesthetic appeal.

Materials & Methods

I checked out what types of cork were available and settled on the purchase of self adhesing cork sheet, which arrived promptly from the seller. Next, both the primary and secondary optics as well as the focuser were completely removed from the aluminium tube, which was then lined with the cork sheet.

Thin sheets of self adhesive cork can be purchased inexpensively from many retailers.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Initially, I had just intended simply to paint the cork a flat black colour but was unconvinced that it was really dark enough to compare with regular flocking material. I therefore elected to cover the cork with the flocking material, which, in effect, would act like a double layer of insulation. After lining the tube with the cork overlaid with the flocking material, I also lined the drawtube of the focuser with more flocking material before putting the telescope back together again.  I was very pleased at the light dampening properties of the instrument  during daylight hours and noted that the images served up by the telescope were a little bit more contrasty than before the flocking material was added. The result is seen below:

The wonderfully dark interior of the telescope tube to improve image contrast.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Finally, I was now ready to study the images of a variety of high resolution targets to see whether or not this tube insulation worked in practice. My tests were carried out over a number of winter evenings, where the ambient temperatures sometimes fell to −10C. Most of my observations were conducted on the evenings of January 18, 19, 20 and 24, but also included some shorter vigils during more unsettled spells. The telescope was given time to cool off to near ambient before commencement of observations.

The targets included some tricky double and multiple stars; theta Aurigae, delta Geminorum, iota Cassiopeiae, as well as  easier subjects like Castor A & B. In each case, I charged the telescope with a power of beween 260x and 406x diameters (so between 52 and 80x per inch of aperture) and the images studied as they moved across the field of view.

Results:

The carefully focused stellar images were very impressively presented in the telescope and appeared significantly calmer (read less susceptible to thermal degradation) as they moved across the field, their forms morphing significantly less than I had previously noted in the uninsulated tube. Indeed, during these vigils I enjoyed some of the finest images  yet garnered from this modest telescope. Specifically, the stellar Airy disks were much more in keeping with those I have enjoyed during the milder months of Spring and Summer. I was able to pick off faint and close companions much more easily and efficiently than I can remember when using the same optics in previous winters. The activity of insulating the inner metal tube most definitely improved the images from moment to moment, allowing me to enjoy their perfect forms for longer.

Further Comments

My correspondence with some highly experienced observers also alerted me to other ways tube currents could be minimised or even completely abated in Newtonians, including housing the optics in an oversized tube, constructing non cylindrical tubes (think hexagonal designs) and using active mirror cooling. A combination of all these strategies have been shown to improve image stability in reflectors and are well worth investigating in their own right. They will surely make an already good telescope into an excellent one.

I intend to insulate my larger Newtonians in the same way, and in due course.

 

The author would like to thank Martin Mobberley and Garyth64 for interesting discussions on cork.

 

De Fideli.

Collins Stars & Planets (5th Edition): Book Review.

The new edition ( October 2017) of a favourite observing guide.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Collins Stars & Planets (5th Edition, October 2017)

Publisher: William Collins

Authors: Ian Ridpath & Wil Tirion

ISBN: 978 000 823927 5

Book size: 400 pages

Retail Price: £19.99 (UK)

The urge to study the sky transcends national boundaries, and so it should. The skies are open to us all.

pp 2

It’s been ten long years since I last purchased my field guide to the stars: Ian Ridpath & Wil Tirion’s 3rd edition of Stars & Planets. Travelling with me the length and breadth of the country and also on a few overseas trips, this pocket sized guide has proven indispensable for my grab and go excursions under the night sky. Alas, the wear and tear over the last decade is now definitely showing. The binding has now come loose and the pages have become heavily soiled from excessive handling. So, I figured it was high time that I got a new copy of this well received volume, and was delighted to see that it was now in its 5th edition (October 2017).

Stars & Planets is the result of a fruitful collaboration between the British amateur astronomer, Ian Ridpath, and an illustrator, Wil Tirion, living in Holland. In keeping with earlier editions, the first two thirds of the work consists of comprehensive maps of the night sky (both northern and southern hemispheres being readily presented) as they appear from month to month. In addition you will find fairly simple maps of all 88 constellations that grace the night sky, together with a list of interesting objects; some brief mythology, as well as notes on their brightest stars and deep sky objects within reach of a small backyard telescope. The full panoply of celestial objects are represented, including  a suite of pretty double stars, open clusters, emission nebulae, globular clusters, the brighter galaxies and planetary nebulae.  What particularly attracted me to the earlier edition was the relative simplicity of the maps; they were clearly designed to be used in the field where they present the basic outline of each constellation, as seen with the naked eye from a reasonably dark country sky. This enables one to easily ‘star hop’ from one object to the next. Striking a balance between adequate content and clear presentation, it is ideally suited to casual observing, adopting a low tech (my particular favourite) approach.

Each constellation shows the main deep sky objects accessible to an observer with a small, backyard telescope or binoculars.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

I was delighted to see that the latest edition retained this same format, only that the maps are now presented with noticeably better contrast against a darker blue sky background. The introduction is filled with basic but very comprehensible facts to help you make sense of how the sky ‘works,’ as well as providing excellent notes on star names (both common and the Greek lettering system), how the planets move in the sky as well as such interesting topics as precession of the equinoxes. The final one third of the book covers information on practical astronomy, including a no frills overview of telescopes and binoculars, observing double and variable stars, comets and meteorites, the Sun, and the planets, including a brief overview of sky transparency and astronomical seeing. Here you will also find a very well laid out section on lunar observing, with plainly presented maps of the particular lunar sections that can observed as it grows from a thin crescent through to full Moon.

Overall, the content is ideally suited to those having small telescopes (60mm to 100mm aperture) and binoculars, with virtually all the objects being well seen with a telescope of just 6 to 8 inches in aperture. The volume is handsomely illustrated throughout, with very high quality images of a wide variety of heavenly bodies; both in the solar system and far beyond. While these are strictly not necessary in a field guide, they certainly improve the overall attractiveness of the book. My only criticism of the work is that the binding is the same as in earlier editions, and so will surely come loose with extensive handling. It would have been better to produce this with a simple ring or sewn binding for greater durability in the field.

For busy grab ‘n’ go observers.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Overall, I highly recommend this book as a conveniently small (for travel) but excellent field guide to the night sky that will be appreciated by either novices or seasoned observers alike. It’s strength lies with its simplicity and will keep a busy amateur happy for many years.

 

 

Neil English’s ambitious new historical work, Chronicling the Golden Age of Astronomy, will be publised later this year.

 

 

De Fideli.

The War on Truth: The Triumph of Newtonianism.

Octavius; the author’s tried and trusted 8″ f/6 Newtonian on its ‘pushto’ mount.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Preamble

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.

Alan French

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 [2]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.

Con Stoitsis
Director
Comet Section
Astronomical Society of Victoria Inc
Melbourne, Australia

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!

Source here.

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.

Barry Fernelius, from this online thread discussing Stargazer Steve’s kit ‘scopes.

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.

Mircea Pteancu from an online thread entitled: Double Stars in the Hind 158mm x 1240mm.

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.

Visual
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.

Photographic
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.

Visual
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.

Photographic
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.

Visual
This object was observed as split using an 8-inch reflector at 340x (3.5XW lens).

Photographic
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

 

Currently, my only objections to the short f/ratios becoming common are that the depth of focus is very short, making focus variability in mediocre seeing a bit more of a problem than in longer f/ratios, and that most eyepieces don’t perform as well at the edges at f/3 as they do at f/5, even when both are Paracorred with the latest Paracorr II at the correct setting. But, that being said, I would still unhesitatingly choose a fast f/ratio at the really large sizes of scope simply because it’s easier and safer to stand on the 3rd step of a step ladder than it is to stand on the tenth (!), and I’ve done that in a 36″ f/5.
Along the way of large scope progress have come better cells, thinner mirrors, better fans, and better collimation tools. Put those all together, and the performance level of the large scopes seems now to be only limited to the mirror qualities, and there are makers of large mirrors now who put the same quality into their mirrors as some of the better makers who stop with much smaller sizes.
I truly wish many of you had seen the poor quality large scopes over the years that I have seen. If you had, you’d realize how we truly live in the Golden Age of Astronomy right now.
Don Pensack, from a thread entitled: Large/Fast Newtonian Mirrors and Quality.
I thought I wanted a 140 class APO. The image and fantasy of it has been kicking around in my mind for most of the year. They’re such nice looking telescopes – what a telescope is supposed to look like. At a major star party a few weeks ago, I found a beautiful 140 – a very well-known top quality model mounted atop a big G11 and I asked the owner if he would please show me M15 in it. He was proud to do so and we looked. He raved and I was silent. I thanked him and walked back to my premium 16″ Dob. Looked at M15 in the 16 and raved to myself saying I’m so glad I have the 16. For the same amount of setup and money, what a difference!
Peter Natscher, Central Coast, California, from an online thread entitled; How much increase in aperture to see a difference?
 Ps. Peter is the proud owner of a couple of large premium Dobs and an Astrophysics 175 EDF apochromatic refractor.

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.

Mr. Hardglass.

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:
TeleVue 140
NP-127
One of only two Christen 6″ f/15 folded Triplets
Takahashi FC-125
Takahashi FCT-150
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), 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.

Quest Do Not Delete, from an online thread entitled.Refractor Equivalent to a 8″ Reflector.

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.

If you are talking about a ~5″ Apo like a 120ED, then yes they do give very nice views, but the 8″ f/6 Dob will still show you more detail and at 1/4 or less the price.

I think the views in the 5″ f/9.4 achro refractor I have are good, and on some nights they really are very good, but I have done quite a few side-by-side comparisons with my 10″ Dob over the past few months and as a result…the frac is back in it’s case in the shed and the Dob is by the back door ready for action whenever there is a break in the clouds.

RikM, (Gloucester, England), from an online thread entitled: 1st Planetary scope: Refractor vs Dobsonian.

Quote: “f-ratio is important. A 6″ f/11 might very well best an 8″ f/5 on most typical nights observing planets,” End quote.

Focal ratio is not relevant it’s the size of the obstruction that matters. So long as the secondary obstruction is under 20% of the primary diameter by area, the scope behaves like an unobstructed instrument. More than 20% and you start to see its effects. The effect you see isn’t due to light loss it’s due to increased diffraction caused by the large circumference of the secondary. This decreases contrast. However, there’s no reason a 25% or even 30% obstructed scope can’t perform very well. Why? If the scope is already a large aperture instrument with good optics then even with a hefty central obstruction it can still show superior contrast and detail. Optical quality and aperture matter more than focal ratio. I see this every time I observe Jupiter at f/4.

Umadog, (Basel, Switzerland), from an online thread entitled, 1st Planetary scope: Refractor vs Dobsonian.

My Skywatcher 8″ F/6 Dob beats my 5″ F/8 Apo [Takahashi FS 128] on the planets ……

post-13701-133877687106_thumb.jpg

Dweller, (Lancashire, UK), from an online thread entitled: 1st Planetary scope: Refractor vs Dobsonian.

 

Indeed, this is the point. The reason that beginners should be steered toward f/6 Newts is because this is a cheap way of getting good images. The mirrors are easier to make well and the eyepieces need not be expensive. Coma correctors aren’t necessary. Large (and fast) can be better, but quality is a lottery if you’re buying Synta or GSO, although those manufactures can produce some nice stuff. If you go home-grown you have a much better chance of a good mirror but you’re paying a lot more for it. In the end a lot of this comes down to economics not optics. Finally, there’s the hassle factor. To get the best out of a refractor you don’t have to do anything very special. To get a good view out of a Newt (particularly a big one) you have to plan ahead with cooling and collimation.

Umadog, (Basel, Switzerland), from an online thread entitled, 1st Planetary scope: Refractor vs Dobsonian.

If you have been dreaming of the day when the Chinese are able to make a portable 8 inch APO for under a thousand quid, keep dreaming! Seriously, this is not going to happen any time soon because APO-quality 8” ED blanks from the major suppliers (Ohara and Schott) don’t exist and if they did would be hideously expensive. Even if the glass was available, big APO lenses will always need a lot of highly skilled hand finishing along with very careful assembly in a sophisticated cell. The only major suppliers of big APOs today – TEC and APM/LZOS – charge the price of a new BMW for an 8” and if that situation changes it will be because they start charging even more! Then there’s always the Takahashi FCT-200 with a list price of $125,000 (but at least it includes the mount).

On the other hand, if you dream of getting similar performance to an 8” APO for under a thousand pounds, then dream no longer. Long focus Newtonians have always been simple to make well and with the advent of interferometer testing they can be made to an exceptional level of optical quality. Add in the possibility of a very small central obstruction, easy collimation and just two light scattering surfaces and a long-focus Newtonian has the potential to perform closer to a big APO than almost any other design.

Roger P. Vine (Welwyn, England), from an online article entitled;Orion Optics 8 inch Planetary Dobsonian Review.

In a Newtonian 8″ to 12″ with small central obstruction under 20%, very thin spider, longish F ratio above F6, excellent tube construction with well ventilated mirror and a decent flotation mirror cell (no mirror glued to plywood). Shorter F ratios require that the object be exactly centered in the field to avoid comatic aberrations. Also, the shorter the mirror, the more you will have to fiddle with the collimation. The mirror should have the best coating you can afford, avoid cheap coatings that lose contrast over time. Get a coating that you can clean without introducing pinholes. Add to that a smooth functioning focuser and you will have a very effective planetary instrument.

Roland Christen (founder of AstroPhysics, IL, USA), from his online article entitled: What is the Best Planetary Telescope?

I’ve compared my ED120 refractor (4.7″) with a number of Newtonians and have concluded that it will match a good 6″ Newtonian in planetary and lunar detail but the additional aperture will show deep sky objects just a little better.

John Huntley, from an online thread entitled: 150mm Refractor versus 200mm Reflector?

I am a confirmed dobaholic so the only choice is an 8″ dob between these two. The issue really is that unless spending 10x your budget or more, a 150mm refractor will provide less impressive views of low power faint objects and more faults with high power bright objects than an 8″ Newtonian. I’d also consider it more unwieldy and heavy/difficult to use than an 8″ dob. The one exception to the above is for wide open clusters where the frac will provide slightly more attractive views I think.

For me at that sort of budget an 8″ newt/dob is about as good as it gets.

Moonshane, from an online thread entitled: 150mm Refractor versus 200mm Reflector?

 

I’m a refractoholic but I have to admit that Shane is perfectly right on all counts.

Olly Penrice, from an online thread entitled: 150mm Refractor versus 200mm Reflector?

My STS and his have been under the dark skies of Landis a few times since. On one particularly memorable occasion, in May of 2015, our Teeters were out there alongside two world-class apochromatic refractors, the FS-128 and the comically coveted AP130. Given all the high-end gear, it felt like some star party of the aristocracy. My friend, who knows next to nothing about telescopes, was on hand. How could he possibly fathom the privilege of looking through such fine gear. Not until several years in the hobby, did I get my first eyepiece time with an Astro-Physics refractor or a Newtonian with Zambuto optics. There was, in fact, a 5th telescope on hand: a 4.5” Tasco — hey, every aristocratic star party needs a peasant scope. The FS-128 owner kept trying to pawn off the Tasco to my friend but he refused. (My friend later regretted not taking it). The modest scope did show Saturn nicely. In fact, on this night the seeing could not have been better. We were all treated to awe-inspiring views of the ringed gas giant, arguably the best I’ve ever had. On this night, Saturn would have looked great in about anything, but the two best views were to be had by the Teeters. My friend, who had no skin in the game (so to speak) or reason to be biased, attested to the “cannon ones” affording the best views of Saturn.

Daniel Quirin, from his online review of the Teeter STS18 (8″ f/6) Newtonian.

Once again, these Newts just floor me! Refractors will always be beautiful, but it’s hard to justify a $250,000 refractor to an $8,000 Newtonian that’s beating it. The fact is, is that if you dial the Newt right, your gonna win. Pons has been observing planets for 50 years. He’s earned the right to decide what he thinks is best and he’s got the best of both worlds to prove it.

When I asked him which scope he liked better on planets, he said the Newt was king, hands down and it’s as simple as that. He has no shame in saying so, d[e]spite the fact that he’s spent a good part of his life and a lot of money building the refractor.

People always try to challenge me in a debate. Then they look through one of these Newts and they’re quickly silenced. Pons always told me that they’ll always try to argue, but they’ll quietly go back to their garage and start trying to build a perfect Newtonian on their own.

Daniel Mounsey from an online thread entitled: Refractor vs. Reflector?

 

Yes, a 4-5″ APO will be very good, but the smallest detail it will resolve on a planet is around the 1 arc-second diameter mark. Resolution is tied intrinsically to aperture. It doesn’t matter how good the optics are or whether you’ve got 99.8% Strehl ratio optics etc, it won’t (indeed can’t) do better than this.

A clean, well-cooled and collimated, say 10″ f/6 or f/7 Newtonian with quality optics around 1/25th wave RMS mark and a secondary obstruction <20% in near perfect conditions will do twice as well as the 5″ APO in the same conditions — ie in the smallest detail to be potentially visible. It will probably cost little more than half as much. If the seeing is mediocre or poor there will be little difference in detail visible except in those occasional moments when clarity prevails for a moment or two — and the Newtonian wins again. The larger ‘scope will produce a significantly brighter image that will take much more magnification before it becomes unacceptably dim and uncomfortable to view.

Don’t get me wrong, refractors are beautiful telescopes inch for inch, but they are practically limited in aperture. (well they are aperture-limited by the depth of your pockets I guess). Aperture of the primary mirror/lens is the prime determiner of how much detail is potentially visible in a planetary image.

In poor, mediocre or average conditions a SCT of similar size to our Newtonian will perform about as well on planetary detail as the Newtonian. In very good conditions or excellent (rare) the Newtonian will produce a somewhat crisper image due to the much smaller secondary mirror used. It is a simple matter of physics due to the size of the secondary obstruction and the wave-nature of light. Increase the secondary mirror size and you push more light out of the Airy-disc and into the surrounding diffraction pattern. As Foghorn Leghorn said to the young chicken-hawk “Son yer can argue with me, but yer can’t argue with figures” — and that’s a fact, not an opinion!

Also, it is a simple fact of life that in a typical commercial SCT used with a diagonal, you need to get 5 optical surfaces right for it to work well. In a Newtonain there are only two.

If you are looking for a quality, visual-use, portable “APO killer” for an Eq6 mount, get yourself an 8″ f/7.5 Newtonian with a 25mm secondary. Longer focal length Newtonians are easier to collimate and much more forgiving of slight errors. Additionally, they are much easier to fabricate! Your eyes (and bank-balance) will thank you for a long time — it will flog the pants off any 4″ APO on any subject in the night-sky save perhaps ultra-wide field viewing. The image will be 4x brighter at a given magnification and will show twice as much detail in the right conditions.

Les D (Australia), from an online thread entitled; PLANETARY VIEWING ?? -aperature rules?or telescope type?

Unless your mirror is absolute and total trash, the reason is cool down, collimation, or seeing. Sounds like you took care of cool down and collimation so… Seeing.

Big scopes are able to resolve more, so they are subjectively more affected by poor seeing. I noticed this last night. I set up my 15″ next to so[me] nice Apo refractors, and stars looked better in their scopes. Seeing was exceptionally bad for me last night, stars were bloated little orbs over 150x, but they looked fine in the refractor. Peering at the moon, I didn’t see that shimmering you describe, but defocusing a star I could see very very fast upper air movement.

Now I know my mirror is not trash, it’s actually quite good and I’ve seen pinpoint stars at 300x in it and views of Jupiter that look like photographs. Last night, I couldn’t even see the GRS. So on nights of bad seeing, a small scope will be subjectively better because it isn’t big enough to resolve the poor seeing, at least not as well as a larger scope. That’s normal.

I[t] beat the pants of[f] the refractors on M13 though, and the Leo triplet, and M104, and M51… Shall I continue the list?

Brian Carter (Atlanta, Georgia), from an online thread entitled:Jupiter in my Dob vs Refractor?

Are those little apochromatic refractors really better than reflectors? They certainly have been advertised as such. In fact, refractor manufacturers have always alleged that reflectors are, well… just a little less than the ultimate – workable, useable, but really not first rate – images just a little sour. And in fact, many a view through a reflector confirms the sour image reputation. Views through refractors are invariably sharp and crisp, neat and gratifying to the eye. But are reflectors really a poor man’s telescope, a less than optimum instrument? As you might imagine, I don’t think so. And here is why I think not and why the “super little refractor” thing is just another load of advertising hype……….

While a Newtonian reflector of aperture and design proportions sufficient to function as a serious instrument for lunar and planetary observing is not going to be as readily portable as a small refractor or Schmidt Cassegrain or Maksutov instrument, such an instrument will optically match or out-perform all other forms of astronomical telescopes inch for inch of aperture in larger sizes. The problem is that such a Newtonian reflector requires slightly more care and consideration in use, but will be considerably less expensive to construct than any of the other telescope types. The point to emphasize here is that the Newtonian reflector is in no way a substandard instrument when compared to other compound reflecting optical systems or refractors. It is every inch the equal of these instruments, and, I believe, in many ways superior. Design the instrument well, construct it out of quality materials and with care, and fit it with quality optics. Give the instrument chance and it will absolutely amaze you.

Robert F. Royce (professional optician), from his article, Reflector vs. Refractor.

As early as 1972, the renowned British telescope maker E.J. Hysom conducted a careful series of experiments with mirrors of various diameters and thickness using a sensitive thermocouple. Hysom determined that a 30mm (1.2 inch) thick mirror cools at a rate of 3.3°C per hour, while a 76mm (1.8-inch) thick mirror cools at a rate of only 0.9°C per hour.
With the aid of a fan these rates could be increased by a factor of three.
Thomas Dobbins, from an online article entitled: The Recent Evolution of the Planetary Telescope: Part 2.

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.

My 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! Vainglorious eejits continue to bicker over and covet this new breed of ridiculously overpriced refractors with low dispersion glass for visual use; and with little or nothing to show for it. Life’s too short. Modest and marvellous in equal measure, Newtonians are my instruments of choice, based solely on performance, when I want to pursue either serious or casual observing. And I’ve earned the right to do so!

Mr. Hardglass.

 

Neil English is author of several books on amateur astronomy. His newest title (a largely historical work): Chronicling the Golden Age of Astronomy, will be published later this year.

 

 

Long Focus Redux: A Spell with the Orion SpaceProbe 3 Reflector.

The Orion SpaceProbe 3 altazimuth reflector in British racing green. In a word: awesome!

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Dedicated to Lars Filipsson

 

Tuesday December 5 2017

The Orion Spaceprobe 3 reflector package arrived in the early afternoon in perfect nick. It was purchased from amazon.co.uk deliberately so as to test whether such a company would deliver the product in good condition. The telescope was double boxed and each of the components were further packaged away safely in separate smaller boxes.  All items received looked fine.

The product arrived well packed with no damage.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The optical tube assembly was protected with bubble wrap.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The tripod had foam between the legs to prevent their movement during travel.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

All in, the instrument cost just over £70 delivered to my door. I could have opted for an even cheaper rendition of the ‘scope but I went with Orion USA because they have the telescope made to their own specifications, and that includes the addition of quality accessories; namely two good 1.25″ eyepieces; a 25mm and 10mm (probably modified achromats) with good antireflection coatings applied to their lens components, delivering powers of 28x and 70x, respectively.

Two superior quality oculars came with the Orion SpaceProbe 3.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

There were no junk Barlows with this package (a great relief compared with other entry level telescopes). I also received a collimation cap, a Philips screwdriver, a red dot EZ finder, an excellently written instruction manual and leaflet to enable me to download Starry Night software. The telescope also came with a one year limited warranty, so I could return it were I to find any of the components to be defective.

The telescope was easy to assemble and took just about 20 minutes of my time.

My first test was to see if the telescope delivered sharp images out of the box. A newcomer would be very disappointed if he/she found that it did not work as advertised. To my great relief (and joy too), the instrument delivered very sharp images with both eyepieces, so all was well.

One especially neat feature of the telescope was that the primary mirror came centre spotted, which greatly facilitates with accurate collimation. That was another reason I opted for the Orion model; some youtube presentations of other incarnations of the telescope did not appear to show this feature on the primary but carefully studying this video allowed me to glimpse this important feature, and I thereby reasoned that there would be a good chance of finding one on my model. My luck paid off.

Inserting a laser collimator into the eyepiece holder showed what my sneak peek observations confirmed; the telescope was quite well collimated in the factory and only needed slight tweaking of the primary and secondary mirrors (using the supplied screwdriver) before it was absolutely perfectly aligned. The entire exercise took just a minute or two and was easy to conduct.

The well written instruction manual has instructions on how you can tweak the collimation on the telescope using the screwdriver and collimation cap supplied with the ‘scope.

The telescope was found to be nearly perfectly collimated, as evidenced by the position of the red dot near the centre of the mirror.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The fact that the instrument was well collimated didn’t actually surprise me, as the system has a larger relative aperture. At f/9.2, good collimation ought to be easily held.

Fine collimation is rendered very easy using the protruding screws on the primary mirror cell and the supplied Philips screwdriver.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

I elected to use the telescope using my own 6 x 30mm achromatic finder as well as not engaging the altitude bevel. Simply adjusting the altitude tension on the knobs on the mount head was good enough to provide just the right amount of tension.  I did check to see if both of these worked, by the way; and they did as advertised. I also chose not to attach the accessory tray, as this would enable me to collapse the tripod at a moment’s notice and store it away when not in use.

The telescope atop its altazimuth mount is very lightweight and can easily be lifted with three fingers. I moved the instrument to my back garden and gave it a few minutes to acclimate more fully in the cool, overcast daylight. Although lightweight, the aluminium tripod is quite strong and stable; a good match to the featherlight mass of this telescope. Motions in azimuth and altitude were smooth and hassle free, even using higher powers. Mechanically, I was very impressed at how well the instrument was shaping up.

The simple rack & pinion focuser  operated smoothly and can be adjusted so as to tighten or loosen it as desired. Applying the laser test showed that collimation remained stationary throughout its travel; neat!

The telescope has a good rack & pinion focuser that operates smoothly and accommodates 1.25″ eyepieces.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

As previously stated, I chose not to use the supplied EZ finder as they are pretty useless for anything dimmer than 1st or 2nd magnitude stars. I quickly found a 6 x 30mm unit that attached easily to the telescope and which did not clash too much with the colour scheme of the rest of the instrument. This is a much better option going forward, as it allows me to aim in on much fainter stars from my dark, rural sky.

Close up of the finder I mated to the ‘scope; note the matching colour and texture of the finder bracket with the focuser and rim of the optical tube assembly. Schmokin’ !

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Preliminary Optical Testing

The supplied oculars delivered extremely sharp views of distant trees at 28x and 70x. Contrast was excellent. I decided to push the telescope using the supplied 10mm ocular and a 2.25x Barlow. The result was truly astounding! But to be specific; the image remained razor sharp at this power (that’s 158x for your information) across the entire field. To be honest, I was a bit shocked and called a few of my neighbours to have a look. They agreed with me; the images were unreasonably excellent!

But I went even further; I attached my 7.5mm Parks Gold eyepiece to the 2.25x Barlow which increased the power still more to 210x. Amazingly, though the image was fast running out of light, owing to its small aperture, it was still tack sharp and full of detail!

This telescope appears to have astoundingly good optics for the very modest price I paid to acquire it!

