Don Pensack

I concur on the 22mm Redline. It is far better than its price indicates. The cheapest version of it seems to be the 22mm Astromania SWA 70°, which is about USD$130. Last I checked, it was available under several different labels.

Graham, Here are some suggestions: Baader: Morpheus eyepieces--all focal lengths APM: Ultra Flat Field 30mm/24mm/18mm (also available as Celestron Ultima Edge, Meade UHD, Stellalyra UF, Tecnosky UF, Svbony UF, Sky Rover UF, Altair Astro UF, etc.) Pentax: XW 70° all Tele Vue: Plössl 25mm and longer; Delite--all; Panoptic 27mm and longer; Delos--all; Nagler--30mm, 22mm Long Perng UW/Orion LHD/Stellalyra UW 80/Founder Marvel: all ,but only IF the eyecup is removed and a shorter substitute eyecup is used Vixen: SLV--all, NPL--any of >25mm Explore Scientific: 92° 17mm/12mm; 82° 30mm (barely); 68° 40mm/34mm/28mm; 62° 40mm/32mm/26mm; 52° 40mm/30mm My personal favorites are the Morpheus eyepieces in my 102mm f/7 apo. Just really easy to use with glasses on.

Alan, The eyecup they use on the Stellalyra 20mm eats about 8mm worth of its 20mm, and the eyepiece, as-is, is not glasses-compatible, in my experience. However, if the eyecup is removed, and you added a normal flip up/fold down eyecup to the 50mm threads (a 47mm diameter rubber eyecup works), or glue some black felt to the top of the eyepiece, then it would be glasses compatible. OTOH, the 22mm Nagler is glasses-compatible right out of the box.

That depends on the f/ratio of the scope and the price of the prism. Generally, f/8 and longer scopes are OK with prisms or mirrors. Shorter than f.8, a prism tends to add lateral chromatic aberration, so a mirror is likely better. Likewise, an inexpensive prism might be better made than an inexpensive mirror type, but once you head up in price, the mirrors become the equal of prisms and may be better. One think is for sure--there are a lot more mirror diagonals to choose from. And it might be worth pointing out that AstroPhysics and Tele Vue, both makers of high-end refractors, both sell only mirror diagonals.

Only one magnification. Streaked images if longer exposures. High cost. If multiple exposures and stacking, stacking errors and the inability to screen out bad seeing. Not a panacea, but interesting.

Russ, it's OK. That is also a fine eyepiece. It's not quite as wide as the APM 24mm UFF (27.6mm field stop) or the Baader Hyperion 24mm (28mm field stop), but unless you go 2", it'll do fine. The 30mm UFF has a 36.3mm field stop, so quite a bit more "real estate", LOL.

Given where its made, it is like a spiffed-up GSO. It's probably fine. It's likely the same maker as William Optics, Astrotech, etc (GSO). I might recommend something higher end if you had an AstroPhysics 6" or something like that. But your only risk is internal collimation, which you can fix if you take your time.

Not too far from Ernest Maratovich's measurements. He got 27.6mm for the field stop, AFoV at 64°. I also measured 17mm as effective eye relief. I can't explain why he found a focal length of 24.7mm. I think he uses an instrument to measure that. (a calculated focal length makes assumptions about other measurements and can often be wrong). Since the eyepiece has some AMD due to its low RD, I'm inclined to think your focal length measurement may be close to accurate. It does make my earlier point, however, that the TF = AF/M formula is simply not an accurate one. In the absence of field stop dimensions, however, it's probably best to do a star-timing if you want to know the accurate true field size.

It could be water spots from the fluid, and/or, perhaps, the cleaner isn't strong enough. To find out, try pure acetone on one of the spots to see if it comes off. If it doesn't, it is likely to be coating damage.

