mikeDnight

I might change mine to Lenslicker, that is unless Jeremy beats me to it.

I've pondered over this problem before and discussed it at length with other observers. It seems the general opinion is that the resolution limit is based on the seperation of two stellar points. Planet's are a different thing it seems, as a linear feature too narrow to split widthwise, can still be seen with relative ease due to its resolvable length. Here's a debate for another forum!

Thanks Dave, Yes it is rapidly shrinking but still offers an observable disc. May be if you use narrow field eyepieces it will give the illusion of being bigger? It makes you wonder if the planet is only around 11 arc seconds, how wide is Dawes Fork, or even the slender Indus??

Similar view on different nights. Sinus Sabaeus, Sinus Meridiani, and Margeritifer sinus are easy to see in both observations, with Mare Acidalium in the north. The (Dawes Fork) was detected in the later observation, and hinted at in the first but obvious in the second observation was the slender wisp linking Acidalium with Margeritifer. This is known as Indus, once thought to be a canal but is in reality merely a boundary indicating a difference in terrain. The first observation was made with ice in the air and detail was a little harder to see, while the second was made with thin intermittent cloud. From January 31, 2023. A night with strong winds, and fast moving cloud in two directions. Detail was not immediately obvious and the sketch represents around 15 mins of observation to tease out what was on the sub 11 arc second disc. The observation was made using a diagonal prism so the image is north top, east west reversed. Syrtis Major is on the left of the sketch.

Looks good on you. Honest! 😁

With your scopes, it is definitely realistic to use magnification beyond what's normally accepted as the limit, especially with Mars. Ive followed Mars down to at least 4.8 arc seconds with a FC100DC and still been able to see recognisable albedo features on its surface. Have you considered the Tak TOE's as an option? They are powerful, light weight, high definition and comfortable to use, and may have an edge on on-axis sharpness over your TV eyepieces at high power.

I really like the basic Wrattan coloured filters for planetary viewing. I rarely use any filters for Jupiter, and only occasionally use them for Mars. They do help when the view is mildly turbulent and seem to steady the view a little. The most useful in my collection at W21 (orange), which enhances the darker albedo markings visible on Mars. And the W80A (blue) enhances the whites, so helps with determining more precisely the positions of clouds, mists, and polar caps. These also work well on all the planets. Also, you may find W11 to W14 (yellow) are good for Jupiter and Venus. Youll find that the larger the aperture the denser the colour needs to be to compensate for the greater ligh grasp of the telescope, so instead of a orange for Mars you may need a red. However, filters don't improve the detail across the board. They merely enhance certain features often at the cost of blocking out others. The best view will almost always be without a filter when the seeing allows. Venus in a larger aperture scope may benefit from a variable polarizing filter to reduce the glare rather than any particular coloured filter. If you are among the lucky ones who are mildly sensitive to UV, you may see the subtle cloud top detail on Venus without the need of any filter.

Hi Rich, You might try tightening all the screws and bolts in your tripod as often they can be a little loose from the factory. The tripod is often a weak point so by ensuring everything is secured properly, including any accessory tray, you'll give the mount better stability. There may still be some tremor in a 900 mm scope on an eq2 though. I like the idea of a zoom eyepiece mentioned by M40, and I believe that Skywatcher sell a nice zoom which was reviewed by John Huntley some time back, and its quite a bit cheaper than the Baader zoom. You could look on UK astro buy & Sell, or here on the SGL for sale section for second-hand eyepieces which generally work out a third cheaper than the new price.

The title of the post was refractor for visual, so presumably the op wants to know which refractor would be a good choice for visual observing. It seems that due to cost and ease of use, the humble 4" is a strong contender as a general purpose instrument. A 5" or 6" refractor would be better as far as being more capable, but cost can be the limiting factor. And may be the op doesn't want to cart a large cumbersome tube assembly outside each time he wants to observe, as although it may initially be appealing to have a big reflector to play with, the in practice experience may not be so pleasing. I know that I personally much prefered observing with a small refractor on most occasions, despite large reflectors being alongside. One reason I like a good refractor is because of the definition. Aperture isn't everything, as has been proven time and again. I've seen a beautiful detailed view of Saturn through a fine 200mm Dob on an excellent night of good seeing, made to look utterly lacklustre when compared to the view of Saturn through an 120ED alongside it. If the resolution gain of the 200mm was all that mattered, then he 200mm would surpass the 120ED showing the ultra fine divisions within the ring system, but it didn't. The difference was so obvious it was hard to comprehend, yet the smaller aperture refractor left the Dob way behind in terms of definition.