This agrees with the findings of Lars Filipsson et al, who kindly alerted me to this ‘scope, as well as those of the American gentlemen on the youtube presentation highligted above. It also jibes well with the findings of the veteran observer(a Newtonian specialist) and Sky & Telescope reviewer, Gary Seronik, who gave the same instrument a 4 star rating. Former S & T associate editor, Tony Flanders, also liked the telescope.

Based on this preliminary testing; I can confidently recommend this telescope to beginners on a tight budget. Here’s a link to the amazon site I purchased it from.

How did they do it? What’s going on?

A perfectly shaped 76mm spherical mirror forms the heart of this instrument.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Nae chance of starlight or moonlight this evening; very cloudy unfortunately

Wednesday December 6 2017

It is noteworthy that in his field tests, Seronik rated the SpaceProbe 3 reflector above that of a classic 70mm refractor. Indeed, concerning the former, he wrote that it was just a “nice telescope. It provided sharp images and was a joy to use.” What is more, only the larger aperture 4.5″ reflectors rated higher than the little long focus 3 inch reflector. As explained in a previous post, a mirror with a parabolic shape is the ideal form for a Newtonian, as it effectively negates the effects of spherical aberration. But for small mirrors (less than 5 inches or so), a spherical mirror can generate good images if the focal length is made sufficiently long. We need not enter into a technical consideration of these tolerances only to say that at f/9.2, the differences between a parabolic and spherical mirror are negligible, especially for a 3 inch aperture.

Of course, there are other advantages of long focal length systems. All aberrations get smaller as the f ratio increases, allowing even inexpensive eyepieces to work well. Traditional aberrations considered in Newtonians, such as coma and field curvature, are vastly reduced at f/9.2 compared with say, a comparable f/4 system. That’s why inexpensive eyepieces won’t work well in the f/4 Starblast but will perform admirably at f/9.2. Needless to say, I’m very much looking forward to testing this telescope under the stars but that can’t happen until conditions improve.

With a focal length of 700mm, the instrument can deliver pleasingly wide fields with inexpensive eyepieces of long focal length. One obvous choice is my 32mm Plossl, which should serve up a power of 22x in a 2.3 degree field. That’s perfectly adequate for the vast majority of larger deep sky objects, so the instrument should give very pretty views during low power sweeps.

Thursday, December 7 2017

The Spaceprobe 3 telescope set up for more daylight tests.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

After a very wet and cloudy day yesterday, I was able to resume more daylight testing of the SpaceProbe 3 telescope this afternoon in much colder and brighter conditions.

I have been enjoying the two eyepieces that came with the instrument, both of which are labelled as “Explorer II” oculars. Conducting more tests at high powers, I can reaffirm that the optical quality of the telescope is excellent; noticeably sharper and brighter than a typical long focus 60mm achromat or shorter focus ED apochromat of the same aperture( 60mm).

The supplied oculars are very good but could do with a Barlow lens to extend powers when required.

 

 

 

 

Because the maximum magnification yielded by the supplied 10mm ocular is only 70x, I would recommend that users consider the purchase of a decent Barlow lens to increase the range of magnifications one can achieve in the field. For example, a 2x Barlow inserted ahead of the eyepiece(see the above image) will boost the power to 140x when used with the 10mm eyepiece and a 3x Barlow will give 210x. The higher powers, of which this small telescope appears eminently capable of, will come in handy when viewing the Moon, planets and close double stars. A 2x Barlow will also boost the power of the 25mm Explorer II eyepiece to 56x.  I would avoid the cheapest models though; try to go with a multicoated Barlow that will cost £30 or more new. Alternatively, you can always search the buy/sell websites in your country where you can pick up decent second hand models for not a lot of money.

With the tripod fully extended, the SpaceProbe 3 reflector is raised quite a bit off the ground allowing comfortable standing viewing for an adult, but the legs can be collapsed to allow a child or a seated adult easy access to the eyepiece. Newtonian reflectors are much more comfortable to observe with compared with refractors or Maks, especially when viewing objects at greater altitude above the horizon. And greater comfort means that one can engage better with the images garnered by the instrument so that they can be studied for longer.

Time: 21:45 to 22:15 UT

Seeing: III, clouds clearing gradually leaving a clear sky, more sleet and snow showers due overnight, waning gibbous Moon rising in the east.

Temperature: 0C

I enjoyed my first light under a dark sky with the Orion SpaceProbe 3 altazimuth reflector and it continues to impress. I inserted my lowest power ocular (a 32mm Plossl) and aimed it at Capella now high up in the eastern sky. The telescope focused this creamy white star down to a tiny, brilliant pinpoint. The first thing I noticed was how the astigmatism that is present in my observing eye did not manifest itself as it does with my faster reflectors (with focal ratios of 5 and 6) using the same eyepiece. I did not need my glasses to correct it. Moving the star from the centre to the edge of the field I was deeply impressed with how the focused stellar image did not become distorted. It reminded me very much of the views I grew fond of in my classical refractors. F/9.2 is a great place to be in a reflector!

From there, I moved to the Pleiades, now becoming more prominent in the sky as the hazy cloud dissipated. The image was just charming! A host of blue white fireflies glistening in the frosty winter sky. Increasing the power to 70x using the 10mm Explorer II eyepiece supplied with the instrument, I examined the 70x images of Albireo, now low in the west. The Airy disks were round and rich in natural colour; golden and blue. From there, I visited Almach much higher up and once again the lovely colour contrast pair was well resolved. Lifting the telescope with one hand, I moved from the back garden on to the front lawn and focused in on Castor A and B; a beautiful sight in this little telescope. I then tested the high power perfomance of the telescope by coupling my 2.25x Baader shorty Barlow to the 10mm Explorer II eyepiece delivering 158x. Both the A and B components focused down to hard, round Airy disks. I could not see any distortions in the image. Just beautiful round disks surrounded by a faint diffraction ring. The image remained equally sharp at 210x when I exchanged the 10mm with my Parks Gold 7.5mm.

Though the tlescope on its mount is very lightweight, I was still able to track this star system quite easily at the highest powers. I’m learning how to adjust the tension in the altitude axis so as to keep the system in the field of view for prolonged periods of time as I do with my other telescopes on their respective mounts.

So far, so very good! Now waiting for the Moon to rise higher in the sky; pretty excited with the prospect of seeing our natural satellite in this fine little telescope.

Friday December 8 2017

Time: 00:30UT

Just got in from a spell of Moon gazing with the SpaceProbe 3. I can confirm what the American gentleman said about this telescope in his youtube video clip and associated review; it’s an awesome lunar telescope! The 10mm Explorer II eyepiece with 2.25x Barlow produced a wonderfully sharp image of the lunar regolith at 158x. I pushed it some more using my Parks Gold 7.5mm (so 210X) and the image remained very sharp and with excellent contrast!

Isn’t modern mass produced technology wonderful!

Time: 12:30UT

I ventured outdoors again this afternoon to enjoy the high power views of the SpaceProbe 3 reflector. On these short and cold days, sunlight is a precious commodity and I especially savour the images of the tree tops that catch the rays of a feeble Sun. 210x is worth seeing in this telescope!

Based on what I’ve witnessed so far, there is another group of amateurs that would greatly benefit from experiencing this telescope; those that profess ‘advanced’ telescope knowledge and/or insist on procuring gear of the highest quality. For a fraction of the cost of one high end eyepiece, you can experience for yourself the virtues of this little telescope. I dare say, it would do you the world of good to do so!

We’re away for another short vacation this weekend. Hope to resume my observations with the Orion reflector upon my return.

Sunday December 10 2017

Tayside panoroma on an idyllic winter day. Shot taken from outside our hotel, shortly before midday, local time. The picturesque Kingdom of Fife lies just across the water.

After a great weekend of leisure and Christmas shopping in the city of Dundee in the northeast of Scotland, we arrived home at dusk (about 4pm local time) and after setting the fire, I ventured out on what proved to be the coldest night of the year so far to conduct more tests with the Orion SpaceProbe 3 reflector.

TIme: 16:40 UT

Temperature: −7C

Seeing: III, a tad below average, despite excellent transparency and a cloudless sky.

Left: the 130P Newtonian and right, the little 3 inch Orion SpaceProbe spying Epsilon Lyrae.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Fielding both my 130P and SpaceProbe 3, I turned them on Epsilon Lyrae and charged them with a power of about 150x (10mm Explorer II ocular and 2.25x Baader shorty Barlow. Both telescopes resolved the four stars of this famous test multiple star system. The split was much more convincing in the larger 130P, as expected, but it was also well resolved in the 76mm reflector.

From there, I swung the telescopes eastward into Cassiopeia and centred Iota in the instruments. Again, I was rewarded with good results; the little Orion SpaceProbe 3 did manage to resolve all three components at the same magnifications but, as I expected, the image was brighter and more effectively resolved by the larger 130P telescope.

Time: 23:00 UT to 23:40UT

Temperature: −6C

With the Pleiades near the meridian by now, I tested the 32mm Plossl out in the same instruments. The 130P, with its shorter focal length, served up the larger true field (2.5 degrees) but the SpaceProbe also framed the entire cluster well using the same eyepiece (the Pleiades subtends a true field of about 2 angular degrees), albeit in a slightly smaller field of view. This time, I looked for vignetting at the outer edge of the field in the 76mm Orion reflector and felt that although a small amount was present at the extremities it wasn’t a big deal. The telescope certainly provides a generous maximum true field of view for beginners and more experienced individuals too.

By lowering the back leg of the Orion tripod, greater altitudes can be reached.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

By now, the Double Cluster (Caldwell 14) in Perseus was nearly overhead. Others have reported that the little 3 inch reflector cannot quite reach the zenith because the tube bumps into the tripod. Although this is true, I did find that lowering one of the legs of the tripod allowed me to increase the pointing altitude of the telescope a wee bit more, and I was finally able to view these magnificent objects using both the 32mm Plossl and the supplied 25mm Explorer II ocular. The view in both eyepieces was very beautiful in the little telescope but I did find the latter to be more compelling, as it delivered the slightly higher power and framed the clusters that little bit better.

Left, my 80mm f/5 achromat and right, the Orion SpaceProbe 3 trained on Rigel, now near the meridian.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Next I fielded my 80mm f/5 achromatic against the Orion SpaceProbe 3, comparing the view of Rigel (Beta Orionis) now approaching the meridian. Though there was quite a bit of turbulence at this lower altitude, I was able to just resolve the faint companion at 166x in the ShortTube 80 using my 2.4mm HR eyepiece and at 158x (10mm Explorer II and 2.25x Baader shorty Barlow) in the 76mm reflector. The 80mm refractor image was that little bit brighter though, which didn’t present as too unexpected.

These results show that the inexpensive Orion telescope can resolve higher resolution systems when pushed to higher powers. Adequate cooling and careful collimation are always your friends in this endeavour.

Monday December 11 2017

A snow covered Ben Lomond, as seen on the morning of December 11, just a few miles from my home.

Time: 12:50UT

The icy weather continues.

I conducted a daylight test with the 32mm Plossl on the SpaceProbe 3. Aiming at some trees in the distance (150 yards) in bright, winter sunshne, the eyepiece gave a very nice, sharp, flat field. I did not notice any dimming at the edges of the field.

The rather thick vanes holding the secondary mirror in place.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The secondary is held in place by three vanes that are rather thicker than in my other Newtonians. This gives rise to a more prominent diffraction pattern around high magnification stellar images. Although I find this perfectly acceptable for an entry level telescope, it could have been designed better. Such a small secondary mirror could easily be supported by thinner vanes.

One other issue I have with the telescope is that there is a clip on the right edge of the secondary mirror (as you look down into the eyepiece holder), which appears to shave off a small amount of light that could come to the telescope (see below). I have no idea why they used such a clip but, again,  it’s something I can live with.

The right side of the secondary mirror (seen here in this off centre image) has a clip which does cut off a small amount of light reaching the eyepiece.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

As mentioned previously, the two eyepieces that come with the telescope are of good quality. I believe they are two of a larger set of Explorer II oculars which originally came in focal lengths of 6mm, 10mm, 13mm, 17mm, 20mm and 25mm. I found a short review of them here. It makes interesting reading. Both the 25mm and the 10mm are apparently Kellners, while the rest are Plossls.

Time: 23:15 to 23:45 UT

Seeing: II, an improvement over last night, remaining clear and very cold.

Temperature: −3C

My adventures with the little long focus reflector continue apace. Tonight, I set the telescope up to have a look at some favourite seasonal deep sky objects. I began with M35 in northern Gemini, which looked like a storm of faint stars haphazardly strewn across the face of my wonderful 25mm Explorer eyepiece. I enjoyed a spellbinding tour of the Sword Handle of Orion, and was particularly impressed by the images served up of the Great Nebula in Orion (M42 & M43) using both the 25mm and 10mm oculars. The companion to Rigel was beautifully resolved in the improved seeing at 93x using my 7.5mm Parks Gold.

Beta Monocerotis as seen through the 3″ f/9.2 reflector at 210x.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

When I turned the telescope on Eta Orionis, I cranked the power up to 210x using the 10mm Explorer II Kellner and 2.25x Baader shorty Barlow, focused carefully, and was greeted by two kissing Airy disks; a very good result indeed for such a modest optical accoutrement! But the corker for me this evening was the sight of Beta Monocerotis triple system. At 210x the view was awesome! This telescope produces wonderful images of very delicate targets and with excellent contrast. No wonder seasoned observers and beginners alike are drawn to its considerable charms.

Wednesday December 13 2017

I have spoken before of the very high contrast of the images generated by the oculars that came with the Orion SpaceProbe 3. On the evening of Monday December 11, I was comparing the view of the Sword Handle of Orion seen with this 3″ reflector with that garnered by my 80mm f/5 ShortTube refractor. The SpaceProbe 3 had the 25mm Explorer II eyepiece and the 80mm refractor was used with the Mark III Baader Hyperion zoom eyepiece, which was set to approximately 14mm focal length, so as to show the region at the same magnification as the reflecting telescope. What I noticed but did not report at the time was that the contrast of the image in the Spaceprobe was much better than that served up by the Baader zoom in the 80mm f/5 glass. The difference was very striking; the sky was much darker and the nebulosity within the M42/3 complex more strkingly presented in the reflector image. I noted this result as very odd, as one would expect the refractor to have the better contrast. So last night, I dodged the showery weather and ventured out again to conduct more experiments.

Between 23:00 to 23:45 UT on Tuesday December 12, I decided to deploy my 130P reflector to observe the Orion Sword Handle and included the two Explorer II eyepieces  together with the Baader zoom  to compare and contrast the images. Since the 25mm Explorer II eyepiece gives a magnification of 28x, I first compared the view in the 130mm reflector using this eyepiece and the zoom set to the same magnifiation (so setting the zoom to near the lowest poewer setting at 23 mm). The result was remarkable: the 25mm Explorer II eyepiece produced a much more contrasty image than the zoom did, despite showing more in the way of off axis aberrations!

Switching then to the 10mm Explorer II ocular which delivers 65x in the 130P, I moved the zoom to near the 10mm setting (so delivering the same 65x power), I again compared the images. The 10mm Explorer II eyepiece produced a much more contrasted image in terms of sky background and how well the M42/3 nebulosity stood out in comparison with the Baader zoom!  Indeed the view through the 10mm Exploer II eyepiece on axis was truly excellent! What’s going on here?

My working hypothesis is that the number of lens elements in the eyepieces had a bearing on this very striking result. The Explorer II eyepieces are simple, 3−element Kellners ( modified achromats), while the zoom has 7 elements. The minimalist design of the latter oculars produced a dramatic difference (to my eye) in terms of how much contrast the images were producing at the same magnification. What an interesting finding! I shall conduct further experiments as soon as conditions allow.

Are minimalist eyepieces the way to go?

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

A quick google search on this topic revealed some interesting results. Check out what the OP says here about the same eyepieces, together with the various responses.

Time: 22:45 UT to 23:40 UT

Temperature: 0.5 C

Seeing: II, very good between snow showers. Windy at times, sky noticeably brighter.

Classic 3 incher.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

If it wasnae fur yer wellies, where would ye be?

 

Got a fair good spell later in the evening after a couple of snow showers. I was comparing the view through the Orion Explorer II Kellners and my Baader zoom. Turning on two targets; M42/3 and the Pleiades, I studied the images in the 25mm Exlorer II and compared them to the 24mm setting on the Baader zoom. The result was quite compelling: the simple Kellner was noticeably more contrasty than the zoom set to 24mm. The field of view was also larger in the Explorer eyepiece too; and that’s consistent with what others have said; it gives a nice 50 degree field, quite comparable to a Plossl. In comparison, the Baader is more like 40 degrees at this setting. The 25mm Explorer produced an absolutely draw dropping view of the Pleiades high up in the south, with pinpoint stars set against a jet black sky. Again, it reminded me of the views I enjoyed through my classical refractors, using simple eyepieces. The Explorer II 25mm was made to be used with an instrument such as this! It just rocks with the small aperture and long native focal length.

The same tests carried out on the 10mm Explorer II eyepiece (and the appropriate setting of the zoom) produced slightly less striking differences but they were there nonetheless. What is more, the larger field of the zoom complicates the situation at this focal length.

I ended the evening looking at the same objects in both the 3″ SpaceProbe and my handy 80mm f/5 achromat. Again, I can report that the 25mm Kellner produced a darker sky background than the zoom set to 24mm in the refractor. Light grasp in both instruments was quite comparable though, with the edge going to the 80mm glass.

So, the little SpaceProbe 3 Altaz revealed a weakness in my trusty Baader zoom eyepiece. Though very satisfying, it does not offer up the very best contrast when it comes to eyepieces. That being said, I would never dream of parting with it. It’s still very good and comes quite close to what you’d get with a quality, simpler, fixed focal length ocular. Its zoomability keeps you reaching out for it.

Friday, December 15 2017

Small Newtonians in the snow.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Because I wish to keep this little gem of a telescope( what would the point in selling it be?), I have bestowed the name Oona( a ‘she’) upon it.That’s what I’ll call the SpaceProbe 3 any more.

 

Oona: a ‘scope that offers delightful images.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

To sum up, the Orion SpaceProbe 3 represents tremendous value for money. It’s just a very honest ‘scope, just as ‘Rocket Roberts’ stated in his review. By that, I mean that you get exactly what it says on the tin. It’s easy to deploy and use, even if you live in an apartment with limited space. It is very lightweight so it can be carried around very easily, yet strong enough to allow you to follow objects even at higher powers. It gives very pleasing views of deep sky targets, as well as solar system objects (I personally cannot wait to aim this ‘scope at Jupiter in the new year) and can be enjoyed by all the family. I highly recommend this telescope to a budding young stargazer or more experienced observers wishing to enjoy the considerabe optical benefits of using an old school, long focus Newtonian.

This is where this review ends. My sincere thanks again to Lars Filippson for recommending this telescope for testing.

Thanks for reading.

 

Neil English is the author of several books on amateur telescopes. If you like this work and wish the author to continue, please consider purchasing one of his books.

 

Postscriptum: Former Sky & Telescope Contributing Editor, Gary Seronik, who is a Newtonian specialist, wrote a wonderful article on his website on this little 3″ f/9.2 Tasco reflector. You can read what he says about it here.

 

De Fideli.

New Adventures with the SkyWatcher 130P

Think inexpensive telescopes can’t deliver top class perfromance? Think again!

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Dedicated to Rob Nurse

Introduction

One of the most egregious myths promulgated by contemporary telescope forum culture is that one has to splash out large sums of money for a high quality telescope. This is especially the case with refractor—obsessed enthusiasts who have reduced the hobby to an activity more related to pornography than anything else. Serving more as ‘phallic symbols’ than tools, they spend countless hours ‘drooling’ like animals over instruments with tiny apertures, and revealing little or nothing of any substance or lasting value. Over the last two decades their designers have systematically robbed an entire generation of amateurs with their ridiculously priced ‘peashooters’ and all for the sake of better colour correction. Yet all the while, the reflecting telescope was systematically ignored or down played; that is, until this author blew the whistle.

As a former victim of this dead–end cult, I came to realise through experience that despite owning and using a suite of high-end refractors (think Takahashi, Televue, Meade, William Optics etc), inexpensive mass—produced Newtonian telescopes from the Far East were not only superior to the latter, but were easier and more comfortable to use. In a previous blog, I brought people’s attention to the SkyWatcher Heritage 130P flextube Dobsonian that revealed its superiority to much more expensive telescopes (in this case a high quality 90mm ED apochromat) on all targets. The key to providing these high quality views involved careful collimation and adequate cooling.

These thoughts came flooding back to me after this author acquired a used SkyWatcher 130P optical tube assembly for the princely sum of £65 plus £10 delivery. Once it arrived I was able to collimate the instrument and test it out for its high magnification performance on good daylight targets, where it was found to deliver excellent images with no image breakdown at powers up to and in excess of 270x diameters. Such a telescope had a well figured 130mm (5.1 inch) f/5 parabolic primary mirror with a secondary mirror obstruction of just 37mm (so a modest 28 per cent), which is significantly smaller than their catadioptric counterparts, and so should enable one to see finer, low contrast details on the Moon and planets.

Now, I wouldn’t expect you to take my word for all of this. That’s why the reader will also take note of reviews carried out on the same instrument dating back over a decade ago. In this evaluation, for example, the highly experienced reviewer reported no image breakdown when the telescope was pushed to magnifications of 250x. This also resonates with the findings of this in depth review made by another experienced observer a few years back. Failing these, the reader should also take note of comments from a varety of other users here and here. In addition, in this short thread, posted in the Cloudy Nights refractor forum, the tester of essentially the same optics (the Astronomy Without Borders, One Sky Newtonian) reported that it was quite close in performance to a 120mm ED refractor costing many times more.

Beyond Symbolism

In previous work, I noted that a properly—tuned Skywatcher Heritage 130P proved to be a better double star splitter than a 90mm apochromat. In the same report, this author noted how this modest telescope was also capbale of rendering a much more convincing split of tight systems such as Pi Aquilae than a previously owned and thoroughly tested Skylight 4″ f/15 classical refractor. This should not surprise anyone; when conditions are good and the optics are properly aligned, aperture wins.

That said, this new blog will not concern the optics in the 130P pictured above. Rather, what I wish to write about here concerns the consequences of transplanting my modified Heritage 130P optics into the closed tube of the 130P. How would they behave?

The reader will recall that the primary mirror of the Heritage 130P was left unchanged as I judged it as perfectly adequate. But what I did do was to get it recoated with the finest coatings money could buy (still a modest investment) and in this capacity sent the mirrors down to Orion Optics UK to have them treated with their proprietary HiLux caotings for increased reflectivity, reduced scattter and optimal durability. I also replaced the existing flat with one of slightly smaller size (35mm minor axis diameter giving a linear obstruction of just 27 per cent) and higher quality (read optically flatter, but economically so). But how easy was it to house those optics in the new tube? As it turned out; it was quite straight forward!

The primary mirror transplant was the easiest to perform, involving a simple swap of the existing mirror of the 130P (also centre spotted!) with the HiLux coated mirror from the Heritage.

The primary mirror transplant: the HiLux treated primary from the Heritage 130P was placed in the 130P mirror cell (pictured at top right).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The secondary mirror swap was a little more challenging. In short, they were designed differently, so necessitating the removal of the existing flat on the 130P secondary and gluing on the new flat derived from the Heritage 130P. In all, it took about half an hour of open heart surgery.

Finally, to ‘turbo charge’ the new closed—tube optics, I borrowed some Bob’s knobs from my 8 inch Newtonian and placed them on both the primary and secondary mounting cells as indicated below.

The new flat with Bob Knob’s inserted. Note the very modest secondary obstruction.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

And the primary cell….Note the back plate has been removed.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Justifying the Transplant

While the Heritage 130P flextube telescope is ideal for airline travel (check out SteveG’s report on how he brought it to Hawaii while on vacation) and for vacations within the UK, I wanted to be able to mount the same optics in a more stable tube, especially since it would be used regulalrly for high resolution work over winter at my home. After having extensively used the helical focuser on the Heritage tube, moving to a proper rack and pinion was a huge step up in luxury. Have you any idea of how much easier it is to hold precise collimation with this new focuser?  I can assure you that such an upgrade is nothing short of pure, unadulterated joy!

The simple rack and pinion focuser is a wonderful luxury I have greatly appreciated.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Rummaging through my old box of tricks, I retrieved a colour matched 6 x 30mm finder which is a huge improvement over the RDF supplied with the Heritage 130P. RDFs are only adequate if you wish to locate the brightest stars. With the 6 x 30mm finder, I will be able to pinpoint much fainter targets to increase the efficiency of my observations. All in all, Plotina has a new and more stable winter coat.

The upgraded finder for Plotina, raised from the author’s box of tricks

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Proof of Concept: Reports from the Field

Plotina belongs to a long and distinguished family of true and original apochromats. It’s fast f/5 relative aperture enables me to go from 20x and a very generous 2.5 degree field to powers in excess of over 300x for high resolution work, particularly in my chosen area of interest; double stars. In many previous blogs, I have also stated how good this little telescope was on the Moon and planets. Here I wish to continue her legacy by fielding my beautiful little closed—tube Newtonian under the starry heaven………

Seeking starlight.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Date: November 4 2017

Time: 20:00 to 20:45 UT

Seeing: very good (II), frequent squally showers moving in from west, some good clear spells. Full Moon in the east.

Temperature: +3C

Targets:

Polaris: Excellent star test. Intra and extrafocal images almost identical at 200x. In focus image revealed the faint, wide companion even in the bright moonlight.

Epsilon 1 & 2 Lyrae: textbook perfect split at 183x using Baader zoom at the 8mm setting coupled to a 2.25x shorty Barlow. Beautiful and faithful colour rendition of the four components.

Delta Cygni: A decidedly more difficult target, but once again easily handled and beautifully rendered at 244x using a 6mm Baader orthoscopic and 2.25x Barlow. A gorgeous, brilliant white Airy disk with a faint steely grey companion well separated from the primary.

Almach (Gamma Andromedae): not really a test but a sight for sore eyes in this fine little telescope at 183x.Lovely contrast.

Iota Cassiopeiae: the highlight for me this evening, now not far from the zenith. I charged the instrument with a 2.4 mm Vixen HR ocular delivering 271x. Focusing was very easy to achieve and I was delighted to see it deliver a bright and perfectly formed image of all three components in their true colours.

A quick look at the full Moon at 20x using my trusty 32mm Plossl revealed a razor sharp image rich in contrast and in a relatively enormous field.

Comments: To say that I’m pleased with tonight’s results would be an understatement! I am beside myself! The Vixen Porta II is a good mount for this telescope with its smooth slow motion controls on both axes, and with the eyepiece at a very comfortable standing height for me (I’m a six footer). All tested oculars come to a precise focus easily with the rack and pinion.

23:05 UT  to 23:35 UT ventured out again to test a few other tricky systems

Rigel: Easy at 81x despite its low altitude (still a wee while from culmination)

Eta Orionis; A corker at 243x! Very tight pair split with this marvellous 5.1″ speculum at a suboptimal altitude.

Theta Aurigae: Now favourably placed high in the eastern sky. Easy split at 183x

Date: November  5  2017

Missed an early session this evening, as we ventured out for bonfire night. Anger nonetheless kindled against those supposedly ‘experienced’ peers who left this amazing, economical telescope in the dust. Why did you not test it? Too busy drooling were you? Why did you not advise your peers about it?  How many amateurs might benefit from using this instrument?