It's very simple. The TF = AF/M formula is only accurate if there is no distortion in the eyepiece. Since all eyepieces have distortion, this formula overstates the True Field by 5-10%. IF the Field Stop in the eyepiece is known, this determines the true field of the eyepiece since the field stop is laid on the focal plane of the scope in the same manner a sheet of paper with a hole cut in it, laid on a map, determines how much map is seen. So the Field stop formula ignores distortion and yields an accurate true field for the eyepiece. TF = (FS/TFL) x 180/pi or True Field = (field stop/telescope focal length) x 57.2958 You can use 57.3 for the last number, which converts radians to degrees. In this case, the 24mm Hyperion's field stop is known--28.0mm, so the true field calculation follows. You'll notice that this formula also ignores eyepiece focal length, which can be in error by several tenths of a mm. The 24mm APM Ultra Flat Field is labeled 24mm, but actually measures 24.7mm, so the magnification formula will be way off. In tests, the 24mm Hyperion focal length seems accurate, but the field stop measured 28.8mm !! That means the true field will be 28.8/1250 x 57.3 = 1.32°, or 1°19' ! In truth, the Field Stop formula isn't going to be dead accurate either because we rarely know the EXACT focal length of the scope. When scopes are made, there is always a variation in mirror and lens focal lengths. Unless it has been measured on a test bench, it is likely not known exactly. There is only one easy, non-instrument, way to accurately assess true field exactly, and that is to time the passage of a star on the celestial equator across the field of the eyepiece from edge to edge. You would take 3 timings and use the longest one. Then convert it to decimal minutes (e.g. 1 minute 13 seconds = 1.217minutes) and divide by 3.99 to convert to degrees. If you want, you could then find the exact field stop diameter in your eyepiece by using the true field formula and solving for field stop: FS = (TF x TFL)/57.3 Knowing the field stop means you can figure out the true field seen in any telescope by merely plugging in the focal length of that scope. Just be aware it won't be any more accurate than the stated focal length of the scope. That error is tiny compared to the TF = AF/M formula, however.

Though because the eyepieces coma apart easily and the lenses are held in with retaining rings, they are easy to clean if necessary. I think many use them to create a different focal length for a night, and don't change them often in the dark.

Of course, you will need more eyepieces, because objects in the sky differ in size and brightness. I recommend, with that size of scope, steps of 40x magnification up to about 200x. So, since you have 50x covered, eyepieces yielding 90x, 130x, and 170x at least. That is focal lengths of 14mm, 10mm, and 7mm The Pentax XW eyepieces fit right in with the 24mm Hyperion. For less money, the 13mm Baader Hyperion plus 2 fine tuning rings can provide focal lengths of 13mm, 10.8mm, 9.2mm, and 8.1mm in one eyepiece. The 10mm Hyperion can yield 10mm, 8.4mm, 7.1mm and 6.1mm. If you don't mind threading the rings on in the dark, that makes the Hyperion eyepieces very versatile, reducing your cost for eyepieces significantly https://www.baader-planetarium.com/en/baader-hyperion-finetuning-ring-14.html Click on the graph on the left to see the details about every Hyperion with the Fine Tuning Rings added. The 24mm Hyperion isn't used with the rings, as it has no lower lenses to move farther from the upper section of the eyepiece.

A little error in the math from an earlier post. The True field of the 24mm Hyperion will be 28/1250 x 57.2958 = 1.28°, or 1°17', at 52x. That's a nice wide field, and good for a number of large objects--an excellent low power eyepiece in a 5" scope. I've always liked the C5--it has great portability and enough light grasp for thousands of deep sky objects (in dark skies).

That is nostalgia speaking. You'd be disappointed, when comparing to the Morpheus eyepieces. The 30mm UFF is a FAR better eyepiece, one of the finest eyepieces at any price. The 30mm to 17.5mm gap is not bad in your scope, either. With a 1218mm focal length, that would be 41x (30mm) and 71x (17.2mm, the actual focal length of the 17.5mm Morph.) I can't conceive of needing magnifications closer together than that. The 24mm UFF would be way too close to the 17.5mm's magnification (only 20x). The 12.5mm Morph.(actually 12.4mm) is 98x, so the 30mm>>17.2mm>>12.4mm is a pretty even spread. he next logical focal length after that is the Morpheus 9mm (really an 8.9mm). In your 8", magnifications from 40-150 will be heavily used.