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That's brilliant! I am sorry though, it was my spell correct incorrectly correcting my incorrect spelling. But Smugness and Takahashi do seem to work well together. 😂 I meant snugness of course.

I think I'd be tempted to buy some felt and cut it to size, then trying it for smugness before gluing it in position. Even three felt pads may be all you'll need?

Schmidt originally designed his telescope to be a camera, so it's not surprising that's where it shines. DP is an imager not a visual observer, and so it's not surprising his choice of telescope is a Schmidt Cassegrain.

You have a beautiful looking scope there Craig. I think You should take another look at M42, but with a 20mm wide field eyepiece and from a dark site. You might just view your "little pea shooter" as you call it, in a completely new light. About 15 years ago i was observing with a friend from a dark site out of town. He was using a Vixen 102 F6.5 ED and I a NP101. My friend was looking at the orion nebula using a low power eyepiece of around 35mm or 40mm fl. I looked through his scope then suggested he try my 20mm Nagler. He said "No thanks, I like the low power views", but I encouraged him to try the 20mm. I wish I hadn't, because by the end of the night he'd somehow talked me into selling the 20mm Nagler to him, and cheap as he didn't have much money. Truthfully, the view of M42 in his 102ED with the 20mm Nag blew his socks off. The nebula was spectacular, and filled the field like a pearlescent green gaseous clam shell set against a much darker sky background. Not only the bright nebulosity stood out better, but the dark black nebula exploded in tiers one behind another, giving depth to the view and a very 3D impression. The wow's and colourful expletives must have gone on for 20 or 30 minutes. If you can't find a dark site, then try observing from under a blackout blanket for a while. Transparent nights will be best of course. You'll be amazed!

That would presume that every SCT I've used, none of them mine, were out of collimation, which is definitely not the case. I've been in the game long enough to recognise an out of collimation image. When compared to every other design of scope, SCT's have proved themselves time and again to be the over all worst visual instrument I've ever encountered. As I mentioned in a previous post, I've only seen one SCT, an old 1980 orange C8, in 43 years that gave a stunning view of Jupiter. As a visual lunar and planetary observer, a classical Cassegrain or Mak Cass would be a preferred choice for me. I am happy you have a good SCT though!

Excellent sketch. It's encouraging to see what a smaller aperture scope can really do. Thanks for sharing.

I dream of Texas skies Louis. In 43 years observing from the UK, I've only once seen a Schmidt Cassegrain give a good planetary image. They invariably deliver bland, barely focused planetary images, with stars presenting as blobs rather than stellar points, and soft lunar views. Mak Casse's fare way better for some reason? The 10" F6.3 Dob I had would always resolve more planetary detail than my 4" refractor, but it wasn't as enjoyable to use, and the spider diffraction would spoil the planetary views for me. The 8" was not much better at resolving planetary detail than my 4" which i found surprising, yet it was much more of a beast to handle. Plus, because the 4" is such a good scope, magnifying beyond the 200X resolution limit isn't much of a problem if the seeing is steady; its amazing how much detail is in a small planetary disc when the image scale is increased a little. However, if you know of anyone who would like to buy me a 12" Obsession I woul receiveit gladly.