You really need to examine yourself!

Shame on you!

Time: 21:45 UT to 22:30UT

Temperature: –2C

Seeing: II, remaining very good, very cold and clear, bright Moon in the east.

Iota Cassiopeiae: Easily resolved at 183x but better seen at 243x

Theta Aurigae: Observed once again this evening. Companion beautifully resolved from primary at 183x

Pushed the telescope hard on the waning gibbous Moon this evening. The telescope delivered wonderful images at powers from 20x to 325x! No image breakdown recorded at any of these powers. Wonderful images delivered in these sub–zero temperatures.

Comments: Lambda Cygni (0.9″) is now past its best and slowly sinking into the western sky, but I will attempt 52 Orionis (1.02″) and 36 Andromedae (1.14″) over this coming winter. I cannot for the life of me see why Plotina cannot resolve these systems under good conditons. Can you?

Plotina: a great blessing!

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Date: November 6 2017

More Justifications

Having a proper finder is a wonderful upgrade to the RDF supllied with the telescope. As stated previously, RDFs are only useful with the brightest stars and often, in colder conditions especially, the battery ceases to deliver its power rendering such a device useless. What is more, as a guy who likes to do all his observing without electronic appendages, fitting a traditional finder to this small Newtonian made a great deal of sense. When properly aligned it’s possible to centre objects, even at high magnification, increasing the efficiency of my observing sessions with this telescope.

Of course, one of the great joys of using this f/5 Newtonan system is the substantial increase in light gathering power it delivers over other other telescopic designs. Actually, it’s an enormous increase over a typical, small grab ‘n’ go refractor or Mak and will make your ‘quick look’ or grab ‘n’ go excursions far more rewarding than using an 80 to 100mm refractor, say.  F/5 is not so fast that one requires a coma corrector or some such and the field of view with a modest 32mm Plossl is quite well corrected across the majority of the expansive, 2.5 degree true field. One thing is certain; this telescope will be an absolute ball to use in the exploration of the winter deep sky.

Having a new winter coat avoids the need to fit a makeshift light shroud to the upper tube assembly, such as is the case with the Heritage 130P/ One Sky Newtonian. This affords a greater degree of protection against dew and stray light combined.  The increase in mass is negligible too; you can pick up the ‘scope with one hand or carry it under your shoulders even over a considerable distance.

As I noted with the Heritage 130P, quick acclimation is eminently possible with this telescope and my observations thus far made with the closed tube 130P give me little cause to think that its cooling off time will be substantially increased. 15 minutes is probably all you need, so even the laziest of you readers can get to work on the sky quickly and easily.

As described previously, I use a simple, inexpensive laser collimator to get quick and accurate alignment of the optical train. I consider the laser collimator a great improvement over the traditional  ‘collimating eyepiece.’ My high magnification tests conducted thus far show that the more stable housing of the optics in the 130P maintains this collimation significantly better, so there is far less anxiety involved in moving the telescope about.

One of the greatest (and largely unsung) assets Newtonians have pertains to their ability to be collimated rapidly. I’ve lost count of the number of stories I’ve read of folk who accidently whack their refractor or Mak tubes off a wall or door or some such and then worry that the optics may have gone out of alignment. For a Mak, the issue can be resolved at home, but not very easily. For a refractor, you’ll likely have to send it off to some specialist for proper realignment of the lens elements; and at an additional cost to you. All of this, of course, is superfluous to the man who learns to collimate his Newtonian. You can bump it off any wall you like and still have the reassurance that it will be working optimally in a matter of minutes.

In this capacity, Newtonians are the ultimate, low stress telescope.

The weather has nose dived in the last twelve hours back to mild, wet and cloudy. Time to take a break from this blog and return again when conditions permit more testing.

Me super duper bazuka…. .ken.

 

 

 

Toodleoo the noo.

Date: November 7 2017

Time: 22:11 UT

Seeing: I to II, excellent, good transparency, waning gibbous Moon, not too overwhelming (yet).

Temperature: 0.5C

While some of you were drooling on the fora, I was busy finding 36 Andromedae while the Moon was still low and monitored it at low power until it crossed the meridian at 22:11 UT or thereabouts. Charging the 130mm f/5 Newtonian with a 2.4mm HR ocular delivering 271x I can report a fine split of this system. Both stars separated by a sliver of dark sky and distinctly yellow in colour. The view was even more compelling at 325x. Perfect Airy disks! This is a magnitude 6/6.5 pair and the separation is 1.1″.

This telescope rocks!

Let goodwill and common sense prevail!

As always, I would encourage others to see if they can split this system with a 5 inch Newtonian reflector. Make sure your optics are well collimated and the instrument fully acclimated (you don’t need a fan either). You’ll be very surprised what you will see under good conditions!

As you can gather, I have dedicated this blog to Rob Nurse, who has started a friendly correspondence with me. I learned that back in the early to mid 1990s, Rob employed a little Tal 110mm f/7.3 to divine some pretty tight doubles using this reflector and has been following my work. Below is just one page of some of his results (used with permission). This is more evidence that well made Newtonians are excellent double star telescopes.

Rob’s list of systems visited with the Tal 110mm f/7.3

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

I hope you can see that he managed to split pairs down to about 1.3″ and his success was better the higher in the sky these pairs were situated. I suspect that he was wasn’t trying particularly hard to push the instrument though!

We need to keep working hard to root out the evils in this hobby, so feel free to help out if you can.

Date: November 8 2017

Last night was very exciting but I had to cut it short. 36 Andromedae was not a particularly difficult system for this telescope. For the record, it’s very close to the Dawes limit for a 4 inch unobstructed aperture. But in the right hands, the 130P is capable of doing significantly better than the finest 4 inch refractor money can buy. If you think otherwise, you’re simply deluded. Like I said before, I once drooled over a very fine 4″ inch f/15 refractor that set me back a small fortune. Yet this little reflector in my possession can outperform it; and I only needed to do some simple tests to affirm this. And no amount of justifying can change that fact.

For me, the reflecting telescope has been an instrument of liberation. Isaac Newton( 1642—1727), arguably the greatest scientific genius ever to have entered the human arena, invented this marvellous telescope. I think this was meant to be. But I hope you too can learn something from the hard lessons I have learned. The beauty of the Lord’s created Universe is not to be enjoyed only by an exclusive few. It ought be enjoyed by everyone. And the Lord has made this technology available to all at relatively little cost through the reflecting telescope. Pride has died; gratitude is born (sic gratia non superbia).

52 Orionis is just beyond the capabilities of a 4 inch aperture but should be quite doable with the 130P. I will have to wait for another good night to ascertain this.

Rob was also kind enough to provide a short list of other systems that will be interesting for those with small reflectors to visit over the course of the seasons. Some of these entries are dated but it would be fun to visit them nonetheless to see how they’ve changed over the years.

More tricky pairs to visit courtesy of Rob Nurse.

 

I’m blessed by having more quality eyepieces than you can shake a stick at but you don’t need to have the finest collection of ultrashort focal length oculars to boost the power in a short focus reflector. By far the most economical way forward is to invest in some Barlow lenses that can boost the power of the eyepieces that you may have in your possession.  For example, the Baader 6mm classic orthoscopic yields 325x with a 3x shorty Barlow and 243x with an economical 2.25x Barlow. My excellent Parks Gold 7.5mm ocular is also a great choice when coupled to a 3x Barlow yielding 260x. You can also get good results by Barlowing a medium focal length Plossl (a 9mm is a good choice).

A few decent eyepieces and some Barlow lenses can give you the magnification boost you need to get at tight pairs.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Date: November 9 2017

Faster, Cheaper, Better

Two small, portable telescopes; on the left and in the background, the 130P Newtonian and on the right and in the foreground, a 90mm f/5.5 Apo refractor. Two fine grab ‘n’ go telescopes but one clear and unambiguous winner.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

If you’re thinking ‘phallically,’ then you’ll likely say the 90mm refractor is better; afterall, it has a smoothly gliding extendable dewshield and a super ‘sexy’ dual speed 11:1 focuser. It resembles a phallus too and ‘looks the part’ alongside you in a comfy, twoseater sports car. But if you’re thinking Biblically, using your eyes and brain as God intended you to use them, then it’s easy to see that the 130mm gives a much brighter, cripser and more detailed image at the same magnification and all with perfect colour correction (the refractor only approximates true colour correction). In previous work, I showed that the 130 Heritage truss tube configuration could split tighter double stars, resolve finer planetary details and pulled in fainter deep sky objects than the aperture—challenged refractor. Using inductive reasoning (but also adding my own ongoing experiences to the mix), the closed tubed 130P ought to do likewise….. and it does.

Here’s the rub though. The optically inferior refractor is valued much higher than the reflector; many times more in fact. Why? God only knows! But I’ll give you my opinion;  because it is seen through the corrupt lens of the phallus. You’re literally thinking like a Dick. That’s the ridiculous situation that has precipitated because of our blinkered perception of value and which has gone largely unchecked for nearly three decades.  What’s the refractor really worth? To a visual observer, slightly less than the reflector, surely?

Don’t be a phallus.

Get real!

Date: November 10 2017

In case you’re wondering, the 130P is actually slightly lighter than the 90mm Apo and should probably cool off just as quick as the latter. It’s also small enough to fit in a comfy twoseater, so there’s absolutely no excuse not to consider it as a most powerful grab ‘n’ go telescope.

Looks can deceive: the 130P is lighter than the 90mm Apo.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

This very morning I set up Plotina in my back garden to exploit the feeble autumn sunshine, looking at the now denuded branches of deciduous trees located a couple of hundred yards distant. Incredibly, I was able to crank up the power to 406 diameters using a Vixen 1.6mm HR eyepiece and the images garnered were beautifully sharp and rich in detail. That’s over 80x per inch of aperture folks; no’ bad…..ken.

Yesterday evening the veteran Romanian observer, Mircea Pteancu, kindly reminded me that he has managed good splits of 52 Ori , 36 And, Antares and Nu Sco, using a homemade 127mm f/7 Newtonian reflector, adding another experienced voice to the list.  You can read more about his findings here. F/7 must be a wonderful place to be in a 5 inch reflector. I bet it would hardly ever need adjusting and focusing would be child’s play. I’m envious of f/7 but f/5 will do admirably.

Low Power Sweeping

After I had finished with the students and grabbed a bite to eat, I noticed that there was a few clear spells and no Moon between 8pm and 9pm local time, so off out I went with the 130P and decided to stick with just one eyepiece; my good old SkyWatcher 32mm Plossl. The markings on the barrel are long gone by now but there’s still no mistaking it! Truth be told, it is one of my fondest and most used oculars. Delivering a power of just 20x in a splendid 2.5 degree field, I enjoyed beautiful views of the Pleiades, now climbing higher into the eastern sky. From my dark country home, the hinterland to this much loved open cluster is coal black in the telescope, its individual stars, tiny incandecsent jewels shining through the darkness. The 32mm Plossl gives a very well corrected field, with stars even at the edge presenting as very acceptable. It’s comfortable eye relief makes it a good choice for those who wear eyeglasses.

From there I ventured high overhead to the Perseus Double Cluster and boy was that a sight for sore eyes! It’s singular beauty never fails to set my heart racing and it was splendidly framed in the wide, well corrected field. From there I inched the telescope  further eastward, centring the wonderful Alpha Persei Association in the 32mm oculus. Thereafter, I swung the ‘scope back westward into Cassiopeia and enjoyed staring at the fascinating ET cluster for a wee while. It actually looks best in the Newtonian, as the upside down image presents it the ‘right way up’, as it were.  Sweeping the instrument through this constellation is always a special treat, with myriad Milky Way stars dazzling the eye.

Spotting a hole in the clouds in eastern Pegasus and Andromeda I homed in on the great spiral galaxy M31 now very high up, its bright, lenticular core showing up very well together with its gradually fading spiral arms. The two satellite galaxies were also apparent with averted vision. Moving west into Cygnus, I enjoyed the radiant colours of 30 and 31 Cygni, which are much more compelling in this telescope than they appear in large (70mm) binoculars. Comely Albireo was also resolved at this low power.

Finally, I swung the telescope over to Auriga, and after a minute admiring the silent beauty of brilliant yellow—white Capella and its starry hinterland,  I swept through the belly of the constellation, seeking out the compact open clusters; M36, M37 and M38. Though I could have done with more magnifying power, I was pleasantly surprised how well they looked at 20x.

I’m deeply impressed with the performance of this economical telescope, being capable of every kind of astronomical application you might need it for. In fact, it has no significant weaknesses. It’s very lightweight, so even those who are frail can get fair use out of it. Indeed, though I am personally enjoying the prime of my life, I can easily lift the telescope on its mount a considerable distance with only one hand. It’s easy to store too and won’t take up much room. I keep mine under my bed lol! It’s an unbeatable bargain for those on low incomes as well as pensioners, and will delight its owners with years of productive use.

Date: November 13  2017

Mounting Considerations

The 130 is so lightweight that it can be used profitably on a number of economical mounts. I generally use the Vixen Porta II with this instrument. The wonderful thing about the Porta II is that the tension on both axes can be adjusted to perfectly match the mass distribution of the telescope. The supplied hex wrenches that sit under the mount head can be accessed at a moment’s notice to make those small but important adjustments to the tension that make the telescope move very smoothly, even at high power.

Plotina towards the zenith and beyond.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Because the telescope has a standard set of tube rings, one can also adjust the position of the instrument’s base so that observing at the zenith is easy to achieve.

The Porta II can also be adjusted in height to permit very comfortable, standing or seated observations. Thus far, I’ve only observed through the telescope in the standing position, as the weather has been so unsettled that a shower can turn up necessitating the instrument’s rapid transport indoors. But I hope to enjoy this telescope with a comfortable seat during more settled spells.

Tools an’ that.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The same telescope can also be neatly mounted on the simple table top mount supplied with the Heritage 130P. When mounted on a small table, it can be used with ease for low and medium power sweeps but I would recommend a more sturdy mount for the highest power applications.

On a table top.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

And for those who enjoy equatorial mounts, the instrument is well matched to the fairly lightweight EQ 2 mount. Indeed, one can purchase the 130P along with the EQ 2 mount as a package from SkyWatcher or Orion Telescopes & Binoculars(USA). These mounts can easily be upgraded for smooth motorised tracking too.  See here for a quick over view of its operation on such a mount.

There is also a number of lightweight, fully computerised GoTo mounts that can be mated to the 130P if that is your thing.

These are just some of the mounting configurations you can use with this telescope. None will break the bank and all should provide years of hassle free use. My preferred mounting for this fine instrument is the Vixen II as I’m not entirely bowled over by equatorials. It has given this author several years of flawless use with a number of telescopes, and has travelled with him the length and breadth of the country.

 

Daylight Use

Observing the last leaves of autumn in a bright blue sky!

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

During the middle months of the year, where sunlight is abundant and the length of the day is long, smaller aperture spotting scopes make near ideal tools for studying nature, but as winter approaches (and at dusk and dawn) at high northern latitudes, having decent ambient light becomes much more of an issue. This is where the significantly increased light gathering power of the 130P really shines. On a dull, overcast, winter day, only a couple of hours of decent lighting is available for nature studies. But it is in these conditions that the 130P shows itself much superior to conventional spotting ‘scopes. Where powers of 100x or above are really stretching the 80 or 90mm ‘scope, powers twice that and more are achievable with this ultraportable 5.1” Newtonian.

Of course, the Newtonian reflector provides an upside—down view of terrestrial scenes and while there are ways of getting decent right—side—up views, in practice it matters very little. When coupled to a digi—scoping device, the images can be easily inverted later on your pc.  When you’re examining the fine structure of tree trunks and branches or the splendid high magnification detail of leaves, rocks and wildlife in ultra—high resolution, you’ll soon forget about those upside—down images and delight instead on the rich details afforded by this optically excellent light bucket.

Because it gathers a very generous amount of light, you can also employ filters such as a polariser to cut through glare in the landscape and increase contrast on the brightest days.

A modern zoom eyepiece delights all the day long.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Indeed, using both the Heritage 130 and the closed tube 130P extensively during the day has caused this author to question the dominance of other kinds of telescopes in daylight applications. It might not look quite as sexy as a Questar 3.5 or 80mm shorttube refractor but one look through the Newtonian will quickly reveal its clear superiority to the latter. And of course, there will always be some who balk at the Newtonian and reject it only because of its inexpense; sad I know, but that’s their problem and not yours, right? lol!

Don’t be a slavish follower of fashion; take your daylight observing elsewhere.

Date: November 14 2017

The last several nights were either cloudy or too unsteady to continue some of the high resolution work mentioned previously. Many of the clearest nights have been cold but very turbulent owing to strong northerly air flows, which always deteriorate high magnification views in these parts. Things were so bad in the wee small hours of Monday morning last that the telescope was unable to steadily hold the four brightest members of the Orion Trapezium! But I am thrilled to bits with the deep sky performance of the 130P. The Great Nebula still looked magnificent in the opulent field presented by the 8mm setting of the Baader zoom eyepiece (81x) and far more compelling than either of my shorttube refractors (80 and 90mm) can ever deliver. It’s a powerhouse of honest to goodness performance!

I will report some more once conditions improve.

Date: November 16 2017

Plotina; rising above it all.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

I enjoyed another bright and sunny late morning/early afternoon session with the 130P. I re—tested its ultra—high power performance on daylight targets. I can again confirm that the instrument is good to go at 406 diameters i.e. the image remains fine and bright and beautifully crisp across the entire field of a Vixen 1.6mm HR ocular. For the most part though, I am sated under these conditions by the 183x vista rendered by my Baader zoom and dedicated shorty Barlow, which delivers an amazing 0.4 degree true field.

Iblis scurries to and fro, scheming, desperately seeking to inflict harm on her. Yet no matter how much mud the enemy flings at Plotina, nothing sticks.

Like a faithful Collie, she just goes on strutting her stuff, by day and by night; naturally, gracefully, effortlessly; delighting her master.

Tonight looks good for yet another session under the stars.

Time: 22:30 UT

Temperature: 4C

Seeing: 2.5 Ant, excellent sky transparency, brisk westerly winds driving in some intermittent wintry showers.

Tonight, I set up Plotina to assess the seeing and targeted Theta Aurigae now situated favourably well above the horizon in the east. The telescope delivered a wonderful split of its B and C components at 271x. The former is tucked up real close to the substantially brighter primary (magnitudes 2.6 & 7.2, respectively) with a separation of about 4″.

One of the keys to getting success out of a Newtonian telescope on such high resolution targets is to be patient. The telescope generates some thermals especially on colder nights, where the high magnification image breaks up momentarily before coming back together again. One moment it morphs into a swollen mess of light but as it moves across the field the image settles down and delivers beautiful, textbook perfect images. You need to spend time with the telescope to learn how it behaves before you can get the most out of it, or to speak, with gravity, concerning it.

But I had bigger fish to fry. High overhead at this latitude on mid—November evenings lies mighty Cassiopeia, and under these fine conditions I homed in on Psi Cassiopeiae, a system I have given mention to in regard to a very fine Orion 18cm f/15 Maksutov cassegrain I put through its paces a few years back. The primary shines with a beautiful soft orange hue but about 20″ off to the east of it lies the faint C and D components (magnitudes 9.2 and 10.0 respectively) and are separated by a mere 2.3.” The challenge is to be able to see them clearly. Needless to say, the large Maksutov made light work of these faint companions but my field notes show that I could also see them with my very fine 5 inch f/12 classical achromat but only with a concentrated effort. The test tonight was to establish whether or not I could do the same with this 5.1″ f/5 reflector and I can report that the answer is affirmative! I employed a magnification of 183x and a concentrated gaze. This is not an easy target, but it is just possible with this telescope under near ideal conditions.

What does this observation establish you may ask?

It shows that the light gathering power and resolution of the 130P is on par with the 127mm f/12 refractor.

No’ bad, ken.

I ran in to inform my wife of my progress but loitered too long beside the fire, unfortunately. When I went back outside, it was raining and the poor telescope (and some choice oculars to boot) got a substantial drenching!

Shockeroonie!

The wee HR got a showerin’ ken.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

But the 130P is no’ a Big Jessie ‘scope and a dousing of water from heaven does little to dampen its enthusiasm.

Bleedin’ showers ken…

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Date: November 17 2017

If it wasnae fur yer wellies, where would ye be? lol

Aye.

You’ll be glad to know that Plotina made a full recovery and is now ready for more action under a starry sky.

Weather still looks iffy though but since the telescope cools off as fast (maybe faster; greater surface area an’ that?) than a small refractor, it can still be used as the ultimate shower dodger.

Shower Dodger.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Date: November 18 2017

More on Faster, Cheaper, Better

It was another crisp, cool and bright day here in Scotland. And with some free time to cogitate upon the 130P, I can confidently report that its performance lies midway between a high quality 4 and 5 inch refractor, but at a much reduced price to the consumer. As I’ve demonstrated, it ticks all the boxes that an ‘apophile’ might make in an argument concerning image fidelity, portability, rapidity of cooling etc. How it looks should be of little concern to a dedicated observer, but maybe some value ‘form’ over ‘function;’ why, I’ll never understand!

Telescopes are not idols.

It must be stressed that my major objection to apochromatic refractors is their exorbitant cost per millimetre of aperture; a price I am personally unwilling to pay as I can make much better use of my disposable income (I’m frugal and I consider that a virtue). Simply put, their prices are far higher than virtually any other type of optics on the market and that alone will make them a prime target for new and more cost—effective technologies now being developed. Unless the prices of these instruments are significantly reduced, they will be superceded by new technologies that are faster, cheaper and better. For example, a few years back, this author introduced the amateur community to a novel flat lens technology that will surely revolutionise telescope optics if the good Lord grants us enough time to see it to fruition. The technology (now being developed for visual wavelengths as the article indicates) is scalable and affordable. Let us hope that they succeed in their researches!

In the meantime though, it pays to take a hard headed look at other affordable telescopes already on the market, and in the same aperture class as the 130P, to see how they measure up. As I said before, the 130P is in a completely different league to 80mm ED ‘scopes and 90mm Maks  (including the venerable Questar 3.5). Consider if you will, the Celestron C5, reviewed here in good detail. The instrument is quite portable but will take considerably longer to acclimate if taken from a warm room to the cold night air. With a focal length of 1250mm (so f/10), it offers up a maximum true field of about 1.25 degrees; that’s only half the field possible in the 130mm Newtonian! And with a central obstruction of 37.8 per cent, its performance on lunar and planetary targets will be noticeably inferior to this reflector (recall it’s only 28 per cent and mine was reduced to 27 per cent). Price wise, you can purchase a 130P and decent mount for much less than the C5 optical tube assembly alone!

Better still is the 127mm f/12 Maksutov. This has an even longer focal length (1500mm), reducing the maximum true field to about 1 angular degree. But it still has a central obstruction of 33 per cent and takes quite a while to acclimate (that is, if you’re unprepared!). 33 per cent is, of course, better, but not nearly as small as the obstruction in the 130P. This means that if the latter optics are decent, well collimated and suitably acclimated, it should outperform the former on low contrast targets under good seeing conditions. In this realistic review, the author correctly concludes that the 127 Mak rivals that of a top class 4 inch refractor in average conditions. So a good 130P (also cheaper than the 127mm Mak) such as the unit in my possession, should do that little bit better don’t you think?

Date: November 23 2017

At home with ultrahigh power.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

A Virtuous Telescope

After several days of rain and cloudy skies, the weather has turned much colder once again, bringing bright blue skies by day. Much of the north of the country got its first fall of snow in the wee small hours and we even got a sprinkling here but it didn’t settle. Making the most of the bright light, I once again tested the ultrahigh power performance of the 130P on a number of targets between 50 and 200 yards distant. Charging the telecope with a power of 406x, I got precisely the same results as I obtained before; namely, the telescope yields very sharp and detailed images (n=3) at this power, testifying to the quality of the optical system. This power ought to be useable on the best nights to ferret out the tightest doubles accessible to the instrument.

Today, of course, is American Thanksgiving Day, and I would like to wish all my USbased readers happy holidays!

Conditions look clear for tonight, so I may be able to report back later this evening. Tomorrow we travel 127 miles north for a short vacation. Needless to say, Plotina will be travelling with us in the hope that I can enjoy a short adventure with her under a very dark, winter sky.

I could do with a carry case for the telescope. But it’s certainly not an essential feature. Afterall, the instrument can be carried in your lap, or safely stored with the rest of the luggage in the boot of the car. And even if it gets knocked about, it’s easily remedied by a quick and accurate collimation once we arrive. No sweat!

I’ve just noticed that the eyepiece holder can accommodate a T2 adaptor to mate a camera or webcam to the telescope. That’s a nice touch, but something that doesn’t interest me, as I’m purely a visual observer, but it does means that the instrument can be used to do some entrylevel imaging when coupled to a motorised tracking mount.

Gosh;  are the virtues of this telescope ever going to come to an end? I wonder!

Time: 17:00 to 17:30 UT

Temperature: 0C

Seeing: IIIII, very cold, a little turbulence, crescent Moon setting in the southwest, no cloud.

This evening I obtained a beautiful split of Mu Cygni at 271x but a decidely better one at 325x. Secondary situated northwest of primary and much better resolved than in the smaller refractors (ST80 & ED90).

Lambda Cygni attempted also; very strong elongation but not resolved at 406x.

Some cloud moved in after 5.30pm local time raising the temperature by a couple of degrees in the process. Hoping for more observations later tonight.

Date: 24 November 2017

Time: 00:50UT

Seeing: IIIII, remaining a little turbulent, cloud clearing away after 23:00 UT

Temperature: 0.5C

A few high resolution targets selected this evening

Eta Orionis: a very nice split at 271x, pure white components; images improving as the system approached the meridian afer midnight. Twenty minutes can make all the difference on this mediocre night.

Theta Aurigae: Now very high up and beautifully presented in the 130mm speculum at 271x.

Rigel: Not really a high resolution test so much as an indication of how much light scatters at lower altitudes; quite low down when observed but faint companion easily picked off in the high fidelity field of my very good Parks Gold 7.5mm ocular delivering 87x.

52 Orionis: A good result! Stars appeared elongated at 271x and 325x but not resolved. Will have to wait for another good night to crack this 1.0″ pair. But my observations give me confidence that it will yield in good time.

 

Time: 11:30 am

Inbox filled with Black Friday junk; the unpleasant side of global consumerism.

All deleted now!

Thanks but no thanks!

Date: November 27 2017

Well, our weekend away went swell. Even though we left with about an inch of snow on the ground, the main roads had scarcely any of the white stuff. Indeed, it was only to be  found in the high places along the route. Arriving at our destination at dusk on Friday, the sky remained resolutely clear, but a bitter north westerly wind made it feel a lot colder than it was (fluctuating by just a couple of degrees above and below freezing). After we had settled in, I took the little reflector out of the boot of the car and secured it on its Porta II mount. Checking how well the instrument maintained collimation, the laser showed only slight misalignment of the secondary mirror. Indeed it was pefectly useable as it was for low and medium power work up to 120x. To be honest, I wasn’t really surprised. You see, the acquisition of her winter coat has made the telescope much more robust. Nevertheless, I made that slight tweak to the secondary to bring it into perfect alignment. No sweat; it only takes a few seconds.

A beautiful, late crescent Moon greeted us in the south southeast, the magnificent orb culminating at about 5:30pm, just above the tree line of the grove that marked the edge of the property. In a race against time, I fetched my trusty Baader zoom and dialled in the magnification that would provide the most majestic view; the 8mm setting yielding a power of 81 diameters, which would frame the entire crescent with plenty of dark sky to spare. Though the air was a tad roily, the image was still breathtaking!

Plotina in winter apparel (Rural Abedeenshire, Northeast Scotland, November  25 2017).

Because we had company, that was all the observing I got up to, apart from a wonderful half hour in the bright, early afternoon sunshine of Saturday (406x testing very favourably at this location too, so n = 4). Yet even these brief spells of observation were more than enough to reaffirm the worthiness of this instrumrnt as a choice travel ‘scope. Indeed, it has already been with me on several other trips the length and breadth of the country, where I discovered that skies can be great away from home.

Plotina in summer apparel on Skye, Northwest Scotland (August 2016).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Plotina watching leaves at 243x  in Wigtown ( July 2017), southwest Scotland.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

There it is!

Travelling: yet another virtue of the telescope.

Intelligent Design

While carrying out my observations I became increasingly aware of the tendency of the simple 6 x 30mm finder to slip out of position. Even with an elastic band in place under the collar of the finder bracket, it still slipped more than I liked, necessitating a small readjustment in the field. This is a minor nuisance, and one I could easily live with, but I also discovered that the bigger, 9 x 50mm finder that normally sees light astride my main telescope; a 20.4cm f/6 Newtonian, also fits the 130P perfectly!

A good telescope with an aperture of 5.1 inches really ought to have an equally good finder. Unlike the 6 x 30mm, the 9 x 50mm is much less inclined to go out of alignment while in use and ought to pull in even fainter objects, increasing the 130P’s overall efficiency. The small additional mass up front is easily handled by the Porta II mount.

Serious fun! Plotina with her upgraded finder.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

I think that’s a good thing. Afterall, the equipment I have already invested in ought to be able to serve me in diverse ways and when I want to go for a serious night out with Plotina, I’ll be needing a serious finder to complement her excellent optics. In fact, I’m thinking of doing something similar with Gaius, my 80mm f/5 achromatic. It would be just dandy to use it on either my 8 or 12 inch telescopes!

Pint sized powerhouse.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

This afternoon, I took the 130P out for another look at the landscape. Focusing on a conifer tree some 150 yards distant, I once again obtained a tack sharp image at 406x (n=5). The instrument is probably capable of doing 100x per inch though (used to study tiny planetary nebulae and very tight doubles under good seeing conditions). I consider that exceptional!

The Lap ‘Scope

Can Plotina be used without a mount?

Back in 2010, amateur astronomer, Douglas Bullis, wrote an interesting Cloudy Nights article describing his “lap ‘scope,” a bare bones 6″ f/5 Meade Schmidt Newtonian(SN6). In the article, Bullis made the bold claim that the modified instrument was not a grab ‘n’ go ‘scope so much as a grab ‘n’ sit instrument. Be sure to check out the comments as well!  Having owned and used a SN6 for a couple of years, this author is confident that the 130P would make an equally good if not better lap ‘scope, allowing one to make 20x sweeps, delivering a 2.5 degree field.

The lap ‘scope.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Of course, Bullis’ article is nothing new. In the 2001 book, Astronomy with Small Telescopes, the then Sky & Telescope columnist, Jay Reynolds Freeman, described his own lap ‘scope, a 6″ f/5 Newtonian reflector, showing that the concept has been alive and well for quite some time now.

Can you think of a more versatile instrument than the 130P?

Date: November 28 2017

Time: 01:25 UT

Seeing: very good, II, excellent transparency, no clouds.

Temperature: 3C

A most successful evening!

I began shortly after midnight seeking a split of Eta Orionis. This system was easily resolved at 271x.

Next, I turned the telescope to 32 Orionis, easily found near Bellatrix; an interesting and very tight pair at 1.3″ but the magnitude differential is about 1.6 (4.2/5.8). Charging the telescope with additional power ( x406), I ran the system from the edge of the eastern field and left it drift through until it reached the western field stop, and repeated this procedure several times. To my delight, it was a fairly easy split!

Next I moved over to 52 Orionis (a tighter, 1″ pair), near the bright winter luminary, Betelgeuse. Though I was monitoring this system for about half an hour, I found it considerably more challenging than 32 Ori. But at 01:15 UT as the system crossed the meridian, a power of 406x was just enough to prize these two nearly equal magnitude stars apart!

Would like to have used a bit higher power with 52 Ori.

Both systems orientated roughly NE to SW.

A glorious sky here!

Will discuss more later today.

Time: 11:00 UT

Last night’s work with the 130P was very encouraging. It shows that this small Newtonian reflector is an excellent double star telescope and capable of resolving pairs down to its theoretical limit.

I encountered a little issue while using the larger 50mm finder. At low and medium power, the larger finder worked well but while using the ultra high powers to tease these stellar pairs apart, I found it to introduce greater vibrations while focusing and that’s not a good thing. I thus switched back to the lighter 6 x 30mm while conducting this work. I  just need to place some cardboard or some such under the collar to tighten it up. We live and learn; no sweat.

I am very much enjoying using this excellent grab ‘n’ go telescope. It’s just one sweet little instrument. I feel it gives exceptional value for money and has already paid its way many times over with the wonderful images it has delivered, whether in the open or closed tube configuration.

I see the One Sky Newtonian thread is still going strong on Cloudy Nights, with over 260,000 hits. Very well deserved in my opinion!

The addition of Bob’s knobs to the primary and secondary mirrors of this telescope has been highly satisfactory. I have just ordered another set of these to replace the ones I borrowed from my 8 inch Newtonian. They should be here tomorrow.

 

The cold snap continues; so I hope to make more observations with the 130P.

Time: 23:50UT

Concerning Fidelity

A strong northerly air flow has caused the seeing to degrade noticeably from last night ( IIIIV), especially with targets located at lower altitudes. That said, some good targets higher up were still well resolved including, Theta Aurigae and Iota Cassiopeiae (271x). The reader will note that these systems are often touted as being ‘tricky’. A consultation of the literature typically (though not always) states that they are “often difficult…. requiring steady nights and high magnification“. This is yet another urban myth. They are accessible much more often than is commonly reported in the popular literature. Why should that bother me? Well, it’s partly about honesty and partly about authority. If I’m buying a book on visual observing, I would expect the author to relay accurate information, and not perpetuate an untruth/exaggeration. Experience is the only panacea.

Concerning Outreach

The telescope is a wonderful outreach instrument. I like to set her up in the evenings when I’m busy with my students. Tonight, a few of them beheld the beauty of a waxing gibbous Moon, either when they arrived or before they left for home. The Baader zoom worked its magic on this target after dark, with lots of “oohs and aaahs,” coming from them as they settled into the telescope for a gander. Because it’s a robust, nofrills instrument, with decent aperture, the 130P makes an awesome outreach telescope. Easy to set up and pack away, you’ll never have to worry about things that go bump in the night. I can’t say the same for other types of ‘scope designs though. ’tis the genius of Newtonianism you see!

Date: November 29 2017

Rejecting Materialism

Happiness with Newtonians; Plotina (laevo) et Octavius.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

I thank the Lord that I live in a place where the laws of physics are actually obeyed. Can you imagine that! A good telescope with a larger aperture, given fair to good conditions, always proves superior to a significantly smaller one, even if the latter is that little bit better millimetre for millimetre. That said, I find it highly curious that there are some places where the basic laws of optics seem to be violated; such as in the refractor forum of Cloudy Nights. As a scientist trained to think critically, I am given to wonder where the real discrepancy lies; the observer or the environment?

When you’re not thinking like a phallus, you see things objectively, as things really are, not how you want them to be. And the results obtained with Octavius were perfectly in keeping with those garnered by Plotina when assessed against the 90mm apochromat in particular.

The old adage comes to mind; a fool and his money are soon parted.

The new knobs arrived late this evening and were promptly fitted to Octavius’ primary cell. Now all my reflectors are ready to work as they were designed to; right the way through the winter. Yeehaw!

Pharmakeia

Our Creator designed our bodies to work best while being sober, in our right mind, as it were. And no matter how much we wish to escape reality, no altered plane of perception  can improve on this blessed state. I consider it a big no no to observe while under the influence of alcohol or other pharmacological agents. Just one drink alters my state of perception and I have always maintained strict sobriety while observing or making reports from the field. That said, I wonder how many amateur astronomers observe under the influence of alcohol or some other mind altering agent. I believe about one in every seven Americans has problems with alcohol and the incidence is probably higher in many other nations. I know for a fact that some prominent CNers are on record for saying that they enjoy one or two scotches before venturing out of doors with their telescope(s). But if  objectivity is to be the goal of the observer, and if the truth is to be valued above all other things, such behaviour most not be condoned. It’s all well and good to enjoy a drink; but not while making observations with the intention to report them. This could contribute to a variety of anomalous results reported by some individuals over the years.

For me, telescopes are instruments to be enjoyed in blessed sobriety, the way our Creator intended it to be.

An Enabling Telescope

Date: November 30 2017

St. Andrew’s Day.

I don’t know about you, but I feel like I’m removing the cobwebs, pulling away the curtains, sweeping up the dust and opening the windows to let the light in. It’s as good a time as any to do so, and I hope that it will have a lasting effect on the hobby. I also hope that it will encourage more individuals to enjoy this wonderful passtime without fear of intimidation from the pretentious prattle of the gearheads.

Another beautiful but cold day here. With the Moon now growing rapidly in brightness, I would like to visit some of the easy, showpiece colour contrast binaries with the 130P this evening.

Could the 130P be your only telescope?  I think the answer is definitely *yes*. As I’ve demonstrated, it’s no one trick pony. Indeed, it does virtually everything you’d want to do with a telescope, and with an impressively high level of competence. Indeed, you could have an absolute ball with this instrument for many years.  But I am blessed with a few other telescopes that are more powerful (fine 8″f/6 & 12″ f/5 Newtonians); nothing overly flashy, but great workhorses nonetheless.

My transition to Newtonianism has been a worthwhile experience and, truth be told, the last few years of my observing career have been amongst the most productive and happy in my career as a telescopist. It’s been thrilling to see what they can do, especially in regard to high resolution astronomy. It feels right too.

Traditionally, one of the socalled advantages of refractors (and Maks too) pertains to their lack of maintenance. Reflectors, they claim, need some TLC to keep them in tip top condition. Although this is true, I question whether the lack of maintenance is being overplayed and whether it really is an ‘advantage’. For one thing, as I’ve said before, if you do have an accident with a refractor, then you’ll likely have to send it off to someone for professional realignment; which is not an especially pleasant prospect. More importantly though, are we to encourage slothfulness? Is it not good and fitting that the telescopist remain active; both mentally and physically? I dare say, the little bit of TLC needed to keep Newtonian reflectors in good shape is a blessing and not a curse. Personally, I’d rather remain a tinkerer than become bone idle.

Think Newtonians can’t work in the cold?

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Time: 17:30 to 18:00 UT

Temperature: -2C

Seeing: III, remaining a little unsteady, partially cloud covered, bright gibbous Moon rising in the east.

I had a spare half hour this evening so off I sped to some wonderful colour contrast doubles of the winter sky;

Albireo; now in the far west, always a beautiful sight in the telescope. Golden and blue stars wonderfully framed in the generous field offered up by the Baader zoom at 81x

Gamma Delphini: Now sinking into the southwestern sky. A beauty at 81x, with yellow and greenish components.

O1 Cygni; easily located between Delta Cygni and Deneb, this is a lovely sight in any small telescope and sure enough it presented beautifully in the 130P at 20x (Skywatcher 32mm Plossl) but even better at 81x. O1 is a K class star with a marmalade orange hue and just 4′ away lies 30 Cygni, which presents with a greenish tinge to my eye. And to top it all off, the 7th magnitude star SAO 49338 makes for a fetching addition to the field, located as it is just a few arc minutes east of O1 Cygni.

Gamma Andromedae (Almach): a corker at 81x; orange and green riding high in the eastern sky at this time.

Finally, swinging the telescope low into the far western sky, I picked up Rasalgethi in Hercules with its comely red and green components, easily split at 81x.

As I have demonstrated many times over the last few years, Newtonians work very well in sub zero temperatures. Therein lies yet another myth promulgated by those who wish to push refractors on other amateurs; another porky. Indeed I have split some of my tightest pairs with Newtonians in very cold temperatures. What is more, there is no correlation whatsoever between ambient temperature and seeing conditions. One memorable night a few winters back, I obtained a stunning image of the companion to Propus (Eta Geminorum), that ‘little blue pimple’, with Octavius, my 8 inch Newtonian, in freezing temperatures. And truth be told, I have not seen it so well since!

Please don’t cultivate untruths. It’s unfair and discourages amateurs from going out under the starry heaven during cold spells with their reflecting telescopes (and that includes large catadioptrics which were extensively tested by this author a few years back). It pays to remember the work of the Reverend T.W Webb and William F. Denning, who dared to venture out with their large reflectors (with no fans either) during cold winter nights to bring the beauty of the sky into your warm and comfortable living rooms.

Conclusions

The Newtonian reflector reigns supreme over all other telescope designs. And this 130P has earned a distinguished place in my collection. It will remain my grab ‘n’ go telescope of choice in the future. It’s modest cost will allow many more beginning amateurs to cut their teeth in this wonderful hobby, with its excellent optics and great portability, but it’s powerful enough to engage seasoned observers as well. Whatever your preferred targets for observation are; Moon, planets, double stars, widefield and high magnification deep sky, the 130P will not disappoint. It also makes a wonderful daytime telescope for nature studies.  I commend SkyWatcher for bringing this amazing instrument to market and wish them every success in the future.

Thank you for reading.

 

De Fideli.

 

New Adventures with the Shorttube 80 Achromat.

Gallus Beastie…… ken

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Dedicated to Dave Russell

Introduction

As you may know, I’ve written quite a bit (perhaps more than any other telescopist) about the venerable Shorttube 80 achromat. It’s a well–travelled ‘peashooter’ ‘scope that has punched well above its diminutive aperture and with thorough testing in the field, has exceeded all of my expectations. My particular model was purchased for about £150 and that extra cash bought me an instrument with a fully rotatable focuser that can accommodate 2 inch and 1.25 inch oculars, a well baffled internal tube and a retractable dew shield. The original crown & flint elements (branded as Opticstar) were replaced with a SkyWatcher objective and were professionally spaced and centred for optimal performance.

Gaius: my trusty 80mm f/5 achromatic refractor fitted with a Celestron 1.25″ prism diagonal.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

My 80mm F/5 achromat continues to serve as a highly capable birding ‘scope for crisp daylight images rich in contrast using my equally versatile Mark III 8–24mm Baader zoom, which delivers a very useful range of magnifications from 17x to 50x and with a generous field of view. Indeed, I consider this telescope to be far more versatile than a variety of 90mm Maksutovs that have come and gone over the years. The 8mm setting of the Baader zoom delivers a near ideal 1.5mm exit pupil which is especially good for enjoying larger deep sky objects (DSOs) in a generous 1.4 degree true field. Extensive field experience with this particular instrument has demonstrated that it can be used profitably at double this power to get close up views of smaller DSOs like small planetary nebulae and open clusters. For the widest ultra–rich sweeps, I adopt a simple but good 32mm multi–coated SkyWatcher Plossl eyepiece delivering a power of 13x in a near 4 degree field.

Because it’s a fast achromat, many observers have dismissed it as a high–resolution telescope incapable of delivering adequate high magnification views of the Moon, planets and double stars and this author would be the first to concede that it needs a bit of help when extending magnifications over 100 diameters.  That said, because I have grown very fond of this modest little ultra–portable telescope, I have sought long and hard to try to improve its optical performance at higher powers to make the instrument as versatile as possible. And that will be the subject matter of this blog.

As I have related before, I was rather taken aback by the ability of this telescope to resolve double stars within the remit of its aperture. Indeed, many hours of field work has allowed me to resolve an impressive suite of binary and multiple star systems very much at odds with received opinion. But like everything else in life, you’ll never know unless you try. Systems like Delta Cygni, Epsilon Bootis, Iota Cassiopeiae, Xi Ursae Majoris etc have all been resolved with this telescope under good seeing conditions and with nothing in the way of additional help. In recent months, I have been evaluating the performance of a 90mm f /5.5 ED apochromat in regard to the resolution of double stars and found that, like the venerable 80mm f/5 achromat, that this very fast telescope was equally capable of resolving such systems (indeed a little better owing to its greater aperture). The former instrument is fitted with a very fine 11:1 dual speed micro–focuser which has greatly aided precise focusing at high magnifications (up to about 250x) in the field. The shorttube 80, in contrast, is far more difficult to focus under the same high magnification regime owing to its single speed Crayford–style focuser, faster relative aperture (f/5) but also because at ultra–high powers the chromatic error of the telescope makes precise focussing far more challenging. And it was this issue that I decided to re–investigate.

The 90mm f/5.5 ED doublet used in comparison tests.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Unfinished Business

My experiences with the 90mm f/5.5 ED refractor as well as a 130mm f/5 Newtonian reflector showed that I could push these fast telescopes to powers as high as 250x and above profitably to tease apart tricky binary stars such as Mu Cygni A & B under good atmospheric conditions. I very much wanted to be able to do the same with the 80mm f/5 shorttube. Because of the latters’ smaller aperture, 250x would be about the upper limit that I could expect. My aim was to obtain the sharpest possible stellar images freed from (as much as possible) the chromatic ‘fog’ that attends pushing such a fast achromat to such high powers. Without changing the prescription of the lens (using an ED element), or stopping down the aperture (which I was unwilling to do), the only possible way was to remove the offending wavelengths from the image by blocking the principal offending wavelengths. And that led me, once again, to explore the use of filters.

The usual minus violet filters, which include the fringe killer, semiapo filter and Wratten no. 8 light yellow filter were a step in the right direction but not really good enough to do the job, as all of these do not remove all of the offending unfocused blue–violet wavelengths. What I sought was a filter that would remove all of the unfocused light but still allow as much light as possible to be transmitted to the eye. High efficiency light transmission would be a very important parameter, as at very high powers the images become especially dim in such a small telescope. My search was narrowed down to two such filters; an inexpensive light green Wratten no 56 and the (somewhat more expensive) Baader 495 longpass filter. The latter was brought to my attemtion by Dave Russell, an amateur astronomer based in Upstate New York, who carried out extensive tests using his 140mm f/5.7 Vixen Neoachromat. Below are the published transmission curves for these filters.

The light transmission curves for the Wratten light green filter.

 

 

 

 

 

 

 

 

 

Light transmission curve for the Baader 495 long pass filter.

 

 

 

 

 

 

 

 

 

 

Daylight Testing

I conducted a series of tests during cool, bright autumnal afternoons, where the temperatures did not fluctuate up or down. My targets included. for the most part, leaves from the topmost boughs of trees located between 80 and 150 yards away. The 1.25″ diagonal on the shorttube achromat was threaded with either the Wratten no. 56 or the Baader 495 longpass filter. The 80mm f/5 was charged with a power of 250x using a 1.6mm Vixen HR eyepiece, and as a control, I stopped down the 90mm ED ‘scope to 80mm using a makeshift cardboard aperture mask and used a 2mm Vixen HR ocular to derive the same magnification (250x).

The Vixen HR 1.6mm eyepiece used with the 80mm f/5 achromatic telescope.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The results for both filters were remarkable! The light green filter did very well indeed, removing the vast majority of the offending short wavelengths, but the 495 long pass filter removed all of it. The images derived were very sharp and punchy using both filters, as if a foggy veil had been lifted from both images that greatly increased the contrast and sharpness at these uber high magnifications. This type of transformation was not noted with the aforementioned minus violet filters which only remove about half of the offending secondary spectrum. Both images were really quite excellent and almost as sharp as that derived by the ED ‘scope on the same target using the same magnification. The only significant differences were the colour casts generated by the filtered achromatic images; the Wratten gave a green cast, the Baader longpass, a yellow hue.  In addition, I carefully noted the brightness of the images. This time there was a clear winner; the Baader 495 longpass filter, which was clearly transmitting more light to the eye.

Consulting the data on the Wratten no. 56 filter revealed that its light transmission is about 53 per cent. But as you can clearly see in the hand–held images of both filters below, the Baader 495 longpass transmits significantly more light.

Light transmission comparisons between the Baader 495 longpass filter (left) and the Wratten no. 56 filter (right).

 

 

 

 

 

 

 

 

 

 

 

 

These daytime tests showed that the 80mm f/5 achromat could indeed generate very sharply focused images when the blue–violet secondary spectrum was completely removed. It also showed that the Baader 495 longpass filter was generating a significantly brighter image at 250x since its passes practically all visible wavelengths beyond about 495nm. In contrast, the Wratten absorbed most of the offending blue–violet and a significant fraction of red wavelengths (as indicated by the transmission curves shown above).

The author is aware that the Vixen HR series of oculars are very expensive and may be beyond the budget of some amateurs. Thankfully, there are other ways of deriving the same high magnifications using less expensive eyepieces. For example, I could achieve a power of 240x with the shorttube 80 by mating two shorty Barlow lenses to a 6mm orthoscopic eyepiece with broadly similar results.

Very high powers can also be achieved by stacking shorty Barlows to more economical eyepieces. In this case, a 6mm orthoscopic was mated with a 2.25x Baader Barlow as well as a 1.6x Barlow made by UK Astroengineering. Note that the configuration doesn’t protude too much above the diagonal.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Under the Night Sky

Keeping the longpass filter in the diagonal and turning the telescope to the bright stars Vega and Deneb, the filter imparted a beautiful golden tint to them which I didn’t find distracting.  In most fields where the brightest stars were absent, one would be hardpressed to notice that any filter was in place. Turning next to the Pleiades and Perseus Double Cluster, the filtered images appeared every bit as bright as the unfiltered view with little or no light loss that I could discern; and which came as quite a relief to me. The lattter clusters, in particular, appeared very striking in the generous field of view served up by the Baader zoom at 50x. Red stars were especially easy to see and indeed were slightly enhanced using the filter. More generally, stellar images appeared tinier and more intense with the filter in place. The Andromeda Galaxy, now very high in the sky, stood out beautifully against a sable hinterland at 13x. Then I swung the telescope over to Lyra, now sinking into the western sky and located the Ring Nebula. Comparing the filtered and unfiltered views at 100x, I was very pleased to see that the images were quite comparable with only slight dimming in the latter. This showed that the filter was passing most if not all of the doubly ionised oxygen (500.7nm) which sets these planetary nebulae aglow. This will come as good news for those amateurs who like using larger aperture short focus achromats in pursuit of emission nebulae.

Gaius enjoying a clear autumnal sky.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

At higher powers, the stellar images snapped to a very tight focus with zero chromatic fogging much more easily than in the unfiltered view. This is a real bonus as there was now far less ambiguity to the position of best focus than when attempting to focus without the filter. Some may dislike the colour shift in the stellar Airy disks but, truth be told, this was of little concern to me as all I wished to do is to get very tight and tidy stellar images at the highest powers. Indeed, the ED ‘scope (a very good FPL 51 doublet) also imparted a slight yellowing to the Airy disks at high powers (above 150x) which departed somewhat from their true colour. Were I looking to get accurate colour information though, I would unhesitatingly recommend neither instrument over a 130mm f/5 Newtonian reflector which will always reveal the true colour of the subject stars as well as being able to resolve tighter pairs than either of these refractors (and retails for about 1/7th of the price of the ED telescope to boot). In short, the goal was never to turn the achromat into an apochromat but only to allow me to achieve the brightest and tightest Airy disks at the highest powers.

High Power Night Time Tests

Shortly after 7pm local time on the evening of October 27 2017, I set the telescope on its Vixen Porta II mount and directed it at a first quarter Moon that was now culminating low in the south. A brisk westerly wind was blowing, carrying cloud patches over the landscape but there was enough clear spells for me to assess the image using the longpass filter. I charged the instrument with my Baader zoom and dedicated 2.25x Barlow and dialled in the 8mm setting yielding 113x. This particular configuration provides a wonderful panoramic view of our companion in space, its generous field allowing the entire lunar hemisphere to be examined at once.

Even without the filter, the image was quite good but it was plain to see that the crater rims were tinged in unfocused blue–violet and as Dave Russell previously reported with his 140mm Neoachromat, the entire surface was bathed with a faint ‘lavender fog’  which softens the image ever so slightly and which cannot be focused out. With the filter in place, the Moon took on a striking yellow–green countenance but the sharpness of the image was noticeably improved. Gone was any trace of unfocused light and the lavender fog completely removed. The prominent northern craters, Aristotle and Eudoxus were beautifully sharp, and the many ridges within Mare Tranquilitatis really stood out. The image just snapped to focus (and at f/5 you’re either there or you’re not!). Moving further south, the craters Hipparcus and Albategnius were stunningly presented with perfect delineation between their sunlit and shaded floors. And then my eye met with the rugged southern highlands presenting Theophilus, Cyrillus and Catharina  perfectly as if etched out with a laser. To be honest, I found it hard to take my eye away from this visual banquet but I eventually switched to higher power, inserting the 2mm HR ocular delivering 200x. Again, the image snapped to a sharp focus and yielded wonderful details. The lunar Apennines were simply astounding to study at this high power with excelllent contrast and no image breakdown whatsoever! Mount Hadley stood out boldly near the location of the Apollo 15 landing site.

My findings agree very well with the reports made by Russell. This is one excellent filter for lunar studies, transforming an otherwise mediocre 80mm lunar ‘scope into a very good performer. Because of its small aperture, a telescope such as this is relatively insensitive to the vagaries of the Earth’s atmosphere and I went away from the field fully confident that I could push the instrument to still higher magnifications on this wonderful target under better observing conditions.

Impressed? Chalk it down!

On the evening of October 28 2017 at 7:30pm local time, I set up both the 80mm f/5 achromat (with the 495 longpass in place) and the 90mm ED refractor stopped down to 80mm to get another look at the Moon in the south. Conditions were blustery all day but a clear spell came between 7pm and 8pm. Hoping for the best, I quickly discovered that the seeing was horrendous lol (Antoniadi  IV). What a difference a day maketh! Views were just passable at 113x in the 80mm f/5 and lousy at 200x. But precisely the same was true with the ED ‘scope. At powers of the order of 100x the images were just useable, but at double that magnification, it was well nigh impossible to get a sharp focus.

This was also confirmed on a double star situated much higher up in the western sky. Turning to Epsilon Lyrae 1 & 2, neither telescope could convincingly split the stars at a power of 200x. These observations provide an important lesson in their own right. Even small telescopes are not immune to seeing. And though the ED refractor is of unquestionably higher optical quality than the shorttube 80, the seeing conditions on this occasion completely overwhelmed both instruments.