I think it would pay for you to look through a few different scopes before making a final decision. I'm sure that Preston has an astro association where you can chat to fellow astronomers and observe through their scopes. You may find that a 4" ED will keep pace with an 8" reflector on the moon and planets, and an awful lot more pleasurable to use. Here's a pic of my 8" F6 Newtonian, 10" Dobsonian, and my two 4" refractors as a size comparison. The planetary resolution on the 8" was barely discernible over the 4" Takahashi. The 10" was noticeably better at resolving finer detail, but the image was less pleasing, less sharp, and smeared with spider diffraction spikes. The 10" and the 8" we're cumbersome scopes to use, and for the majority of the time I found I prefered the refractor. 8" 10" 100mm Takahashi fluorite apochromat. 101mm Genesis SDF rich field refractor. Here are a couple of sketches of Mars from the 2020 apparition, the first made using the 8" Newtonian and the second using the 100mm Takahashi. Apart from the images being mirrored, the 8" shows little gain over the 100mm refractor.

Hi Geoff, I'm talking about an apochromatic refractor such as Michael's lovely Starfield ED above. I've used many ED and Apochromatic refractors and they are in a different league to the SW achromats. I learned that the hard was back in January 2003, when my Helios 150mm F8 achromat was utterly annihilated by a Vixen 102mm fluorite apochromat. The difference was so stark that I never looked through the 150mm achromat again. A couple of years later at an Easter star party at my local astro club, an elderly man who'd looked through every other scope on the field, some very big scopes of every major design, came finally to the Vixen. He took a long look at Saturn, then asked "Why is this one so much better than all the rest"? So even a complete novice with no axe to grind could see the difference. Back then there were only Vixen, Takahashi, Astrophysics and a new kid TMB. Skywatcher ED's were just about to take the astro community by surprise.

It would certainly seem so, but it's important to remember that each scope design brings something different to the table. Much depends on what you want to observe, or what interests you. If for example you want to look at galaxies, a large Dobsonian or Newtonian will leave even the best Apochromatic refractor in the dust. But if you want to admire double stars, wide, rich star fields, festoons on Jupiter and subtle albedo features on Mars and Venus cloud tops, then a refractor may be ideal. Prices can be terrifying depending on brand or manufacturer, but Starfield 102ED and Skywatcher 120ED are very worthy contenders to consider. When it comes to high end refractors such as Astrophysics, Takahashi, TEC, Vixen, and TMB, I think only Vixen and Takahashi can be bought off the shelf.

Here are a few DSO sketches made using a 100mm refractor. I'll only post a few so as not to bore the pants off other SGLers who have suffered them countless times.

A larger aperture reflector will have greater resolution, greater light grasp, and generally cost a lot less than a good refractor of reasonable aperture. Where the refractor scores for me at least, is in its laser etched sharpness, high definition and clarity of image at the eyepiece. Refractors of 4" to 5" aperture are easy to transport to dark sites, are less effected by internal heat, hardly ever lose collimation, never need recoating, have no central obstruction and suffer from no spider diffraction. Also, they cool rapidly and even on a sub zero night can be thermally stable within 15min's if its a doublet. Another beautiful quality that a good refractor of say 4" aperture has, is its ability to magnify while retaining a sharp image. A 4" refractor is often said to magnify upto 200X, which is the telescopes resolution limit. This means that all the detail the 4" is capable of showing is contained in that 200X image, and you can't exceed that. However, because of the high definition of the image formed at the eyepiece, you can magnify that image well beyond the 200X so as to get a better image scale. A 4" refractor will show albedo markings on Mars even when the planets disc is less than 5 arc seconds in diameter, but it will likely mean you'll have to use higher powers than 200X to obtain an acceptable image scale. At the same time, a good 4" to 5" refractor will give unmatched wide field views of star fields, exhibiting stars that are so piercingly sharp they almost hurt your retina. And because of the Crystal clarity and high definition of the view, these scopes can pack a punch even on deep sky objects providing you observe from a reasonably dark sky. And one more big plus for the refractor, is that they are beautiful to look at as well as look through, so when its raining for weeks on end you'll at least have a pretty telescope to admire.

Hi Dave, Does the same thing happen if you try tracking stars?

Marginal and subtle gains can make a big difference, plus your scope is a very beautiful thing to look at when its cloudy or raining outside! ☁☁💧💧💧 I really enjoyed your drawings by the way.

I can understand your disappointment, but if you look at it as the life's passion of an amateur astronomer, you may come to view it in a different light. When I bought my three volumes during lockdown, it took me a while to appreciate it. I think it will grow on you given the chance.