The Meat

On two evenings of good to excellent seeing (October 25 and 29, 2017) I was finally able to test the high resolution performance of the longpass filter with the 80mm f/5 achromatic telescope, using the aforementioned stopped down ED ‘scope as a control. Examining the images of Epsilon 1 & 2 Lyrae at 250x, the filter enabled me to achieve precise focus easily and consistently. The Airy disks appeared clean, greenish yellow in hue and round as buttons! Light transmission was excellent. The same was true when I tested the telescope on Delta Cygni; the companion being readily seen in the very good seeing conditions presented on these two evenings. But the proof of the pudding, as it were, lay with Mu Cygni A and B (very near the Dawes limit for such an aperture), which I have found to be exceedingly difficult to image well using the native 80mm f/5 achromatic optics, with the best views delivering a vaguely dumbbell like morphology. For reference, the 130mm f/5 Newtonian makes light work of this system and the pair is just resolved at 250x using the full aperture of the 90mm f/5.5 ED refractor. But stopped down to 80mm in the latter ‘scope, the pair was consistently seen to be touching. Using the longpass yellow filter on the ST80 finally allowed me to see these stars distinctly at 250x, the two Airy disks indeed touching each other, like a tiny snowman in the sky, the fainter companion (4.8/6.2) orientated roughly northwest of the primary; and just as the stopped down ED ‘scope had delivered. This is good evidence that the 80mm f/5 telescope can resolve to its theoretical limit, presenting images that are accurate representations of reality.

I am confident that the filter can indeed improve the performance of the telescope at the highest powers. It further dispels the myth that the ST 80 cannot do this kind of work. As usual, I attribute this to an admixture of laziness, the presumption of inadequacy, and sheer lack of interest.  As ever, I would warmly encourage others to follow my work and to confirm these or related findings in due course.

The reader will remember that such a telescope has no need of such a filter (or any other filter) for low and medium power work (up to 100x or so). Indeed, this author is of the firm conviction that the very acceptable levels of secondary spectrum produced at these modest powers are desirable, educational and comely, in equal measure.

The longpass filter will also be utilised as a tool to enable me to obtain the sharpest possible images of the brighter planets when they come around. And while, in this capacity, I have obtained very encouraging results last season using the No. 56 Wratten filter, the longpass should help it perform that little bit better.

What other telescopes might benefit from using the yellow longpass filter?  Certainly, a variety of fast achromats come to mind but I would caution that as the aperture gets larger and the focal ratio is kept low, sphero–chromatism will quickly overwhelm the ability of such a filter to perform as it has done in this 80mm ‘scope. The reader will recall Russell’s comments that the secondary spectrum on the ST80 is not overwhelming to begin with (indeed it is similar to that seen in a 6 inch f/8 instrument) and so the filter need only be used where the highest resolution is sought (planets and double stars). The author is also aware that Russell’s instrument is a Petzval design, so has a longer focal length doublet to start with. Still, I would encourage others to experiment using the more recently introduced 6 inch f/5.9 achromats, as well as the ubiquitous 100mm, 120mm, and 150mm f/5 achromats on the market.

That’s where this blog winds up. So ends the tale of my quirky little achromatic.

Thanks for reading!

 

Postscriptum: For more on what can be done with the Shorttube 80 achromat in regard to splitting close binary systems see pages 39 and 43 of the the book, Astronomy with Small Telescopes (2001), where a number of suitable targets and magnification regimes are discussed. Happy hunting!

Gaius.

Neil English’s soon to be published work; Chronicling the Golden Age of Astronomy, calls upon the vast resources of history to debunk many other telescopic myths.

 

De Fideli.

The ‘Foot’ ‘Scope Project

Fintry, July 2017.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


Saturday July 8 2017

I took a chance on a large reflecting telescope; a Dobsonian with a 305mm (12”) mirror and focal length of 1525mm (so f/5 relative aperture). The price was just too good to pass on so I contacted the seller and it transpired that he was a professor of optics from a Welsh University. I asked him about the telescope and in particular, about its optics. He assured me that they were good from his limited use of it, a tad over corrected but otherwise fine. When I enquired as to why he was selling the telescope he simply admitted that he didn’t have much time to use it and would rather see it collecting starlight than sitting in his garden shed. Although based near Chester, England, the owner kindly agreed to drop off the instrument in person (with an appropriate reimbursement for pertrol) and so early on Saturday morning, he and his wife set out on the road north to my home here in rural central Scotland. The day was bright and sunny, good for a car trip and they arrived in the mid afternoon.

Branded as a ‘Revelation’ 12” f/5, the instrument is fitted with GSO mirrors, which, as I have shown in previous blogs, has now established itself as a manufacturer of high quality optics at very reasonable prices. A few years back, I had actually tested one of these units but, unfortunately, found the mirror to be astigmatic; a real show stopper for me as I like to push my instruments on high resolution targets.

Larger than life: the Revelation 12″ f/5 Dobsonian dwarfs Plotina, my ultraportable 5.1 inch f/5 reflector (shown on the left).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The instrument came with all the usual accessories; a 9mm Plossl (1.25” fitting), a 30mm wideangle ocular (2” format), an extension tube and a ‘straight through’ 8 x 50mm achromatic finder ‘scope. And while the original instrument came with a built in fan, the owner apologised that he had taken it off whilst installing a set of stronger springs to support the primary mirror and had forgotten to reinstall it. He was relieved to see that I wasn’t in the least bit bothered about it and reminded him that many of the great observers of yesteryear never used fans on their reflectors and that this didn’t seem to hinder their fine work in any significant way. He gave me a wide smile. I handed over the cash and treated the couple to high tea, where we discussed, among other things, the many virtues of the Newtonian telescope. Suitably refreshed, my wife and I bid them farewell and they began their long car journey south of the border.

No sooner as they hit the road, I visually inspected the primary mirror and found that it had accumulated quite a bit of dust, which imparted a milky appearance to its surface. There was no evidence of coating deterioration on the primary mirror, but it would require a good cleaning, so I removed it from the tube, gave it a ‘finger tip’ cleaning, described previously in this short blog, using a few drops of washing up liquid added to a bowl of lukewarm water, before hosing it down with my garden hose, whereafter it was dried out indoors and reinstalled in the tube.

The primary mirror as received. Note the milky appearance due to a thin layer of fine dust on its surface.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

A sudsy mirror.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

There we go; a nice clean mirror ready to reinstall in the tube.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The mirror was centre spotted (which came as a relief) and I noted its thickness to be 30mm, so just over an inch. Thus, it is acceptably thin and should cool off in a reasonable amount of time.

The telescope came with a very smooth dual speed (10:1) Crayford style focuser, a feature I was to learn to greatly appreciate, as the reader will discover shortly.

The Revelation dual speed focuser; an excellent addition to an economical telescope.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Collimation was very easy to perform using the oversized knobs on the rear of the primary cell, as well as using a small Philips screwdriver to make the appropriate adjustments to the secondary.

The oversized knobs on the primary make precise adjustments child’s play. The previous owner installed stronger springs to better hold the cell in place.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

An inexpensive SkyWatcher laser collimator whipped the optics into line in a matter of seconds. Later I removed the secondary mirror for inspection and noted no coating issues with it either. I measured its minor axis to be approximately 70mm so a very respectable linear obstruction of the order of 23 per cent. Not bad at all!

Movements on the lazy suzan mount were smooth and easy to execute, both in azimuth and altitude; certainly adequate to the intended purposes I wish to use the telescope for.

I fitted the instrument with my right angled 8 x 50mm finder borrowwed from ‘Octavius’, my 8 ” f/6 Newtonian reflector. Whatever others claim concerning the curse of acquiring a new telescope to play with, the weather remained fair for me that evening, with the promise of a clear sky, albeit in summer twilight. So I readied the instrument and set it outside to acclimate as sunset slowly approached.

The 12″ f/5 Newtonian awaiting maximal darkness on the evening of July 8 2017.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

At 23:00 BST, I managed to track down the bright summer luminary, Vega, in bright twilight and excitedly aimed the telescope at it, using a power of about 190x initially. To my great relief, the star focused down to a very tight disk with intense diffraction spikes from the secondary support. The image was remarkably calm and I then racked the eyepiece inside and outside focus. Again, I was very impressed at how the defocused Fraunhofer diffraction pattern presented itself. The optics looked nice and smooth, being virtually identical inside and outside focus. Inserting a quality, 6mm orthoscopic yielding 254x, I re-examined the star in the same way. Again, I was very impressed at how the star test was shaping up. I noted a touch of overcorrection; but it was very minor. There was no visible sign of astigmatism (phew!) or ugly zones. This was indeed a good, large, mirror; no, a very good mirror; in fact, as I recall, absolutely astonishing for the low price I paid for it!

As the sky grew a bit darker, I swung the telescope over to Epsilon 1 & 2 Lyrae, which the finder was just able to pick up in the bright, twlit sky. Leaving the 6mm orthoscopic in situ, I was delighted to see that it rendered a textbook perfect split of all four components. From there, I moved the instrument westward into Bootes and centred Epsilon Bootis (Izar) in the field. Refocusing slightly (it has a lower altitude afterall), I was again rewarded with an excellent image. This tricky, colour contrast binary system can elude telescopes if the seeing is not up to scratch. It was around this time that I reached for my trusty Baader single polarising filter, which imparts a slight darkening of the twilit sky and increased the contrast of the stellar components without imparting a colour shift. The filter improved the image still further by reducing irradiance, I thought. Indeed, I recalled that the previous owner had also learned this trick whilst observing Jupiter with the telescope, so he was a convert to using filters on bright objects too!

Feeling more ambitious, I turned the 12” reflector on Pi Aquilae now positioned low in the south southeast; an interesting binary system with roughly equal magnitude components separated by about 1.5”. Well, the instrument made light work of the system; both stars focusing down to beautiful, round buttons at 254x. Finally, at around 00:15 BST (Sunday), I swung the telescope up the sky once again, where the difficult Delta Cygni was now showing in a darker sky. Again: astonishing! The telescope made very light work of picking off the faint companion set beside the comparatively bright primary. The image was wonderful and calm; a fine night to begin my adventures with this large telescope. Alas, there it had to end, as I had to rise early the next morning, but I retired from the field confident that I had an excellent telescope and one that would assuredly be put to good use in the coming days.

Monday July 10 2017

Time: 16:30 BST

After an afternoon of drizzly rain, it stopped for a wee while allowing me to perform a high power daylight test to the telescope. With a very overcast sky, the temperatures had stablished so I was assured of a good image of a relatively nearby terrestrial target. Coupling a 2.25x Barlow lens to the 6mm ortho yielding 570 diameters, I focused on the topmost boughs of a horse chestnut tree adorned in its full summer foliage and located approximately 80 yards distant. Focusing carefully with the fine focuser of the telescope, I was greeted with a beautifully sharp image of the leaves, with all their minute imperfections being made manifest before my eye. 570x is very close on 50 x per inch of aperture and it passed this daylight test with flying colours. Still, I was quite unprepared for what I experienced the following evening.

Tuesday, July 11 2017

Time: 22:50 BST

Seeing: very good (II), partially clouded over again after a rather clear evening.

I began the evening with a star test on Vega as before at 254x, the result of which was as good (if not better) than the results obtained on Saturday last. Very slight overcorrection noted. Nothing else to report. Polariser used to darken the sky a bit.

23:15 BST: Epsilon 1 & 2 Lyrae perfectly split at 253x. Cranking up the power to 570x yielded similar results. Stars tiny and round; very well corrected optics.

23:20: Ditto for Epsilon Bootis at 570x. Excellent split. Beautiful stellar diffraction images at these uber high powers. Amazing!

23:40: Delta Cygni. Wonderful split at 570x. More turbulence witnessed at this power but the image was mighty impressive. Stars remaining, tiny and round.

Wednesday July 12 2017

Time: 00:10 to 00:20 BST

Temperature: 10C

Seeing: remaining excellent (I/II)

Moved the telescope over to Lambda Cygni, a 0.9” pairing of white stars well positioned very high in the sky. At 254x, the system was well resolved. Then the power was increased to 570x and the image rexamined. Wow! I had never seen the system so clearly and so easily at a glance. The stars are orientated north to south, effectively perpendicular to the direction of drift!

 

The experience affirms the superiority of aperture under good seeing conditions. What a magnificent telescope I have in my possession!

 

 

The following evening was also clear. Details below:

 

Time: 23:45 to 00:15 BST (July 14)

Plotina(left) and the 12″ f/5 field tested side by side.

 

Temperature: 13C easily noted as the midgees were more numerous tonight than the cooler night of last night.

Seeing: III/IV much more turbulent than the perfection of last night

Instruments: 130mm f/5 Newtonian & 305mm f/5 Newtonian

Targets: Epsilon 1 and 2 Lyrae: split in both instruments but aesthetically more pleasing in the smaller instrument (powers employed 185x and 253x, respectively)

Epsilon Bootis: Not reliably seen in the larger instrument at 250x. Only a swollen seeing disk with maybe a hint of a companion under brief moments of improved seeing.

Companion was clearly seen in the 130mm instrument and aesthetically more pleasing at 185x

All absolutely normal.

What a difference a night maketh!

After a week’s vacation to the southwest of Scotland, I was able to resume my testing at home.

Sunday July 23 2017

Time: 23:45 BST

Instrument: 12″ f/5 Newtonian

Seeing: Appears excellent once again (I/II), quite a bit of cloud, clearing slowly.

00:00 BST (local midnight July 24)

Had a quick look at 78 UMa at 570x but failed to resolve this 0.8″ system now about half way up the northwestern sky. It is considerably lower in altitude than Lambda Cygni though. Will stick to Lambda Cygni.

00:18: Finally cleared up, but still quite hazy. Managed another excellent split of this system this evening. Execllent definition at 570x. System followed through several fields. The addition of the fine focuser is a godsend. Very useful addition!

This is the second time in 12 days that I’ve managed this subarcsecond pair!

Therein lies a project; to ascertain, through actual observation, the frequency of such nights that are available for the 12 ” to do this kind of high resolution work at this location.

00:50; went out to reexamine the system and still very well resolved!

General Commentary:

As it so happens, Lambda Cygni is Astronomy Now magazine’s Double Star of the Month (August 2017 issue  pp 86). This is what astronomer, Bob Argyle, says about the system;

In 1842, using the new 15 inch refractor at Pulkowa, Russia, Otto Struve noted that the star was a close and very unequal double star. The companion (B), some 1.5 magnitudes fainter than the primary, was found in position angle (PA) 107 degrees (east southeast) and at a distance of 0.7 arcsecond. Since then, the companion has moved retrograde to PA 5 degrees (almost due north) and the separation is near one arcsecond………B is easily seen though not so easily measured with the 20cm refractor at Cambridge; a measurement last year put B about 5 degrees behind the ephemeris, which is derived from the 391 year orbit of Wilhelm F. Rabe(18931958).

pp 86

My observations match Argyle’s very well. That it can be monitored with a 12 inch f/5 Newtonian shouldn’t surprise those who have followed my work over the years. Having enjoyed tremendous success with both a 20.4cm f/6  Dob (which has split this system but not nearly as convincingly) and a smaller, 13cm f/5 ultraportable Newtonian (pictured above), I was never in any doubt that the larger instrument would deliver. But to my knowledge no one has addressed the frequency with which this observation can be made with a 30cm aperture at this location. My hypothesis is that it is significantly more frequent than is commonly reported in the literature(or on forums). I do not, however, consider my location to be special in any particular way.

While I would concede that a large aperture classical refractor, mounted on a good equatorial mount, would be the ideal instrument for measuring this system, my observations suggest that the 12 inch reflector shows it more easily, supporting my previously stated maxim: ‘eye seeth afore I measureth.’

Monday, July 24 2017

A set of Bob Knob’s was fitted to the secondary of the 12 inch, thus facilitating quicker collimation in the field.

Bob’s Knobs replacing the generic screws on the secondary.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Looking good tonight for clear spells.Fingers crossed!

The 12 inch awaiting darkness.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Time: 23:20 BST

Temperature: +15C

Seeing: A notch or two down on last night. (Ant III), Clear sky, very little cloud.Midgees legion.

Marginal split reported at 570x (with polariser) but seeing disks swollen due to atmospheric turbulence. To get some perspective on this, Ant III seeing allows a good split of Epsilon 1 & 2 Lyrae in the 12 inch, but less aesthetically pleasing splits of Delta Cygni and Epsilon Bootis; again with slightly swollen seeing disks.

Will have another look shortly after midnight.

Tuesday July 25 2017

Time: 00:10 BST

System slightly better resolved; certainly to be counted as a split at 570x. Very impressive!

An Aside: 00:30BST

Had my first look at M13 with the telescope. Sky not fully dark yet but boy is it impressive at 254x! Easily superior to the best dark sky images with the 8 inch. Physics is physics afterall!

14:50 BST

Some Implications of the ‘Foot’ ‘Scope Project

One of the most important things a tester of telescopes must do is to work in an environment that allows such instruments to be properly assessed. For example, if one lives where the seeing is continually lousy, or at best, mediocre, one will consistently report that small, high quality optics beats everything else, especially on planets and double stars. This is, of course, the mantra of the refractor nut,  and it is true only insofar as what their local seeing can establish. Having said that, find out where your favourite telescope tester does his/her observing, and what the seeing is generally like there. Chances are you’ll see a pattern in their reports. It is anomalies like these that lead to much heated (and needless) debates on forums, where the sincere convictions of one individual conflicts with others, only because the air under which they live puts a ceiling on what can be achieved.

For example, a long time reviewer of telescopes provided an in depth review of the Discovery 12.5 inch f/5 Dob in the November 2003 issue of Sky and Telescope Magazine. In that review he states that big Dobs are not always the best choice for double star observing. He writes:

A large Dobsonian is not always the first choice for double star observing; the scope is often too bulky to track at the high powers necessary to split close doubles. Nevertheless, I ran some tests with the 12.5 inch PDHQ. The well known stars Mizar and Polaris were easy, as were the Double Double in Lyra. I was also able to split Alpha Herculis, which has a relatively easy separation of 4.6 arcseconds but is made somewhat difficult by the mgnitude difference (3.5 and 5.4) between its components. But despite repeated tries, I never did split Delta Cygni, an even tougher target with 2.2 arcseconds separating its 2.9 and 6.3 magnitude components.

pp 57

While there is no other indication from the same review that there was anything untoward about the optics in this telescope, what does seem odd is that he never managed to split the relatively easy pair, Delta Cygni. This would indicate to me that his seeing conditions were just not up to scratch for this task. The 12.5 inch ought to have done far better if his conditions were in any way decent. Thus, and with all due respect to the tester, reports like this must be taken with a pinch of salt.

Time: 22:45 BST: Looking promising again tonight! Yeehaw! I have just come in from a quick test on Epsilon Bootis with the 12 inch telescope and managed an excellent split at 254x. Midgees biting like mad though. More cloud tonight but some good clear spells presenting themselves.

Temperature: 14C

 

I spent some time earlier dipping into the interesting chapter 11 of the 2nd edition of Observing and Measuring Double Stars (Argyle R.W, ed). I have mentioned the author’s work before; a one Christopher Taylor, who has been observing  ultra tight binary stars from central England since the 1960s using a 12.5 inch F/7.04 Calver reflector. On page 135 Taylor mentions something of great interest to me;

It is probably in part the lack of such training and consequent failure to distinguish the seeing blur( the gross image outline) from the still visible Airy nucleus which is responsible for the persistent myth that seeing limits ground level resolution to 1 arc second at best, and is certainly the origin of some of the more spectacularly absurd figures one sees quoted for alleged image size.This author’s experience of typical conditions at a very typical lowland site may be of some interest in this context: using a 12.5 in Newtonian at 400 feet elevation (130m) in central England, an equal 0.75 arc second pair (such as η CrB in May 2000) is steadily separated by a clear space of dark sky at 238x in seeing of only III to II (Ant.)

pp 135

You don’t say!

Time: 23:41 BST: After waiting for a suckerhole to appear in the clouds, I finally got a glimpse of the system (it’s dead easy to find!) for about 90 seconds, but enough to witness yet another clean split of the stars. Power 570x. Much better than last night. Steady image with plenty of dark sky separating them.

n = 4

I believe Taylor is telling the truth. My observations so far match his.

I would warmly encourage others to participate in this high resolution experiment. A 10 or 12 inch Dob should do the trick, and don’t worry about how much the instrument set you back. As far as I’m concerned the cheaper the better!

Vere dignum et iustum est.

00:48BST

If you’ve been following my blogs, you’ll be well aware that I’ve been chasing Lambda Cygni for a few years now. The 8 inch f/6 Newtonian has resolved the pair well, but only on the best nights (Ant I), but the 12 inch f/5 seems to show this spectacle of nature routinely at Ant III or better. I think Taylor is on to something here. Allow me to couch what I think he’s saying in the simplest possible terms:

With a modest gain in aperture, separating these stars is easier because there will always be moments in fair to average seeing conditions for the larger aperture to split them. It’s pretty much analogous to the idea that a larger aperture shows planetary details better even in fairly rough seeing because nature provides opportunities to let those details pop into view, if only for a few fleeting moments. Shimples!

Wednesday July 26 2017

Doing the night shift ken

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Time: 23:18 BST

Seeing; Ant II, partially cloudy, brisk westerly wind

Temperature: 13C

Comments: If a job’s worth doing, it’s worth doing fully and completely.

n = 5. Good split at 570x. Image breaks up momentarily but comes back together often enough to see both components clearly. Making more observations in the next half hour or so.

Time: 23:41 BST

System revisited and easily resolved under tonight’s conditions.

Thursday, July 27 2017

The results that I have obtained thus far can’t be exceptional. They must be part of a broader aspect of natural behaviour Thus, there must exist many such places where larger aperture Newtonian telescopes have done the same thing. And since this blog is about the performance of Newtonian reflectors in particular, I contacted Mark McPhee, an amateur astronomer based in Austin, Texas, USA. Mark has been observing and imaging subarcsecond pairs with both his 8″ f/6 Orion (XT8i) Newtonian and a 15 inch f/4.5 Newtonian and produced this amazing post back in December of 2016.

Quite clearly, Mark has provided powerful evidence that subarcsecond pairs cannot just be observed but they can also be effectively imaged. Many of Mark’s targets, of course, go considerably deeper than anything I’ve done in this blog. I asked Mark to provide an overview of what his typical conditions are under which he performs his work. This is what he said:

I gather that my seeing is very good here compared to that for most. In the warmer months (which is most of the year here) I can get a good number of very good seeing days in. I often rate the seeing as at least a 3 out of 5 with a good sprinkling of 3+, 4- and bone fide 4’s in the mix. So, the images I presented are fairly representative of what I see and match a 3+ out of 5 on average. A seeing of 2 or less would likely not be feasible for imaging (or splitting) these challenging systems.

This agrees with the observations I have made thus far regarding Lambda Cygni. But he thinks his conditions might be a wee bit special. I respectfully disagree  (n=?). I also believe that if other amateurs tested their large Dobsonians (up to about 15 inches), many more would discover their power to resolve such pairs.

Mark has since gone from strength to strength. He writes:

I am in the process of compiling about 30 double star measures of rather difficult pairs for my first solo JDSO submission–this will contain a detailed description of my methodology.

Fondest congratulations Mark! I hope it will the first of many such submissions!

Nota bene: Mark has also posted work done with his XT8i. You can see some of this work here.

Further thoughts on the Newtonian in respect of high resolution, double star astronomy

Taylor’s essay in chapter 11 of the aforementioned book states that he has done all his subarcsecond double star work in the open air, that is, there is no observatory. My work is also conducted entirely in the open air.

Taylor’s analysis, reproduced in my blog here, advises that this kind of work is unlikely to be successful at < f/5 relative apertures. This author’s work is in disagreement with that conclusion, as is McPhee’s phenomenal results highlighted earlier. My own work utilises only a Barlow lens (2.25x) boosting the geometrical optical train from f/5 to approximately f/11.3. Furthermore, the use of a Paracorr (or other coma correcting optics) would also help correct the field of view for this type of exacting work. Taylor’s analysis never took any of these considerations into account and so his f ratio restrictions can be somewhat relaxed. Thus, I can see no theoretical barriers to owner’s of f/4 Newtonian systems with good, properly collimated optics. Why not give it a go?

Friday, July 28 2017

Well, I’ve reached my first milestone with this telescope; I have (very probably) used it more than the previous owner has lol!

Am I happy with it so far? You bet! To be honest I’m rather in awe of how good the optics are. As I have said previously, I have always suspected that the chances of acquiring a good, mass produced telescope in this aperture class is rather less than for smaller telescopes, such as an 8 inch. The reason I believe this is the case is that the amount of effort needed to get a good mirror must scale with the area of the surface to be worked. And there is plenty of anecdotal evidence to support that claim. How many times have we heard of individuals purchasing a telescope of this size only to be disappointed with the star test it serves up? And there is no shortage of folk who decided to have the primary mirror refigured or some such. From the observations I have made, I am relieved to say that I have absolutely no intention of upgrading the primary. I do however plan to do what I did with my smaller Newtonians, namely to get the mirrors coated with HiLux enhanced coatings, as I have been very pleased with how the others have turned out.

After talking with Orion Optics UK, I decided on replacing the secondary mirror with a slightly smaller unit; in this case a 63mm minor axis diameter. That’s a little bit smaller than the existing 70mm flat but not enough to require a lower profile focuser or some such. The new flat will give a 20.6 per cent linear obstruction, so very respectable indeed for all round work. I intend to get the primary recoated later in the autumn.

The original flat elliptical mirror in its plastic housing.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The replacement dovetails nicely with a turn in the weather. After a longish spell of fair evenings, we are now sat under a big, ugly low pressure system delivering torrential downpours; so not good for hauling out a large telescope like this.

What a roller coaster ride it’s been so far. Going forward, I determine to accept nothing on faith, or received wisdom, but only to see everything with my own eyes.

Newtonians have been so very kind to me, helping me to take my observing to new heights of sophistication. For many years I dismissed their powers largely for trivial reasons. Sure, they don’t look quite as fetching as a pretty refractor or compact catadioptric, but it’s the views that count. My environment clearly permits me to exploit telescopic aperture in a productive way, unencumbered by physical, geographical or psychological boundaries. And should I get an opportunity to observe while the new flat is being fitted, I’ll be reaching for Octavius, my wonderful 8″ f/6 Newtonian, the instrument that most powerfully catalysed my transition from small refractor culture. For more than a decade I succumbed to the charms of the object glass, being exceedingly zealous to promote their various attributes. Indeed, it is all too easy to engineer a scenario where the little ‘peashooter’ ‘scopes always win. Try comparing a 4 inch refractor to a 12 inch reflector say, while the latter is still acclimating and you’ll see what I mean. Newtonians teach you to be patient with telescopes, to figure out how best to tame them. And when you do that, a whole new Universe is set before you.

My dream ‘scope: Octavius, a simple 8″ f/6 Newtonian reflector.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Saturday, July 29 2017

There will be a slight change of plan regarding the secondary mirror. I have decided just to have it recoated. Afterall, the existing mirror works perfectly well and the central obstruction is already acceptably small. The better coatings will increase light transmission to the eye and help increase overall contrast in the image by scattering less light/lowering irradiance. The primary will follow suit later this year.

Monday, July 31 2017

Secondary despatched to Orion Optics UK.

Haste ye hame!

Time: 23:00BST

Seeing: very good but not perfect (Ant II), slight westerly breeze, some breaks in the cloud.

Instrument: 20.4cm f/6 Newtonian reflector, 450x, polariser

Octavius; carrying on the subarcsecond project.

Comments: Continuing this project with Octavius, I was delighted to get a convincing split of Lambda Cygni again this evening under conditions which I did not think would be favourable enough for the 8 inch instrument to pull off. Perhaps it was my recent training with the 12 inch or my lack of diligence in following up this system with the smaller instrument under less than ideal conditions that led me to conclude that it can only be seen in Ant I. Clearly it can be resolved in Ant II. Thus, using inductive reasoning we have n = 6.

Time: 23:50 BST

With a good clear spell now developing, I decided to have another look at the system with the 8 inch. 450x is a good magnification for this kind of work, but even at this power, the system remains small and tight, so I had the idea of boosting the power still more; to 600 diameters using a not too frequently used Vixen 2mm HR ocular.

Well, it certainly improved the situation! The pair were more convincingly separated at this power than at 450x.

Ocatvius certainly has excellent optics for an 8 inch ‘scope! 600 represents 75x per inch of aperture; very good indeed under field conditions.

Thus, in all future observations of well placed subarcsecond pairs with this instrument, I will utilise this ocular as it has clearly proven its worth tonight.

System reobserved just after local midnight at 600x. Split once again confrmed.

A rather specialised ocular: the 2mm Vixen HR.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Tuesday July 2017

Time: 22:45 BST

Instrument: 20.4cm f/6 Newtonian

Seeing: III, more turbulent than last night, good transparency.

Comments: After a day of torrential downpours with some sunny spells thrown in for good measure, the sky cleared at sunset and I was able to perform another observation. Tests on both Epsilon Bootis and Delta Cygni both revealed their companions at 200x but not as well as last night. Applying 600x to the instrument on Lambda Cygni revealed a very complex diffraction pattern. One can easily discern that the system is duplicitous but no clean split was forthcoming. Out again for another look.

NB. The Vixen HR series are not threaded to accommodate filters. What a bummer. Such an expensive ocular without this basic provision!

Time: 23:07 BST

More cloud encroaching unfortunately. Time to pack up methinks!

Time: 23:17 BST

Hold your horses! Had another look; seeing improved and a split recorded at 600x so n = 7

Comments: Not that unusual for seeing to improve during a vigil. Both stars steadily held on and off through a couple of fields.

Explanations: slight gain in altitude or more thorough passive cooling of the optical train; more likely the former as the system was first examined earlier tonight than last night.

Heavy dew now; so need to pack up.

Time: 23:27 BST

Couldn’t resist one more gander lol. Both stars cleanly resolved between intervals of turbulence, where the image breaks up. This is so cool!

n = 7 stands.

Note tae sel’: Will attempt to refrain from making observations before 23:00 local time (22:00 UT) at least for the next few weeks.

Thursday, August 3 2017

Go to the ant, thou sluggard; consider her ways, and be wise

Proverbs 6:6

I was reading through my Bible this morning and the proverb above just jumped out of the page. It’s amazing how Scripture does that eh?

What an extraordinary run of results so far! It appears I can manage a decent split of this pair any time the seeing is fair to good and as long as I use decent telescopic aperture.

All sorts of questions popped into my head, such as;

  1. What is really meant by a subarcsecond night?
  2. Are the results obtained thus far the result of special seeing conditions?
  3. Is the complete lack of such sustained observations of this kind on the various double star fora attributed to good old fashioned laziness?

Like I said, I strongly suspect question 2 is false, as I don’t really think that my location is an isolated system.

But what about question 3? How many folk really understand the nature of the environments in which they regularly observe? Would more people report the same had they enough diligence to do the necessary work? I dare say they would!

The newly coated secondary should be with me towards the end of next week so I’ll be able to resume testing with the foot ‘scope.

Time: 23: 25 BST

Gaius(laevo) et Octavius: fratres aeterni.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The forecast predicted a mostly overcast evening, but as I’ve explained many times before, there will always be the odd break now and then. I decided I’d be ready early this evening, fielding both Gaius, my trusty 80mm f/5 achromatic, as well as Octavius (20.4cm f/6 Newtonian) from about 20:30UT.

I enjoyed a few favourite double star targets with Gaius as I waited for time to pass after 22:00 UT and at 22:25UT I finally got my chance to examine Lambda Cygni at 600x with Octavius. I can report yet another clean split so n = 8.

By 22:37 UT it had totally clouded over, so no further tests could be made.

I suppose the old adage is true: good things come to those who wait. Or how about, chance favours the prepared mind?

The system is very well placed now for far northern observers so if you have a good medium sized Dob, give it a go. Chances are you’ll see it regularly too!

For those further south, why not pick another candidate system just below the 1″ threshold. What have you got to lose? It’d be fun discovering new stuff eh?

Or do you have something to hide? I wonder!!

Friday, August 4 2017

I am hoping as many people as possible will participate in this project to get to know their local conditions better. Surely such knowledge is valuable! Of course, there will be places here and there that won’t yield these results (or at least nearly as often), yet in truth, of all the places I’ve observed from for any length of time here in Scotland, only two locations proved poor quite a bit of the time (and one of them includes my previous abode in the village of Kippen just 7 miles away).

Nor do I claim any credit for myself. This was Christopher Taylor’s revelation and therefore his ‘discovery.’

Away for a short weekend vacation. See you guys n’ gals next week.

Monday, August 7 2017

Tiberius (laevo) et Octavius: fratres aeterni.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Time: 20:20 UT

Another night of tests coming up. Good clear evening, ken. I felt like Hulk Hogan fielding Tiberius,  my 5 inch f/12 refractor, a top quality long focus instrument. Weighing in at 40 pounds (OTA only), it’s a beast of a ‘scope. Accompanying it is Octavius.

Time: 22:15 UT

Seeing: Very good (II), some light cloud moved in but large swathes of sky remaining clear. Moon low in the south southeast.

Temperature: 12C

Lambda Cygni examined in both instruments.

5″ f/12 refractor: Unresolved but strongly notched at 429x and 572x

8″ f/6 Newtonian: Easily resolved at 600x, so n = 9.

The limited aperture of the refractor is plainly on display. The 8 inch reflector is far more suitable to this kind of work than a 5 or 6 inch refractor.

Ye cannae change the laws o’ physics captain.

Don’t you just love debunking myths.

Tuesday, August 8, 2017

Time: 23:25 UT

System reexamined and once again split at 600x.

Also studied Delta Cygni (now at zenith) at 200x with the 8 inch reflector both with and without the Baader single polariser. I can report that the filtered image gives a more aesthetically pleasing image of the companion. The stars are tighter pinpoints. Very refractor like! This is a marvellous (and relatively inexpensive) little tool for the reflecting telescope.

Wednesday, August 9 2017

Time: 23:17 UT

Temperature: 13C

Seeing: A notch down on last night, slightly more turbulence (II/III). Some rather stubborn cloud moved in, dousing the instrument in a light shower of misty rain lol. Thankfully all optics were covered! Once the cloud moved away, another observation was made.

Instrument: 20.4 cm f/6 Newtonian

Comments: Rather late to the table this evening, owing to considerably more than expected cloud cover. Lambda Cygni resolved unstably this evening at 600x. Diffraction pattern more messy, but the image does settle down frequently enough for its full duplicity (i.e. two non contacting stars) to be plainly discerned.

n = 10

Time: 00:03 UT

System reobserved and split confirmed in the same manner as earlier. n = 10

Time: 20:45 UT

I can hardly believe it’s only been a month since I started this blog. Seems a lot longer than that!

I received news today that the secondary for the the 12 inch will be with me early next week, so slightly later than I previously envisaged. But Octavius is doing rather a good job don’t you think?

Yet another clear night this evening and the 8 inch has been set up to do another night’s work. Looking good.

Dream machine, ken.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Time: 22:30UT

Seeing: II/III. Almost a carbon copy of last night but with no cloud.

Instrument: 20.4cm f/6 Newtonian

Temperature: 12C

Comments: Started observing the star at 22:00UT but was unsuccessful for quite a few minutes. I found it hard to focus tonight and checked collimation of the optical train, making a slight adjustment (which probably would not have made much difference). After a few more unsuccessful tries, I finally gave it a go at 22:30 UT and did manage a split of the components at 600x, so n = 11.

Out again for another observation.

Time: 22:48UT

Another successful split at 600x. No problem, easier this time. n = 11

Thursday, August 10 2017

Time: 23:13 UT

So another good night of work. Clearly, it’s generally beneficial to wait until the system rises as much in altitude as possible, so my earlier attempts might be reflecting this to some degree.

I am missing the sheer aperture advantage of the 12 inch instrument. My notes and mental recollections showed me how much easier it is to see the components of this sub arc second pair. They are easier to see at a glance in the larger telescope, no question about it. I just wish I had the secondary back, but I know I’m just being impatient. Silly me.

Saturday August 12 2017

Time: 20:30 UT

Champion ‘scope; Octavius.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

After a couple of cloudy and wet days, we have another clear sky here this evening.The glorius 12th! So, once again, I have fielded Octavius to continue the work until the 12 inch is ready.

Time: 22:03 UT

Instrument: 20.4cm f/6 Newtonian

Seeing: Very good (II), wonderful transparency. no cloud; a beautiful evening!

Temperature: 12C

Comments: System split at 600x. No problems tonight. n = 12. A telescopic meteor darted across the field while the observation was being made; a Perseid of sorts!

Away to briefly watch for more meteors.

Tuesday, August 15 2017

Time: 20: 22 UT

After another couple of overcast nights with no prospect of getting an observation in, the sky looks good again this evening. Alas, the secondary has not yet arrived back, but I have been assured that it will be with me tomorrow. So, I call upon the services of Octavius for a last time.

I have been reflecting a little on the results I have thus far obtained. In essence they demonstrate a very basic tenet of telescopic astronomy; a tenet accepted by all previous generations of amateur astronomer but less so in this one for reasons I am acutely aware of; that aperture rules provided the conditions are good enough to exploit those apertures. Indeed, this work fits seamlessly with all of my other work. For example, a 130mm f/5 Newtonian  proved superior on all targets to a 90mm apochromatic refractor (which was very embarrassing). The 8 inch reflector proved crushingly superior to a very high quality 5 inch refractor on all targets. Indeed, the former will outperform any refractor up to at least 6 inches (I’ve actually tested it against a 160mm triplet and found the Newtonian better in some respects and at least its equal in others). These are true and expected results because my environment can clearly handle moderate apertures very well. Indeed, I am more than happy to test any refractor in the aforementioned size range against my 8 inch f/6 Newtonian if the reader is interested in delivering a unit to my home. I suspect though that I’ll not have many offers lol. Denial and hubris, no doubt, are key factors here. But the offer is there should any one of you wish to take me up on it.

Will the 12 inch do likewise to my 8 inch? Judging on what I’ve observed so far, I can’t think of a single reason why it wouldn’t, but those tests will continue in due course.

True darkness is upon us once again! And what an autumn it will be for the 12 inch reflector!

Time: 21:33 UT

Temperature: 12C

Seeing: Excellent ( I/1.5), beautiful clear sky, very gentle southerly breeze

Instrument: 20.4cm f/6 Newtonian

Comments: Lambda Cygni easily split once again at 600x. Indeed, it was so easy this early on that I had a go at 78 UMa (easily found in the Ploughshare), which has a 0.8″ companion. At 21:40UT I managed to see this companion at 600x on and off as it drifted through the field! That’s very encouraging to say the least! Though considerably lower in the northwestern sky at this time, the excellent seeing allowed me to glimpse it!

n = 13.

Away to have some fun with the deep sky now. Talk again soon.

Wednesday, August 16 2017

Time: 19:48 UT

Well, the recoated secondary arrived here safely this afternoon, as promised. They did a great job on the mirror. Looks flawless. There was a slight hiccup with the original mirror holder though. If you look at the image posted Friday, July 28, you will notice that the original mirror was held inside a plastic holder. The technician at Orion Optics informed me that while he was prizing the flat out of the plastic(read cheap) structure it actually fractured!

Shockeroonie ken !

All was well though when he kindly offered to mount the flat on one of their own secondary structures (with no additional charge). And naturally, I accepted!

 

The newly coated and edge blackened secondary on the new supporting structure.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

That was a nice gesture on their part.

Like all the other secondaries I’ve handled, I gave the edge of the mirror a coat of matt black paint before remounting it inside the telescope tube. Optics were then accurately realigned and now the instrument sits ready to sample star light once again.

The accurately measured flat minor axis is exactly 70mm, so that translates to a very respectable linear central obstruction of just 22.9 per cent.

The heavens opened in the early morning and continued all day. Still cloudy and dreich as I write.

Thursday, August 17 2017

Time: 21:34 UT

Seeing: Very good, II, sky cleared at sunset after another day of torrential rain.

Temperature: 13C

Comments: A race against time this evening, as more heavy showers are forecast overnight. But I had the 12 inch f/5 Newtonian maintained near ambient temperature in my dry, unheated shed. I can report a very good split of Lambda Cygni at 570x (6mm Baader classic Orthoscopic with 2.25x screw in Barlow). As reported previously, the pair of white stars are easier to see in the 12 inch than in the 8 inch. Very impressive sight!  n= 14

Now retiring the ‘scope before the next downpour is upon us.

 

An aside: As well as the other observing blogs I’ve done over the last several years in the peaceful surroundings of my home, I left it a few times in order to engage with the public on other(mainly) double star projects establishing the efficacy of other telescopes for the interested amateur. See here and here for examples. One can gauge the frequency of fair to good skies I enjoyed in recent years, which I believe strengthen the central tenets of Taylor’s hypothesis, at least at my observing location.

Friday, August 18, 2017

Time: 22:50 UT

Temperature: 13C

Seeing: IV, below average, good transparency, little cloud

Instruments: 20.4 cm f/6 Newtonian & 12″ f/5 Newtonian

Comments: companions unresolved in both instruments (600x and 570x, respectively). Turbulent, swollen and disjointed diffraction pattern.

Saturday August 19, 2017

Time: 21:15 UT

Seeing: III, blustery winds, some clear spells.

Temperature: 12C

Instruments: 20.4cm F/6 Newtonian & 12″ f/5 Newtonian

Comments: After another unsettled day, we got a reprieve in the late evening, so I decided to field both instruments again. Lambda Cygni pair just resolved in both instruments (same magnifications as last night) but it was that little bit easier to discern in the larger instrument, despite the choppiness of the atmosphere. n = 15.

Wednesday August 23 2017

Time: 20:25 UT

Say, that’s a bonnie lightbucket oot me back gairden, ken.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

After another brief vacation and a few days of inclement weather, it’s back to work again tonight. Good chance of making another observation a little later on. Fingers crossed eh!

Time: 21:45 UT

Instrument: 12″ f/5 Newtonian

Seeing: very good, II, light westerly breeze, mostly overcast with the occasional clear spell.

Temperature: 15C

Comments:  A braw evening. Target beautifully split with the 12 inch at 570x. The combination of the 6mm classic Baader orthoscopic and 2.25x screw in Barlow proved much more comfortable to use in the field than one of those fancy schmancy Vixen HR thingmies.

n = 16.

Time: 22:00UT

Target examined once more and full duplicity easily discerned at 570x.

This is a verifiably real phenomenon. How many times must I repeat it to demonstrate its veracity? This high resolution target is accessible in the foot ‘scope any time the seeing is fair to good. Why should my observing location be privileged?

I dinnae ken.

Time: 22:45UT

Overall Conclusions:  The Taylor hypothesis appears to be correct. I got this from the essay he wrote in the aforementioned book and not from anyone on the internet. Taylor could state this as real because he made the observations to demonstrate its validity, as did I. I am astonished and a little upset that this has not been reported by those who claim to have the most experience.

This is where the blog ends. But I will come back to this occassionally with updates.

I would encourage others in possession of moderate aperture Dobsonians to test this work for themselves. Make sure your optics are accurately collimated and thoroughly acclimated before conducting such tests. Good luck and thanks for reading!

Update: August 29 2017

Lone Ranger….ken

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Two more sightings made on August 26 and August 29 (consecutive observations). Both with 12″ f/5 instrument at 570x.

n = 18.

Update: August 31 2017

Two more good nights of observations made (30th and 31st August) and two more clean splits to report with the 12 ” f/5 reflector at 570x.

n = 20

Update: September 5 2017

Two further consecutive positive observations to report with the 12″ f/5 Newtonian made at 570x on Friday and Saturday, September 1 and 2.

Thus n = 22.

Satis.

 

De Fideli.

 

Test Driving the SkyWatcher Skyliner 200P

A Work Dedicated to Brian Carter

 

The cure for unobtanium is a good dose of speculum!

Here I shall provide an in-depth evaluation of the SkyWatcher Skyliner 200P; an 8 inch ( 203mm) f/6 Newtonian reflector.

Friday, January 30 2015: The telescope was ordered from Rother Valley Optics, UK. The complete telescope was purchased for £288, inclusive of delivery to my door. I chose this telescope owing to its almost universal acclaim by amateur astronomers of all levels of experience, from novices through to seasoned veterans. I was interested in getting something larger and more powerful than the most excellent 6″ (152mm)  f/8 model but  not something that would be too large and cumbersome. Many literary sources discussing Newtonian optics recommended as slow a mirror as one could get away with. As a purely visual observer, I was pleased to hear that SkyWatcher were offering their 8-inch Dob at a respectable f/6 relative aperture; a good compromise between portability, functionality and performance with a modest eyepiece collection.

An inexpensive Skywatcher laser collimator was purchased at the same time.

Monday, February 2: The telescope arrives in two boxes; one containing the telescope and various accessories and the other containing the flat-packed Dobsonian base. The telescope was presented in excellent condition, as were the accessories, but it was quickly discovered that the lazy Suzan rocker box supplied with the telescope was actually for the smaller 6 inch model. Oh dear; never mind!

A quick phone call to the retailer was enough to arrange for the delivery of the correct size base and the collection of the 6 inch base.

23:00h: A set of tube rings and a dovetail plate were found for the telescope and I was able to attach the instrument to my heavy duty SkyTee Alt-Azimuth mount. Turning to Jupiter, it was easy to see the optics were quite a bit out of alignment but I was taken at the sheer brightness of the planetary image. Star testing confirmed that the optics were mis-collimated.

The simple but sturdy focuser on the telescope can accommodate both 1.25 and 2″ oculars. The package came supplied with an 8x50mm straight through finder- always an impressive addition in my opinion.

Good but sturdy; the focusing unit on the Skyliner 200P

Good but sturdy; the focusing unit on the Skyliner 200P.

 

 

 

 

 

 

 

 

 

 

 

 

The innards of the optical tube were painted matt black and the parabolic primary mirror looked immaculate with no sleeks or flecks of dust/paint. Very nice indeed! Two eyepieces were supplied with the instrument; a ‘wide field’ 25mm focal length ocular delivering 48x and a higher power unit giving enlargements of 120 diameters.

The inner sanctum of the SkyWatcher Newtonian. All is well presented.

The inner sanctum of the SkyWatcher Newtonian. All is well presented.

 

 

 

 

 

 

 

 

 

 

 

 

 

Tuesday, February 3: The laser collimator arrived this morning and I quickly got to work aligning the optics. This device makes very light work out of precisely aligning the optical components. After placing the device firmly in the focuser, the secondary mirror was precisely aligned with the central spot of the primary and  then the primary was adjusted slightly to complete the collimation. This only took a few minutes to do but should make a huge difference to the images garnered by the telescope.

An inexpensive laser collimator makes collimating the instrument child's play.

An inexpensive laser collimator makes aligning the optical train child’s play.

23:30h: Seeing fair to good(Ant II-III).

With the telescope fully acclimated in -6C temperatures, I conducted a quick star test using my trusty 24-8mm Baader Hyperion zoom to confirm that the optics were properly aligned. The full Moon was easily framed with lots of room to spare at the 24mm (50x) setting of the zoom, the image being razor sharp and blindingly bright at the same time. Aiming at Polaris, I was very pleased indeed with the beautiful concentric diffraction rings either side of best focus at 150x. No astigmatism was noted with no signs of significant zones. This is a good, smooth mirror by most anyone’s standards.  In focus Polaris A was pinpoint sharp with delicate diffraction spikes consonant with a good Newtonian image. Its faint companion was easily picked off wide away.

I know; it's a Dob..... but I couldn't wait to test it.

I know I know; it’s a Dob….. but I couldn’t wait to test it.

Comparing the views of Jupiter with my 17cm f/16 Maksutov Cassegrain at~ 150x, I was very impressed how well the 8 inch Newtonian was performing. At a glance I could see finer detail than in the smaller aperture Maksutov, although the sky background in the latter was considerably darker.This could be attributed to stray light from off axis moonlight though and will require further investigation. I could also see the faint impression of the slender spider vanes superimposed on the in focus image, though after a few seconds, one could effectively ignore them and get on with enjoying the images.The brightness of the planet in the Newtonian at 150x will call for higher optimal magnifications to be pressed into service in due course.

Turning the telescope on Iota Cassiopeiae, the instrument was able to cleanly resolve the three components fairly easily. Almach, now fairly low in the northwestern sky was beautifully rendered, the golden and blue colours of the components coming through easily. The faint diffraction spikes around the stars were quite fetching to my eye. I don’t know what to make of them as yet.

All in all, an impressive first light for the econo-Dob.

Thursday, February 5: The replacement base arrived safely today and the 6 inch base collected. Assembly took about a half an hour. All tools were supplied with the package.

The Skyliner 200P Dobsonian telescope

The Skyliner 200P Dobsonian telescope.

 

 

 

 

 

 

 

 

 

 

 

 

18:30h: Seeing II, temperature -0.5C, clear, tranquil sky after dusk. Telescope kept outside all afternoon with optics covered. Little chance of dew as the air is still very cold and dry.

Theta Aurigae: companion easily picked off from the bright primary at 150x.

 

speculum vs speculum

speculum vs speculum

22:30h: Some low altitude cloud rolled into the valley for much of the evening while I was teaching. The telescope remained on duty throughout. Also fielded my 17cm Maksutov (acclimated) for comparison. Only a few targets visible at any one time. Seeing improved and now excellent, as judged on a very near perfect rendition  of Castor A and B through the Maksutov at 343x. I turned the instruments to Jupiter and studied the images delivered.

The winner: without a shadow of a doubt- the 8 inch f/6 Newtonian.

Both served up very fine views but the extra resolution and light gathering power of the Newtonian in these braw conditions put it comfortably ahead. An incredible amount of ultra-fine fine detail could be made out all across the planet but my eye was drawn to the high latitudes of the southern hemisphere, where a few curious white spots and a riot of linear structures quite literally jumped out at me! Where the smaller Maksutov suggested, the larger Newtonian plainly revealed.

The above was based on unfiltered observations, but I felt the icing on the cake was delivered with the addition of Al Nagler’s latest technical innovation: the Televue Bandmate BPL. It diminishes the glare around the planet, darkens the background sky and brings out all kinds of reds, oranges, yellows and whites within its enormous atmosphere. To my eye, the image at 170x with the filter was truly magnificent! I didn’t try any higher powers as there was no need to do so.

I would invite others to pull out their GSO/Synta 8 inch Dobs, spend a few minutes lining up its optics, letting it fully acclimate (I didn’t use a fan) with its cap on and comparing its views with a more ‘revered ‘scope of similar aperture.

To the rich man I speak: the man who has ‘seen’ it all in the cold light of day.

Maybe you could buy one in for a while at least? Nothing to lose, right??

But be prepared to be shocked!

SkyWatcher Skyliner 200P: planet killer extraordinaire!

Sic transit gloria mundi!

Friday, February 6: I am still somewhat in awe of what I saw last night and no one can take that away from me. It only takes one good night to reveal the truth about any telescope, whatever preconceptions one may have had about it. Would I have been better off with a larger mirror; a 10- or 12-inch maybe? I believe that the difficulty in producing a fine mirror scales with the square of aperture. A 12 inch reflector takes four times more effort to make well compared with a 6 inch. Larger apertures may have some advantage over the 8 inch but my previous experiences with these larger Dobs suggest that I would not get as many nights where everything comes together like it did last night. Mileage counts for me.  No, the right choice was the 8 incher since I now know that it will play ball with the environment in which I reside.

I spent some time this morning mulling over old books on planetary astronomy. One choice example is Bertrand M. Peek’s tome on Jove; The Planet Jupiter: The Observers Handbook (1981 edition) in which he states categorically that “An 8 inch [reflector] is probably adequate for all purposes.”

Fred W. Price and a host of other authorities I respect, say much the same thing.

Fortune continues to smile my way, as the settled conditions look to last at least another night.

Thank goodness for small mercies!

18:50h temperature -1C, seeing II

Had the ‘scope out for a couple of hours while I was teaching. Before the Moon rose above the horizon, I managed a very competent split of Eta Orionis (1,6″) at 225x. The Great Nebula in Orion (M42) was jaw-droppingly fine; a great heaving mass of ‘chlorescent’ gas at 120x. The Trapezium stars, including the more elusive E and F components, were easily sighted.

19:30h In a race against time, I assessed its wide field capability with two of my eyepieces; a Mark III 24-8mm Baader Hyperion zoom and 40mm Erfle. Both eyepieces performed extremely well in the very forgiving f/6 Newtonian. Cruising through central Orion at 30x in a 2+ field is a joyous experience, with stars staying acceptably sharp over the majority of the field with only the extreme edges showing coma and field curvature. I noted identical behaviour with the zoom eyepiece at the 24mm ( x50) setting.

You'll need to use the supplied adapter to get 2 inch oculars like this 40mm Erfle to work.

You’ll need to use the supplied adapter to get 2 inch oculars like this 40mm Erfle to work.

 

 

 

 

 

 

 

 

 

 

Caldwell 14, the Great Spiral in Andromeda (M31), the Auriga open clusters and M35 were simply spellbinding in the telescope. I have a 8 inch f/6 doublet achromat awaiting return to its manufacturer but I can tell you this Skyliner 200P package – costing 11 times less and weighing half as much – is a much superior telescope in almost every conceivable way!

Is a 8" f/6 rich field refractor really worth it?

Is a 8″ f/6 rich field refractor really worth it?

 

 

 

 

 

 

 

 

 

 

 

 

Oh vanity of vanities!

Later tonight it’s Jupiter watching time. Away in to watch the rugger the noo.

23:30h:Smashing opening performance by England against Wales in the Six Nations championship.

Low waning gibbous Moon in the southeast. No clouds.

Seeing deteriorated a little this evening (Ant III), as judged by the appearance of slightly swollen seeing disks in Castor A and B in the acclimated Maksutov. I decided to test how fast it would take the 8 incher to come to temperature by taking it directly out from a warm indoor room to the cold of pre-midnight air at -3C ( so ~ 25 degree C swing). The optics were left covered throughout. When I returned to the telescope an hour later, the images had stabilised. That’s no surprise though, at 8.6 kilos (19 pounds) fitted with its finder, the Newtonian actually weighs less than the 20 pound Mak and enjoys a much greater area over which to rapidly radiate heat.

I again compared the views of Jupiter served up by the Maksutov (17cm) with the 20.3cm Newtonian and the result was the same; the Newtonian shows finer details than the compound, confirming that aperture wins.

I’m not really known for having great affection for Newts, but this dapper telescope has got my pulse racing.

Saturday, February 7: This afternoon I leafed through my old observing notebooks from the years 1996 through 1997. Back then I was living in the city of Aberdeen, Northeast Scotland, and enjoying my first salaried job as a lecturer at the local university. In the summer of 1996, I purchased a Celestron 8″ f/6 Star Hopper Dob and at a much higher relative cost than today. “Wolfgang,” was big and awkward, with a cheap, oversized sonotube OTA. I observed Jupiter throughout the summer and autumn of 1996 with this telescope and my drawings reveal a good amount of detail; rather similar to the details I have recorded in more recent years with my 5″ f/12 achromatic. I was very pleased with the images Wolfgang served up – it was the base that failed first – but the planetary detail revealed by my new Skyliner 200P is easily better (on all but the worst nights) than any five incher can deliver. I was puzzled by this, and it got me digging a little deeper into my notes. Turns out Jupiter was fairly low  in my sky during those years, sprinting through Capricorn (1996) and then Aquarius(1997). Now, Jupiter is considerably higher in the sky and the differences between these instruments are much more apparent. That’s one theory. Here’s another one: Maybe the SkyWatcher mirror is truly better than the one I got with Wolfgang? Can technology improve in 20 years? It is not unreasonable to think that it could.

Man and his technology!

22:15h: Sky clearing of clouds, -2C, good seeing (Ant II): One final comparison between the 17cm Maksutov and the Skyliner 200P. Target: Jove: Both telescopes serving up super fine images. The 8 inch image is more detailed though. GRS approaching the planetary limb…..cool.

23:00h: Since the conditions were quite good, I decided to push the telescope by examining the diffraction images of stars at very high powers. Using the 2.25x Barlow with the zoom, I dialed in a maximum power of 338x and examined the brilliant white pair Castor A & B. In this cold weather, the heat from your body can affect the image, especially when you place your warm hand in front of the optical train to reach for the handle. This quickly dissipates though and when you are wrapped up warm and well insulated the effects are minimised.

I was really quite impressed at how clean and together the morphology of the Airy disks presented at these high powers. The diffraction spikes are quite charming and have an aesthetic grace all of their own. I have a very good mirror; a mirror that will surely see a lot of use over the months ahead.

Monday, February 9: With the moon now out of the evening sky, I spent a few minutes yesterday evening enjoying some dark, transparent skies with the Skyliner 200P. Using the low power (50x) setting on my zoom, I turned the telescope towards Cassiopeia now nearly overhead, and spent a few minutes drinking up the views of a few favourite open clusters including NGC 457 (with its ET eyes staring back at you), M103, M52 and a real corker: NGC 7789 which, at higher powers (75x), resolves into a plethora of faint stars. The traction on the mount is quite good and it’s easy to find the ‘sweet spot’ for most any application, from low power scanning to tracking planets and smaller deep sky objects at higher powers.

The SkyWatcher model in my possession probably has a similar mirror to the US branded Orion XT8 Dobsonian. US-based telescope reviewer, Ed Ting, has very interesting things to say about it here:

“It’s not a Zambuto,” he says, but it’s “shockingly good!”

How true!

These telescopes have been used to great effect by very well established observers on both sides of the pond. Dr Paul G. Abel, a professional astronomer and BBC Sky at Night presenter, uses the same model as my own – albeit on a motorised equatorial platform –  to make all his detailed observations of the planets. I contacted Paul to enquire about whether he had any modifications done to the optics. He told me he had not and saw absolutely no need to do so. A true draftsman, his portfolio of work is of the highest quality.

Arizona based astronomical artist, Jeremy Perez, needs no introduction in amateur astronomy circles. Using only an XT6 and XT8, Perez provides first rate illustrations to all the major astronomy magazines including Sky & Telescope, Astronomy and Astronomy Now,and has contributed to several major books on the subject of astronomical sketching. In addition, Jeremy maintains an excellent website where his versatile work with the XT8 is clearly demonstrated. Worth checking out I’d say.

What inspirational blokes we have here!

21:45h After enjoying some gorgeous views of M36, M37 and M38 at low and moderate powers, I turned the telescope to Jupiter, not yet at an optimal altitude, and was delighted to see that a satellite transit is currently underway. Will report back again later.

23:15h:

Me drawin's

Me drawin’s

 

 

 

 

 

 

 

 

 

 

 

 

Seeing wasn’t great tonight (Ant III mostly) and it was a bit on the breezy side, which made the image shake a wee bit. Fairly mild (+5C) though. I decided to keep magnifications down at 150 diameters. I followed the eclipse until it reached the middle of the disk and then noticed the GRS had reappeared. A fantastic experience!

Pure dead brilliant!

Geein’ it laldy!

 

 

 

 

 

 

 

 

 

 

 

 

Thursday, February 12: On family vacation until next week.

 

Monday, February 16: My short time away from this telescope got me thinking about its enormous potential. As it is, the Skyliner 200P is an excellent general purpose instrument; a veritable ‘diamond in the rough’. Yet, it can be improved still more and with only a modest additional investment. The reflectivity of the mirrors(worst case scenario) is ~87 per cent, so combined produce an overall light gathering power of 0.87^2 or 76 per cent. Light loss due to the area of the secondary mirror reduces this by just a few more per cent.  That’s  not bad at all:- still significantly more light gathering power than a 6 inch refractor but with greater resolving power.

Curiously, there are services available to increase the overall reflectivity of both mirrors to 97 per cent. For example, Orion Optics UK offer their Hilux coating which would bring its light gathering power into line with a similar sized refractor and maintain this ultra-high reflectivity for two or three decades!

The secondary mirror in the Skyliner 200P has a diameter of about 50mm, giving a 25 per cent central obstruction. This provides full illumination over ~ 25mm of the central region of the 46mm diameter field of view; a good compromise for all round use. Yet, Orion Optics UK also offer the amateur the opportunity to buy a smaller secondary with a diameter of 36mm, thus reducing the central obstruction to just 18 per cent, in order to optimise the instrument for planetary and double star work. Heck, one could keep both flats and inter change them as and when required!

Man and his technology!

Small modifications to the existing secondary, such as thoroughly blackening the sides of the mirror and the supporting structure would cut down on glare from bright objects. Flocking the tube with low reflection material, especially opposite the focuser, would also improve the overall contrast of the image reaching the eye.

Black paint skillfully applied to the secondary flat mirror and supporting structure would be a worthwhile project to improve overall performance.

Black paint skillfully applied to the secondary flat mirror and supporting structure would be a worthwhile project to improve overall performance.

 

 

 

 

 

 

 

 

 

 

What exciting telescopes these 8-inch Dobs are; lucis in caelo!

23:00h: With all the moving about the ‘scope has thus far endured, I decided to check collimation of the Newtonian, discovering that it was a wee bit off perfection. That’s how accurate the laser collimator is! Set it upon my kitchen table and tweaked collimation until it was spot on again and then set it out to cool.

Tuesday, February 17:

00:30h

Ambient: +1C, blustery northwesterly sleet showers coming and going all evening.

Seeing quite poor (Ant III-IV). En passant, neither the fully acclimated 17cm Maksutov or the Skyliner 200P were giving good stellar images this evening. Only the easier doubles were resolved; Gamma Leonis was pretty at 150x and Mizar & Alcor lovely at 120x, their seeing discs large and ‘boiling’ in both instruments, but sightly more so in the bigger Newtonian. I attribute the latter to its greater sensitivity to atmospheric turbulence

Jupiter looked rough even at 150x but I was still able to watch the GRS whirl across its disk in both telescopes, the slightly larger Newtonian showing it that little bit more easily throughout.

Thursday, February 19: Having discussed the tremendous value of the Skyliner 200P with my editor, I decided to embark on a project to make the aforementioned modifications to the instrument in order to maximise its potential. The project will be featured in an up-and-coming issue of Astronomy Now and, at some later stage, on this website too.

Thanks for reading my story so far.

I leave you now with a short video on Sir Isaac Newton’s original reflecting telescope, its speculum mirror and the ingenious design of the tube and mount.

Man and his technology!

Wednesday, April 1, 2015:

I got both mirrors re-coated but in the end decided on just one secondary of 44mm diameter, and not two as I considered previously. This secondary provides a very decent 22 per cent obstruction – less than my Maksutov and a good compromise between a smaller secondary and a larger one. This still provides excellent illumination even towards the edges of the field with a low-power 2-inch eyepiece. I bought a water butt that perfectly fits the mushroom knobs under the base of the lazy suzan mount and provides both a stable and more elevated platform for more comfortable, seated visual use. I have undertaken all the modifications to the tube mentioned previously.

23:15 hours.

After putting the whole thing back together this afternoon, I set the telescope outside with its caps on about an hour before my teaching finished. As luck would have it; the sky was both clear and tranquil (seeing I-II) and I trained the instrument on Jupiter. Wow! Incredible detail such as I’ve never seen in the smaller Maksutov! I watched a beautiful shadow transit of one of the Galilean satellites. The GRS was near the centre of the disk and the satellite shadow was directly north of it.

I made a sketch to record those moments.

Time: 20:40-50h UT

Seeing: Ant I-II

Object: Jove

CM II: 236 degrees

Magnification 170-190x

Jupiter as seen in an 8" f/6 Newtonian reflector o the evening of April 1, 2015.

Jupiter as seen in an 8″ f/6 Newtonian reflector on the evening of April 1, 2015. North is at the bottom.

 

 

 

 

 

 

 

 

 

 

 

 

 

By 22:00 BST, I had successfully split Theta Aurigae and the magnificent triple system, Iota Cassiopeiae.

This is my best telescope, no doubt about it, but it’s also considerably less (even with the mods) expensive than the 180mm Mak and my 5 inch refractor.

In time, it will become my most used telescope.

Aperture wins. Period!

Don’t let any  wooly thinking cloud your judgement!

And so, it only remains for me to bestow a name on my powerful speculum; eight inches of Newtonian bliss.

Only one appellation trips off the tongue: Octavius!

Octavius.

Sailing away with young Octavius.

 

 

 

 

 

 

 

 

 

 

 

 

Saturday, April 4, 2015

An Evening with Octavius & Cornelia

Time: 22:00 BST

After a beautiful bright and reasonably warm day, I set up both my 17cm Maksutov and Octavius side by side and allowed them to fully acclimate over a couple of hours with the optics capped. I watched the Moon rising in the East and brilliant Venus in early gibbous phase setting in the West. When dusk arrived, I discovered that the seeing was near perfect! Hardly a quiver on Theta Aurigae at 340x in the Maksutov. Comparing the Jovian images one more time, I got the same result; two lovely instruments capable of rendering excellent images but one clear winner; the 8″ f/6!

The images are more stable in the Maksutov, owing to its greater insensitivity to atmospheric turbulence but that said, when the images settle down in the Newtonian, it easily shows its superiority to an attentive telescopist.

I would welcome people to test this claim and report it to as many astro folk as possible.

The biggest surprise though was the efficacy of the reflector in resolving the tricky binary system Iota Leonis. At magnifications of 225x, the 8 inch speculum showed me the clearest view of its elusive secondary that I have yet seen in any telescope. It’s raw resolving power is a law unto itself!

This is very encouraging as it means that there will be nights where I can push the 8 inch on pairs that are deemed very tough for my smaller instruments.

There is something very sweet and pure about this telescope; it’s understated power and charm shine through when just a little care and attention is afforded it.

My exchange with the public.

Battle o' the Specula.

Battle o’ the Specula.

 

 

 

 

 

 

 

 

 

 

 

 

 

A Triumph for Octavius!

For the defeat of badness with goodness!

For reason over darkness.

For diligence over laziness.

For vanquishing bluff with truth!

For heart filled humility!

And the ostrasization of hubris.

A Triumph for Octavius!

Go in Peace Octavius!

 

 

 Tuesday, April 7, 2015

Continuing to learn from Octavius in good seeing. Started a blog on my adventures on CN to save some space on my site. Thank you CN!

I am eternally grateful to Cornelia for teaching me the ways of Octavius.

On vacation until next week.

Wednesday, April 15 2015

Time 20:45-55UT

Work on CN aborted owing to account suspension.

After a rather grotty few days compared with what our neighbours south of the wall have enjoyed, the clouds cleared in the late afternoon here and it stayed that way for the rest of the evening. After work, I set Octavius outside to cool for about 40 minutes from my heated office. That was enough time to get it serving up excellent images of Jupiter in very good to excellent seeing (I-II). My favourite magnifications are about 170x with the Televue BPL filter in place. Though less than 50 degrees altitude at this time, the 8 inch speculum rendered some really fine details within the planet’s vast belt system. The NEB was a heaving mess and the SEB distinctly bifurcated. When I began my observations at dusk at 20:30UT, the GRS was just coming round the eastern limb of the planet and over the next half hour I watched it grow more and more distinct as it edged its way into the disk.

I made a sketch of my impressions at 20:45-55 UT CM II 182 degrees.

Jove 15.04

It is hard to describe the image of the planet in the Newtonian. It ‘flits’ back and forth between slightly blurry and magnificently sharp over the seconds and minutes. I have learned to completely ignore the spider vein shadows superimposed on the planet’s disk. They are largely cosmetic in nature and have little or no impact on the resolution of fine detail.

I have not encountered much in the way of the ‘tube currents’ that other observers have reported. Indeed, I have had the instrument long enough now to judge that I do not need a cooling fan. The mirror is relatively small and of low mass and cools very quickly, even if taken out of a warm room. I am mindful also of many distinguished observers from yesteryear (Philips, Webb, Browning etc), who produced some very fine work over many years using nothing more than passive cooling to the night air. Fans did not exist during their lifetimes.

 Friday, April 17, 2015

Time: 21: 20h UT

Seeing: II-III, fully clear sky.

I set up my fine 5″ f/12 achromatic refractor (Tiberius) as well as Octavius to again compare the views in each telescope when I pointed them toward Jupiter. I also compared the views of Theta Aurigae in both telescopes.

Will report back; a shadow transit has now commenced on the eastern limb of the planet.

Saturday, April 18, 2015.

Time 23:25 UT

Both telescopes easily split Theta Aurigae at about 150x. The refractor view had a darker sky background and the pair more stably presented. The Newtonian showed the pair more easily but less stably. The explanation is probably complex; the smaller aperture of the refractor and its greater thermal stability were probably at play here. But if I were not measuring the system, the Newtonian would be the better choice; simply because everything is brighter and better resolved.

I enjoyed a wonderful shadow transit and recorded my impressions of the event at 22:45h CM II 192 degrees.

Jupiter as it appeared in the 8" f/6 Newtonian x 170x w/TV BPL on the evening of April 17.

Jupiter as it appeared in fair seeing in the 8″ f/6 Newtonian , 170x w/TV BPL on the evening of April 17.

Both the 5 inch glass and the Newtonian revealed the event well but the superior resolution of the Newtonian made it far more compelling. ‘Perfect’ linear features in the 5-inch come alive in the 8 inch speculum and were transformed into a sea of ‘imperfections,’ as a feast of micro-contrast details – entirely invisible in the refractor – popped in and out of view. And all the while, the image always flits in the Newtonian and I did experience a minor tube current that lasted for about ten minutes before it vanished.

A 8-inch f/6 Newtonian has not received much acclaim as a double star telescope but I wonder if this is yet another urban myth. I am very encouraged by the ability of the instrument to split some tricky double stars – I added Epsilon Lyrae (observed just after local midnight) and Izar to my tally this evening. I would like to flesh this interesting topic out further after I have performed more tests, but in the meantime I encourage you to look at Jeremy Perez’s website to see how well an 8-inch Newtonian can perform on binary star systems. I am also mindful of the work of the English amateur astronomer,Thomas Teague, who has measured many double stars with a quality 8″ f/5 Newtonian and a Celestron Astrometric Eyepiece.

Octavius….Optimus.

15:30 UT

I would now like to quantify the overall quality of the 8″ f/6 reflector in light of the modifications I have made to the instrument.

Here are some pictures of the modifications made.

Upgrading of the reflective coatings on both mirrors to 97 per cent. These should remain durable for at least 25 years, even in our rather damp climate.

Replacement of the secondary by a smaller one of semi-major diameter 44mm. Mirror edges blackened.

A new 44mm flat with edges blackened with matt black paint.

A new 44mm flat with edges blackened with matt black paint.

 

 

 

 

 

 

 

 

 

 

The interior of the tube opposite the focuser was flocked as well as the drawtube of the focuser itself.

Flocking the tube opposite the focuser is a good move.

Flocking the tube opposite the focuser is a good move.

These modifications give the instrument the contrast transfer of a 204* – 44 = 160mm unobstructed aperture – so a little better than a 6 inch refractor. Light gathering power will be significantly better than a 6 inch refractor though. ( *The diameter of the primary mirror as measured by Orion Optics UK)

The central obstruction does reduce the system Strehl in a quantifiable way (see below).

Graph showing the effect of a central obstruction on the Strehl ratio and Airy pattern.

Graph showing the effect of a central obstruction on the Strehl ratio and Airy pattern.

Taking a 22 per cent central obstruction and reading off the graph we get a Strehl of ~0.9.

All in all, I have a very  fine telescope in my possession, as experience at the eyepiece testifies.

Cost Breakdown

The Skyliner 200P: £288 delivered.

Water Butt: £20.00

Paint: £5.00

Flocking paper: £9.00 (including post and packaging)

Secondary mirror replacement with enhanced Hilux coatings ( including optical work to check surface flatness, post and packaging): £81.40

Primary mirror re-coating with Hilux (including post and packaging): £147.20

Total Cost: £550.60

Is it any wonder why I like to wax lyrical about Octavius!

20:00h UT

My sister in law came to visit yesterday and my wife and I  treated her to a view of Jupiter at sunset. At this precise time, the Great Red Spot was prominently on display and had just moved into the eastern hemisphere of the planet but the image was beautifully sharp. “Wow!” she explained, ” I have never seen the planet so well!

The superior coatings on the mirrors seem to have reduced light scattering in the image, improving the overall view.

When I ventured out later the same evening, I obtained a great and easy split of Iota Leonis at 339x. My first attempt at Delta Cygni was unsuccessful at 22:00 UT but it was rather low in the east at this time. When I tried again at 22:30 UT, the companion as well resolved at 225x.

Sunday, April 19, 2015

Yet another clear night tonight (remember you can always check my weather!) and time to explore some of the glories of the deep sky with Octavius.

I will report back on those activities later but for now I wish to share other user testimonies of the unmodified SkyWatcher Newtonian. I do not trust the judgement of those who express unbridled enthusiasm for apochromats. I believe their judgement in these matters is  ‘coloured’.

Here are 12 independent assessments of the 8 inch Dobsonian for your perusal.

In addition, I would like readers to compare and contrast the Jupiter drawings of Dr. Paul Abel (mentioned earlier) – a highly experienced planetary observer – who regularly uses the same telescope (albeit entirely unmodified!) as my own.

You can see a drawing of Jupiter he made with his 8″ f/6 in good seeing here.

Now, compare that drawing to one he made with the venerable 6″ f/15 Cooke refractor at Hampstead Observatory, London, just a few days afterwards (also in good British seeing).

 

Would you concede that the drawings reveal similar amounts of detail?

Tuesday, April 21, 2015

21: 40 UT

The Lyriads have been dandy this year! Hoping for the best of them tomorrow evening!

I have been very busy preparing my students for their science and mathematics exams, which are starting in just a few short weeks. But Octavius is so easy to set up and get working that I can put him to good use more or less immediately after I finish with them. The key is preparation; leave the telescope out with its caps on for about an hour and you’re cooking with gas.

Sunday evening presented near ideal conditions and I set the telescope to work showing me many deep sky objects. As dark skies will only remain for a few more weeks, time is against me and so I will refrain from providing that report until I have visited all the targets on my list.

Last night was interesting. At 21:10 UT, I had both the five inch refractor and the 8″ speculum out in the open air and fully acclimated. The seeing was unexpectedly grotty though (Ant IV), as I discovered while looking first through the refractor. I had to look very hard to see the GRS in the long glass; the details having been smeared out by the turbulent air. Remarkably though, while the image in the Newtonian was roiling in the bad seeing, I could much more easily pick it out on the Jovian disk. A modest aperture advantage is a boon on planets like Jupiter even in rough seeing. A good lesson learned!

Beginning at 20:10UT this very evening, I uncapped Octavius, turned him toward Jove and was delighted to see that the seeing had once again improved. The telescope was placed on its Lazy Susan mount an hour earlier and I gave Ciaran, my final student this evening, his first ever telescopic gander at a beautiful crescent moon dominating the lower western sky and Venus to its upper right. But first, I turned the telescope on Jupiter, dialled up 170x in the Baader Hyperion zoom (with TV filter attached) and focused the planet in the centre of the field. Ciaran peered in and after just a moment of eye-brain coordination shouted out, ” That’s so amazing! It looks like a spacecraft image!”

And it was! No GRS this time but plenty of palpable activity across its vast globe. The planet literally comes alive in the large aperture Newtonian.

He asked to look at Venus and I obliged. “This will look different,” I explained, as I unscrewed the filter. Choosing a power of 150x or so, I centred the planet and invited him to take a look.

” Wow!, he exclaimed, ” its dazzlingly bright! What’s that cross spread over the disk?

“Ah, that’ll be the shadow of the telescope’s spider veins on the planet,” I explained, turning the telescope to show him the secondary assembly.

” Oh I see!”, he said.

We ended by taking a quick look at the Crescent Moon and though quite low down, was wonderfully sharp and filled with astonishingly fine details (magnification about 80 diameters).

“Oh my God!” Ciaran said, ” that’s so beautiful!”

They say that what goes into a person cannot defile them, but what comes out, can. Ciaran spoke from the heart and revealed the truth about this telescope. And he did not defile himself.

Wednesday, April 22, 2015

23:00h

The spell of fine weather continues and the telescope performed flawlessly all night. Jupiter was magnificent. The Crescent moon was eye-wateringly beautiful! I was able to effortlessly push the magnification to 340x without any degradation of the image.

Collimation has held remarkably well thus far; f/6 is clearly a good place to be in this regard.

I visited a suite of double stars to assess the efficacy of the Newtonian. Eta Geminorum Iota Cassopeiae, Alula Borealis & Australis, Iota Leonis and later Izar. All of these are repeat observations – routine but important work in the true assessment of any instrument.  All were easily split with the 8 inch speculum. I was most impressed at the calm and well resolved images of Iota Leonis at powers up to 500x. Out of curiosity, I threaded a neutral density filter onto the eyepiece and studied the images of Iota Leonis at 340x. The filter cuts off quite a bit of the glare and attenuates the bleeding of light from the brighter primary. The background sky was also darkened producing images that were incredibly refractor like!

The attenuation of light was modest though, as judged by my ability to easily detect (with the same filter in place) the light from the exceedingly faint (magnitude 10.1) companion to Alula Borealis. I tried this trick because of what I learned from reading the works of  skilled observers from a by gone age – vis-a-vis on the large American refractors – and I believe it will be an exceedingly good and inexpensive way to help ferret out faint and tight companions to a legion of double stars within reach of my modern 8 inch reflecting telescope.

The air was so dry here that even though the telescope was left out for several hours, it did not dew up and even after I brought the instrument in shortly after local midnight, only the merest veneer of moisture settled on the outside of the tube; the mirrors being entirely dew free! That doesn’t happen very often round these parts.

My growing scepticism of many of those who have dismissed the Newtonian as a capable double star ‘scope impelled me to, once again, seek the knowledge of my ancestors. Though regrettably, their work has been summarily ignored by many of my contemporaries – I have ‘discovered’ for myself that truly dedicated observers achieved some mighty impressive results with instruments not too dissimilar to my own.

I speak especially of the work of the great British Victorian astronomer, Thomas William Webb (Anno Domini 1806-85), who resolved many sub arc second pairs with a Newtonian reflector – and had no reason to mislead others. Earlier this afternoon, I received a copy of a book chronicling his life and work.

Webb owned many smaller refractors in his early days – a 3.7 inch Tulley refractor, a similar sized Dollond and even a fine 5.5 inch Clark refractor – but eventually he settled on a 9.3 inch With-Berthon silver-on-glass reflector, which he used  with great enthusiam for the last 20 years of his life. It is especially noteworthy that despite having the privilege of observing through similar sized refractors on magnificent equatorial mounts (owned by fellow astronomers in England, including those of Dawes and Huggins), he expressed no desire to acquire one of his own.

In the words of  Robert A. Marriot, author of Chapter 8 of the book, The Stargazer of Hardwicke: the Life and Work of Thomas William Webb;

Having observed with these large telescopes, with which he was obviously impressed, Webb must have had at least some desire to own such an instrument himself, and yet for the last two decades of his life he was perfectly content to use his 9.3 inch With-Berthon reflector, which, although beyond his definition of a ‘common telescope,’ always served his needs ’till the dappled dawn doth rise’.

pp 141.

Believe me when I tell you that I know exactly how the Reverend Webb felt!

Oculus historiae

Oculus historiae

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Saturday, April 25, 2015

19:40h UT

Seeing III, excellent transparency, cool northerly airflow.

Octavius enjoying some late evening sunshine.

Octavius enjoying some late evening sunshine.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

I am thoroughly enjoying the views of Jupiter with Octavius but the planet is now well past the meridian when full darkness falls upon the landscape. I can locate the planet just before sunset and with the TV filter in place can still make out some very fine details. The GRS is now in full view on the eastern hemisphere and can be very clearly made out with the generous aperture. Soon, I will show my boys the wonders of the first quarter Moon.

21:00UT

Temperature 4C

The boys were blown away by the clean, crisp images delivered by the Newtonian. They had great fun zooming from 50x to 150x with the Baader zoom.

I returned to Venus and enjoyed looking at its marble white, slightly gibbous form. 150x is about as high as I’d like to go on this planet. It’s hard to imagine that a world that looks so comely from our clement vantage is the most hellish place that one can conceive of.

I find the diffraction spikes on Venus to be a source of endless fascination. Like the presence of modest levels of secondary spectrum in achromatic telescopes, they have a singular beauty all of their own.

A Cruciform Venus

A Cruciform Venus

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Sunday, April 26, 2015

Time 22:25h UT

Ambient: Seeing poor (IV), transparency excellent, temperature -2C, light north-northwesterly winds bringing in frigid polar air.

We had all four seasons in one day today. A freak Arctic blast of cold air brought hail and a light dusting of snow which quickly dissipated in the bright April sunshine.

Northerly air flows generally bring poor seeing to this valley and I could only manage 150x at the most on a handful of objects visited. Jupiter was poor this evening, the Moon reasonable at the lower powers. Caught a brief glimpse of Theta Aurigae’s faint companion though at 150x, which gave me a lift. All four components of Epsilon Lyrae also reasonably well (though still low down in the north east) resolved but the swollen seeing disks made the sight far less compelling. Ditto with Castor A & B and Gamma Leonis.

Called it an early night; glad to embrace the simple comfort of an open fire.

Thursday, April 30 2015

11:15h UT

With every passing hour, my admiration for the Newtonian grows. Myths cultivated in refractor forums have served to steer people away from them too long and my contempt for those who advocate apochromatic refractors in the larger sizes grows stronger day by day.

Disillusioned by contemporary telescopic culture, I am finding myself spending more and more time reading the literature of older, accomplished observers. Just this morning, I spent some time leafing through Fred W. Price’s book, The Planet’s Observing Handbook.  Like every other author of his generation (and many before him), he recommends – for sound, practical reasons – the Newtonian as the instrument of choice in the long term study of planets. The book is filled with beautiful drawings made with his own 8-inch reflector. There is something very pure and uncorrupted about his work that very much appeals to me.

In recent years, there has been a movement in the direction of ultra fast Newtonians, mainly to maximise aperture and portability. But not so long ago, opticians were making Newtonians with slower f ratios – in the f/7-12 range. With their very small central obstructions (CO) and amazing resolution and light gathering power, they would have beaten the pants off those pretentious large aperture Apos being offered to the unwary today.

Those who want that little bit more from a Newtonian would do well to consider models produced by smaller firms such as Mag1 Instruments, Orion Optics UK, and R.F Royce, to name but a few. Though more expensive than mass produced products, they are still far less pricey than their refractor equivalents and deliver excellent results that will serve you for a lifetime.

Personally, I am entirely sated by the performance of my 8 f/6 speculum, but I would love to see Synta or some such come out with a 8 inch f/7 or 10″ f/6 Newtonian models with enhanced coatings and a ~20% CO at a reasonable price. A big optics house like that should be able to pull this off without much alteration to its existing manufacturing ethos.

Check out this thread for encouraging signs of cultural change within the hobby.

Octavius: instrument of change.

Octavius: instrument of change.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

20:30- 21:00UT

Another very cold and clear night, 2C, bright gibbous Moon in the south, light northerly airflow. Seeing lower than average (Ant III-IV).

Conducted some more observations of Jupiter and a drawing made at dusk as it appeared at 20:45h.

CM II 271 degrees. Altitude ~45 degrees.

Giant Jove.

Giant Jove. 170 diameters w/TV BPL

 

I hope milder weather will come soon and with it the return of better seeing. Then I can begin investigating some sub-arc pairs.

Friday, May 1, 2015

Cornelia, my large Maksutov, has been put up for sale to raise funds to donate to the Nepal emergency appeal.

Saturday, May 2, 2015

Playing with numbers: Last night, the seeing improved quite a bit and I was treated to a beautiful image of Jupiter with the Newtonian at 170x despite its lower altitude. Later, I visited some of the show piece doubles in Bootes and Lyra.  The Newtonian has thus far proven to be very powerful in this regard. All in all, I’m very impressed with its efficacy; quick cool down, excellent performance on the full panoply of celestial targets and relative insensitivity (compared with larger specula I’ve owned) to the vagaries of the atmosphere.

That got me thinking about an old chestnut oft pondered upon by amateur astronomers; is there, in any objective sense, an ‘optimum’ sized telescope for the pursuit of my double star adventures? Then I re-visited knowledge garnered by my diligent forebears.

According to the work of John Sidgwick in his Amateur Astronomer’s Handbook,  the maximum useful magnifcation (M) is given by M = 28D^0.5 where D is expressed in millimetres. Setting  D= 200mm gives  M = 396x, so about 50 per inch of aperture for my 8″ speculum. This seems like a reasonable upper limit for most applications conducted by amateurs and over quite a wide range of fielded apertures.

The late professional double star astronomer, Paul Couteau, considered the minimum magnification needed to best see and measure doubles to be M~ > D, where D is again expressed in millimetres.

Since magnification M is F/f, where F is the focal length of the telescope and f is the focal length of the eyepiece we have:

F/f > D,  so F/D > f.  F/D is the focal ratio (relative aperture) of the telescope and the formula predicts that this minimal magnification will be achieved with an eyepiece of focal length approximately equal to the the f ratio of the telescope  you use; an observation born out well in my field experiences over the years with many kinds of telescopes.

But over what range of apertures does this hold true? It stands to reason that Couteau’s minimum magnification ought to be less than Sidgwick’s maximum magnification. This can be expressed mathematically as an inequation:

D < 28D^0.5

Squaring both sides yields;

D^2 < 748 D

Thus, one solution yields D < 748mm.

That is a most interesting result, as 748mm translates into an aperture of the order of 30 inches! Bigger sizes are (presumably) too perturbed by the atmosphere to be used( without modern technology).

Can it be a coincidence that virtually all double star work has been conducted with instruments of this size and smaller?

I think not!

But, we may go still further. Is there in any sense an optimum sized telescope between zero and 748mm? Interestingly, we may also express this mathematically.

Specifically, what aperture, D, provides the biggest difference between the maximum and minimum magnifications employed, that is, what is the optimum value of D for the function arbitrarily defined as f(D)= 28D^0.5 – D?

Differentiating the function with respect to D and setting the result equal to zero yields:

f'(D) = 14D^-0.5 -1 = 0

Solving for D yields  D = 14^2  = 196mm.

Thus, in this simple analysis, the optimum aperture turns out to be 8 inches!

LOL!

Bigger is better, of course, but not nearly as often!

Octavius; Optimus!

References: Argyle, R (ed.) Observing and Measuring  Visual Double Stars (2012).

Tuesday, May 5, 2015

A spell of unsettled weather has befallen us. All day long, sullen rainclouds drenched the landscape with life sustaining moisture. It was good, proper rain.

I’ve become much more curious about the potential of the Newtonian to explore hitherto uncharted territories in my observing experience. One of the posters on this thread was kind enough to share his experience with me regarding his success with the sub-arc second pairs; Eta Coronae Borealis and  Zeta Bootis, using a 8″ f/6 speculum.

Literature describing those kinds of activities conducted with Newtonian reflectors is well nigh scarce in comparison with the documented achievements of astronomers who have used the classical refractor. But I did find one interesting contemporary reference: Observing and Measuring Visual Double Stars (2nd Edition), 2012. In Chapter 11, written by Christopher Taylor, he crystallizes his thoughts on that very subject – The Newtonian Reflector in Double Star Astronomy.

Good with numbers, Taylor presents a proper (and I mean proper!) theoretical consideration of the Newtonian telescope in the pursuit of double star astronomy. Though he rightly acknowledges the superior stability of the images in long focus refractors, he nonetheless concludes that, given f/6 or slower relative apertures, “All the supposed optical defects of the reflector are removable or fictitious“, and further reminds us that, “a good 0.3m reflecting telescope is a far less expensive item than an equally good 0.3m refractor!

But there’s more. Taylor, rather admirably, backs up his conclusions with the results of his own observational experience using a ‘disembodied’ (my choice of word) old 12.5 inch f/7  Calver reflector with a 16.3 per cent central obstruction, erected in a “good spot” in his garden in rural Oxfordshire. There is no tube; the mirror is completely exposed to the night air and, perched seven or so feet above it, sits the secondary assembly. The mount, massive though it is, turns out to be an altazimuth! LOL!

The magnificent apparatus weighs in at an incredible 1500 pounds (680 kilos)!

On page 140, he describes his achievements with this mirror with which he employs a power of 825x on nights of excellent seeing. Though he does not mention the frequency with which he enjoys such nights, Taylor presents tables and sketches of drawings he made of  exceedingly close pairs like Delta Equulei and Beta Delphini (and many others); pairs that have orbital periods of just a few years or decades! Taylor describes the essence of why these investigations are so invigorating:

An unforgettable demonstration of this was provided by the 2005 periastron passage of the famous 169-year pair gamma Virgini…. In May of that year, gamma Vir swept through 0.3 arc seconds approach of the two stars with an apparent rate of revolution which briefly peaked at 2 degrees per week! This superb phenomena was closely followed by the author’s 12.5 inch right through closest approach, at which it was still found possible to make formal measures of p.a., yet it appears that sadly, few observers equally well equipped saw much of this spectacular double star event of the century.

His enthusiasm has rubbed off on me. I understand why he felt so passionate about seeing these things; for like ships passing in the night, it is only in the sub-arcsecond realm that amateurs can truly hope to enjoy  a ‘ringside seat’ on the dynamics of distant suns sailing far beyond the Solar System.

We cannot perceive what we cannot conceive.

Friday, May 8, 2015

Even though I have quite an extensive library on astronomical topics, of which I am very proud of, I came to realise that it was heavily biased towards the classical refractor. But I have become much more interested in the work of historical figures who used the power of the speculum mirror to advance the cause of astronomy. Accordingly, I have began to redress that imbalance by buying up several books – old and new – chronicling the lives of the Herschels who brought the reflecting telescope to the fore.

The Herschel Collection.

The Herschel Collection.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Saturday, May 16, 2015

I have not had much time to use Octavius of late owing to my teaching commitments. But I hope to redress that soon. I have examined quite a few deep sky objects on and off over the last month and will report back on my findings in due course. The length of true darkness at this latitude is now very short, heralding the onset of summer twilight which will persist until late July.

I have been reading some of the articles of Sky & Telescope associate editor, Gary Seronik, who is a long-time Newtonian enthusiast. In particular, I found Gary’s article on his 6 inch optimised Newtonian to be a good read. Seronik shows us how to get top quality views from a Newtonian at a fraction the cost of a refractor of the same aperture. And he derives even greater pleasure from the fact that the telescope is entirely home built.

Perhaps most importantly though,Seronik reminds us of the importance of aperture, noting at the end of that article that despite building and using a super duper 6 inch f/9 Newtonian, a 8 inch f/6  is, in his own words, “crushingly superior” on all targets.

No matter how much you mollycoddle a telescope, increasing its aperture is a better way to go.

Monday, May 18, 2015

CN account un-suspended but I will not be contributing there any more for personal reasons.

Friday, May 22, 2015

More musings on numbers: This thread has alerted me to the joy of establishing a theoretical basis for my experiences with Octavius. ‘Aperture’, you have heard, ‘wins’. Many know this to be true, as I do, within certain limits. But is there a physical basis for believing this? Why does resolving power scale inversely with aperture?

This leads us to Airy’s result for a circular aperture where  he showed that the resolving  angle, theta = 1.22 lambda/D, where lambda is the wavelength and D is the diameter of the aperture.

The derivation of the Airy formula is really quite involved but an email from a gentleman in the States (thanks Jim!) prompted me to look at a simpler approximation based on one rendition of Heisenberg’s Uncertainty Principle. Airy himself did not have knowledge of such physics, as this was only developed in the early 20th century. What follows is an elaboration of the approach of Dick Suiter, in his book, Star Testing Astronomical Telescopes.

Starting with the momentum/ position inequality.

delta p x delta y~ h where delta p is the ‘fuzziness’ in the momentum in the y direction and delta y is the fuzziness in position y. h is Planck’s constant.

Rearranging this formula we get;
Delta p/p ~ h/(p x delta y)

The momentum of the photon can be expressed as E/c and since E = hf  where f= c/lambda we get E = hc/lambda (wavelength). Delta y can be considered to be the diameter of the circular aperture, D.

So p = E/c = hc/(lambda x c) which simplifies to h/lambda

so delta p/ p ~  h/ (p x delta  y) ~ hc/fhD and since c/f = lambda the formula reduces to lambda/D.

Thus, the resolving angle, theta, or resolution of the telescope, can be expressed as
theta ~h/(p x delta y) = h x lambda/ (h x D) or just lambda/D.

It is interesting that this approximation is very close to Airy’s result of 1.22 lambda/D!

So it really is true; larger aperture resolves finer detail!
What is less well known to amateurs is that resolving power scales with wavelength, as shown. The shorter the wavelengths observed under, the finer the detail we ought to see.

Neat huh?

Octavius has eight inches of aperture; Tiberius, only five!

Wednesday, May 27, 2015

With the chemistry examinations taking place tomorrow, my academic work has come to an end for another year, so I have more time to finish this particular blog.

So, let us reason again, you and I.

I have already stated that I believe Octavius would give very similar planetary views to a 6- inch refractor and have a light gathering power at least equivalent to, or better than, a 7-inch  refractor.

One other way to establish the veracity of these claims is by comparing CCD images of a tough target like Jupiter.

In this capacity, I searched tinternet for comparison images taken with a 8″ f/6 Newtonian and a refractor that has garnered quite a bit of prestige in the amateur world; the TEC 140 (a 5.5 inch triplet refractor).

Here is the best sequence of images of mighty Jove I could find taken with the TEC 140.

Now, please compare these images with those taken with an unmodified 8″ f/5 SkyWatcher Newtonian. You can see some good ones here.

I have no reason to suspect any foul play,  as both imagers would have striven to show off the best attributes of their instruments. After all,  ’tis only human nature to do so!

Would you say that they are broadly equivalent?

I think the TEC images are a bit over processed and were probably (that’s a hunch, I can’t prove it however), captured using a more sophisticated CCD camera than that used by the owner of the Newtonian. The f/5 SkyWatcher Dob was completely unmodified though; so it will have a (larger) central obstruction and standard mirror coatings than my own telescope.

And yet it produces similar or even greater amounts of detail than the prestigious TEC!

But let’s now factor in the cost of these telescopes;

Suppose I were to order up a 8″ f/6 Dob from this retailer.

And then buy the TEC 140 (optical tube assembly only) from the same retailer.

The price differential is 20x!

Is there something I’m missing here?

Mein Gott im Himmel, ich verstehe nicht!

The ‘majesty factor’ perhaps?

A more ‘transcendent’ image maybe?

I can’t quantify either of those things, unfortunately, but I’m sceptical, as I know, having owned my speculum for a few months now and having personally tested many refractors of similar or larger size over several years, that both types of telescopes produce beautiful images of planets.

Octavius, with its 22 per cent central obstruction and light gathering power broadly equivalent to a refractor of the same size, must be a better all-round telescope than the famous TEC 140. Not just because I want it to (I do admit to disliking these telescopes for logical reasons); but because it has to!

LOL!

Octavius the Meritorius!

Sunday, May 31, 2015

A note on further experiments

The primary mirror of the 8-inch SkyWatcher is very good. Very smooth optics with no astigmatism. I have experimented with removing the mirror from the cell a few times now to explore the effects of tightening the three clips that hold the mirror in its cell. A word of caution:-

Over-tightening the mirror will induce marked pinching in the optics that can ruin high power images.

I have found that they should be tightened just enough so as to hold the mirror rigidly in place but only so tight as the clips can still wiggle a little. The difference between getting it right and over doing it is like night and day!

Is your primary over tightened?

I have not thought much more on improving the thermal properties of Octavius because I could possibly be blissfully happy with its native performance without a fan. But I have learned that in days gone by some reflector enthusiasts have lined their tubes with cork or, more recently, with polystyrene flocking.

Will I give this a go?

Maybees aye, maybees naw!

Some notes on low power eyepieces:

I’m not one to fuss about eyepieces, especially these days when even inexpensive stuff is so good. Of all the astronomical kit discussed by amateurs, it is arguably eyepiece discussions that produce the most heat and the least light. Don’t get sucked down that black hole what ever you do LoL!

Since Octavius is destined to become my most used telescope in the coming years, I have thought some more about getting the best bang-for-buck, low power ocular for Milky Way sweeps and for framing the largest deep sky objects. At f/6, the 65 degree AFOV Erfle gives good performance but my attention was piqued by a new eyepiece marketed by Explore Scientific. As part of their Maxvision range, the company offer a 40mm model with improved coatings and eye relief, an adjustable eye cup and a larger 68  degree AFOV.

The Antares 40mm Erfle and the Explore Scientific 40mm eyepiece.

The Antares 40mm Erfle  (left) and the Explore Scientific 40mm eyepiece.

 

 

 

 

 

 

 

 

 

After testing the unit for a review (you can see that in Astronomy Now magazine) I decided to buy one as it offers enough of a performance boost to justify the switch, eventhough it weighs in at nearly three times that of the Erfle (1.25 kilos LoL)! And at £117 plus shipping, it wasn’t an extravagant splurge. Now I can play with a 2.25 angular degree field with my 8-inch speculum. M31 here I come!

Testing an' that.

Testin’ an’ that.

 

 

 

 

 

 

 

 

 

 

 

 

 

Man and his improving technology!

Tuesday, June 2, 2015

As I briefly touched on previously, some amateurs have found that using a fan which blows air over the primary to be a useful tool in bringing the optics to thermal equilibrium with the outside air.  Where I live though, there are never great temperature swings at any time of the year and my months of testing suggest that it would not really be necessary.

I’m a very lucky man!

Besides, I am not overly enamoured about the prospect of having some electrical appendage  grafted onto Octavius. It just wouldn’t feel right to me.

Wednesday, June 3, 2015

I would like to give you more.

I would like to describe my deep sky experiences with Octavius over the last few months.

Thursday, June 4, 2015
Octavius is a very impressive deep sky telescope. With a good 40mm wide angle eyepiece, I can coax fields of view in excess of two angular degrees out of it. On the evening of Sunday, April 19, I caught sight of the Pleaides (M45) just above the north-western horizon, where it seemed to hover above a distant rooftop. Excitedly, I trained my 8 inch speculum and focused the stars down to tiny, crisp pinpoints. I was delighted to see that the entire cluster fitted neatly into the field of my six element Erfle! I have since replaced this unit with a significantly better Explore Scientific Maxvision ocular offering a larger field of view (~2.25 degree) with slightly better contrast and edge-of-field correction. From a dark and transparent sky, my 8-inch speculum provides lovely, contrast-rich views with only a slight drop off of light at the extreme edges of the field. This edge-of-field vignetting is entirely acceptable though.

The improved coatings on both mirrors came into play when I visited the great globular cluster, M13 in Hercules. I could push the telescope to 200x before the image became too dim. The view was spectacular though, more reminiscent of what you would get with a standard 10-inch Dob. The cluster was beautifully resolved with hundreds of stars cleanly resolved to the core. The widely reported ‘propeller’ streams curving out from its main body were very obvious with a direct gaze. When I swung the telescope over to M92, I wasn’t disappointed either; a veritable swarm of white stars at 200x, more condensed than M13 but still well resolved almost to the centre.

Spring galaxies also benefited from the improved coatings. The celebrated M81 and M82 were easy pickings for this telescope, with both ‘Island Universes’ revealing excellent structural detail at powers of 150x or so. The improvement was obvious compared to a 17cm Maksutov set up along side it.

More exciting still, I could more easily trace out the spiral arms of the Whirlpool Galaxy, M51, in the constellation of the Hunting Dogs. The difference between the views in the smaller Maksutov and the larger Dob was subtle but quite obvious. The same result was observed when I swung the telescopes down to the Sombrero Galaxy (M104) in Virgo. The greater light grasp and resolving power both came into play to deliver a noticeably superior view in the Newtonian than in the Maksutov, where it was easier to see the prominent dust lane bifurcating this classic edge-on spiral at powers of 150x or so.

Open clusters are a pure joy to observe with Octavius. The Double Cluster (C14) in Perseus was beautifully framed at 30x. I spent a good twenty minutes in the wee small hours of Monday, April 20, in sheer awe observing this spectacular communion of stars. The superior light grasp of the reflector over either my 17cm Maksutov (now gone) or 127mm refractor was painfully obvious, my eye being able to differentiate white, blue-white, creamy, orange and downright ruddy constituents at moderate powers (100x or so).

Having become intimately familiar with the appearance of the three bright Messier clusters in Auriga in my 5-inch refractor, I was simply stunned at the difference manifested in the 8 inch speculum. While they are beautiful in the 5 inch glass, the view of M36, M37 and M38 in the larger speculum are quite simply in a completely different league!

The same was true when I compared and contrasted the views of the famous planetary – the Eskimo Nebula (NGC 2392) in Gemini – using the 8-inch speculum to my smaller Maksutov and refractor telescopes. The superior light grasp and resolution of the Newtonian allowed me to push the magnification to significantly higher powers. I found 250x presented the best views, with the bright, 10th magnitude central star being clearly differentiated from not one, but two diffuse, concentric shells of luminous matter. In contrast, the smaller ‘scopes maxed out at powers at or slightly below 200x. Shell detail was also a notch down in these smaller instruments.

All in all, I am positively delighted with the deep sky views served up by my 8-inch light bucket. From my relatively dark country sky, it will provide a lifetime of wonderful sights to visit, some for the first time, but many to be returned to again and again with the passage of the seasons, like faithful old friends.

Haste ye back the dark skies of August!

Friday, June 5, 2015

Having sold off some gear that I no longer need, I raised some more funds to purchase a better finder for Octavius. Nothing fancy; a SkyWatcher 9 x 50 right angled model, which can be bought new in the UK for a very reasonable price (£59). Such an upgrade will enhance my observing experiences by reducing neck strain and should make finding objects that little bit easier.

With June now upon us, the skies never get truly dark here. At such times, I turn my attention to double stars since they are little affected by twilight. Summer can present quite excellent seeing here (as revealed in many previous blogs), especially if its settles down for any length of time. I am very excited about examining progressively tighter pairs  to see how much I can push my 8 inch speculum. Once this study is completed I shall bring my public telescope reviewing to an end.  I pray that the weather will be kind to me in the coming weeks.

Saturday, June 6, 2015

Time : 00:05h BST

Ambient: 10C, brisk westerly wind, good transparency. Seeing fair to good  (Ant II-III).

I got off to a solid start this evening. Octavius was placed outside and left to completely equalize with the night air. No dew as the wind is too strong.

Izar ( Epsilon Bootis) beautifully split at 225x. Faithful colours – yellow and blue.

Epsilon Lyrae 1 & 2 easy at all powers above 100 but best seen at 225x

Alula Australis: lovely near equal magnitude split at 225x

Delta Cygni; easy pickings at 225x

Zeta Herculis – unsuccessful, strongly elongated at 225x and 340x. Will need calmer conditions to bag this puppy.

00:30h: The bonnie triple system, Iota Cassiopeiae, beautifully resolved at 225x, despite its fairly low altitude in the northern sky.

No’ bad ken.

Telescope put away. Time tae hit the hay.

21:00h BST: Heehaw else tae report today.

Dreich weather ken.

Get it roond ye!

Get it roond ye!

 

 

 

 

 

 

 

 

 

Sunday, June 7, 2015

Time: 19:50h BST

The Lord works in mysterious ways. After a day of downright rotten weather, today has been much better and this evening promises more clear skies! I have no idea how good they will be but at least I’ll get a chance to field my best telescope once again.

In addition, it occurred to me that I have another witness to my own weather conditions, someone impartial, who lives near me, and has been a contributor to this blog. He can vouch for my blue skies.

Indeed, maybe the same gentleman can vouch for most, or even all the observing-related weather entries I have made on this blog/review since its inception at the end of January last?

Hey, how lucky am I?

Just a few hours to go before my next adventure.

Fingers crossed eh!!

A white Knight upon a dark horse.

A White Knight upon a Dark Horse.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

22:40 BST

Ambient; westerly wind has all but abated at ground level but with some isolated cloud patches moving swiftly across the sky at high altitudes. The cursed wee midgees came out earlier but now the temperature has fallen to 7C, so not likely to pose a problem going forward. Some good images of Arcturus.

Midgees eh!

23:30 BST

More cloud encroaching, seeing a notch or two down on last night (Ant III). But still managed a clean split of Izar at 170x. Seeing disks more turbulent tonight though. Ditto for Epsilon 1 & 2 Lyrae. The quartet were fairly stably held at 340x but with frequent morphing of the image in and out of focus as the stars swept through the field. Don’t see much point in continuing higher resolution targets tonight. Need to wait for better nights.

Monday, June 8, 2015

A Note on Collimation:

As anyone who uses a Newtonian regularly will tell you, alignment of the primary and secondary mirrors is absolutely critical  to gaining the best possible images. Some folk  get in a right guddle with this procedure though, while others border on being OCD, checking it two or three times per night. LOL!

As briefly touched on earlier, collimating a f/6 Newtonian is fairly straightforward and is rendered almost completely pain free using an inexpensive laser collimator (I use an inexpensive SkyWatcher unit). F/6 or slower systems can be accurately aligned  during the day but I tend to always back this up with a star test before beginning serious observations.

You can find a very good demonstration of how to quickly collimate your Newtonian here.

I would say however that it is better to do the collimating on a horizontal bench/table so as to avoid the small risk of one of the Allen keys falling down the tube and hitting that all-important primary mirror – yikes!

Looks like the weather is good again for tonight, so perhaps some better opportunities to  split some tougher pairs.

New finder should be with me tomorrow- yeehaw!

 22:00h BST

At last, a fairly warm and bright day. And the day has given way to what looks to be a clear and tranquil night.

I walked through the garden in the cool of the evening. With a song on my heart and a spring in my step, I retrieved Octavius from my office and set it out to cool.

The warmer temperatures have brought out more insects. The swallows feast on them high in the sky – a good sign that fair weather is here for a while. Nearer ground level, the bats are busy too. No wind. Only the sound of a distant cuckoo breaks the silence.

Will report back later.

23:45h BST

Ambient: 8C, twilit sky, clear and calm, seeing appears very good (Ant II).

I have just come in from examining the images of my first two targets.

Epsilon 1&2 Lyrae: Magnificent tonight! Much greater stability to the images, four tiny Airy disks surrounded by well structured diffraction rings at 340x.

Delta Cygni: Companion very easily seen and perfectly formed at 340x!

Just waiting for the sky to get that little bit darker……

Tuesday, June 9, 2015

00:20h BST

Lambda Cygni resolved tonight! Couldn’t see anything except the primary at 340x but the image was calm and very well defined. I ran to the office to get my 1.6x Barlow. This yielded a power of 544 diameters. Swung the star to the eastern edge of the field, refocused until it was at its best at the centre of the field – both members (0.9 arc seconds) well resolved! Mirror holding up really well at these very high powers!

Absolutely astonishing!

8-inch Newt owners please give this system a try, and, if successful, post it where everyone can see it!

Will talk more about it in the morning.

19:00h

My new finder arrived today. Looks cool!

A nice comfortable finder for Octavius.

A nice comfortable finder for Octavius.

I had to get up early and leave for the city this morning, so was not able to make any more observations last night. But that’s beside the point; my modified 8 inch f/6 Newtonian resolved a sub arc second pair – Lambda Cygni – and with relative ease!

Why was I astonished by this result? Well, for one thing, being used to the domination of this arena of observational astronomy by the classical refractor, it was quite a reality check to see that a Newtonian could perform so well in this regard. But there is absolutely nothing in this observation that violates any known principle of physics; I mean, according to the Dawes limit (4.56/D) my Newtonian ought to do considerably better – down to 0.57 arc seconds.

I know from previous experience with a 17cm Maksutov that in some locations I can split pairs as low as 0.7 seconds of arc. And if I can do that with a Maksutov, I can also do it with a Newtonian. Let’s just say I have faith in Octavius; not a blind faith but one that is based on reason and experience.

The fine weather is continuing but this would be a suitable place to finish.

I commend this economical telescope to you and invite you to test everything I have said about it.

It is, by some considerable margin, the best bang for buck in the entire hobby! It is a most excellent, all-round performer, an instrument that will serve up a lifetime of wonderful views and require little in the way of maintenance.

Three Cheers for Octavius: the People’s Telescope!

Update: September 27 2017

It is exceedingly rare that an individual will openly admit the true performance of a 8″ f/6 reflector compared to a ‘premium’ medium aperture apochromatic refractor. But I found one such assessment here. You will note that the gentleman in question compares the performance of his 8″ f/6 Newtonian with a TEC 140. This is what he said (I assume English isn’t his first language) about a comparison between the two instruments on Jupiter;

There is similarity with my 200mm Newton: both instruments encourage using high magnifications. For these average conditions, if my Newton allows more megnification ( about 285x) and makes detection of little contours of faint contrast easier, then there is no major difference between both scopes……..By exceptional conditions (no turbulence) I remember my 200mm going further in magnification (400x) and detection of colours and contrasts….

Then speaking of deep sky objects such as M13, the gentleman admits the 200mm Newtonian offers better resolution than the TEC 140:

M13: Splendid and perfectly contrasted. Periphery resolved but core remains ‘milky’ or granulous. Newton 200mm allows more resolution.

All in all, I feel this is an honest and realistic assessment of both instruments compared to the hyperbolic and emotionally charged statements of the somewhat blinkered (or blinded?) opinions of refractor only fanatics. This author is only too happy to test any similar sized premium refractor against his own superlative 20.4cm f/6 Newtonian.

 

 

De Fideli.

 Want to Explore More? Follow me on Facetube and Twatter