It is possible to dissolve the glue and re-cement the elements, but unless you want to do it for the experience, you'd have to value your time at zero to make it worthwhile. You have a stain on the lens that will impact its usability, so you have three choices: 1) buy a new eyepiece 2) separate the lenses and clean them, then re-cement. 3) find a used version of the same eyepiece and snitch an element from it. FWIW, the fact water got in is an indication it was improperly cemented in the first place.

I'm not clear on your picture. Why isn't the diagonal simply inserted into the visual back? The visual back on the 127 looks like this: https://www.cloudynights.com/topic/624516-sw-127-mak-adapters-accessories/?p=8699550 And the external threads serve no useful purpose if a 1.25" diagonal is inserted.

IF your 1.25" eyepieces don't rest on the outer lip of the adapter, like Hyperion, Morpheus, LVW, and many other 1.25" eyepieces.

IF the scope tracks. And if the use is on planets. But if the scope is on a manual mount, a long focal length instrument combined with orthoscopic narrowfield eyepieces require the scope to be pushed every few seconds. And short focal length (10mm and shorter) Abbe Orthos require an extremely close eye position, which is uncomfortable even without glasses. It works for planets, because you can simply pull your eye back, which narrows the field you see, and you can still see the planet well. But pulling the eye back doesn't work as well for objects larger than planets (e.g. the Moon), and it means even more pushing of the scope to follow the turning of the Earth. Well-made Plössls fall into the same category--nice and sharp, with good contrast, but uncomfortable in shorter focal lengths. These are some of the reasons why wider apparent fields are popular, and why longer eye reliefs are popular (examples: Delites, SLVs, X-Cel LX, HD60, et.al.). And even at high power in a tracking scope, wider fields with good lateral correction work are more enjoyable to use on the Moon.

Don't waste your money, Louis. I could see serious lateral astigmatism in the Baader 36mm at f/10 !.

I was not referring to the threads on the back of the scope. I was referring to the "visual back", the piece that threads onto the scope, into which the diagonal inserts. On its outer end are 10mm of thread that do nothing other than to force the inserted diagonal to be 10mm farther from the back of the scope. The thumbscrew that holds the diagonal is closer to the scope, in the solid, un-threaded, portion of the visual back. Removing the 10mm of threaded section on the visual back, which was intended to be used with some obscure camera adapter, allows the diagonal to move in toward the scope, which shortens the focal length of the scope and yields a wider true field with every eyepiece. The Baader adapter to which you refer, I believe, threads directly to the scope and replaces the visual back that comes with the scope.

Are you referring to the 2" to 1.25" adapter, where the thumbscrew fits in a slot in the 2" body of the Barlow, like in this picture of a similar one:

I owned this scope for several years. It is actually a 121mm f/12.7 Maksutov with a 1540mm focal length. It's been made by Synta since around 2000-2001 and maybe before in non-USA markets, and sold under at least 10 different marks (like Orion, Celestron, SkyWatcher, etc.) It's actually 121mm in clear aperture because Maks need an oversized mirror to field the entire corrector's light, and they did not use an oversized mirror. The Sky & Telescope test many years ago confirmed that. When I had mine, I used it primarily for Moon, Planets, double stars and smaller star clusters. The maximum field with 1.25" eyepieces is 1.04°, using a Baader 24mm Hyperion eyepiece. The APM Ultra Flat Field 24mm (also available as Stellalyra and Altair Astro UFF in the UK) yields a 1.03° field. A 32mm Plössl as a low power will yield 1.00° field. The visual back that holds the diagonal has 10mm of useless thread on its outer end. If you machine this off, the focal length of the scope with a 1.25" diagonal drops to ~1510mm. This gains you so little in true field that it's hardly worth it unless you have the machine tools to do it. An eyepiece set that is usable in the scope could start with the 24mm Hyperion, but also could start with a 32mm Plössl if you want a larger exit pupil. From 32mm, the logical steps are 32mm, 22-23mm, 16mm, 11-12mm, 8mm From 24mm, the logical steps are 24mm, 17mm, 12-12.5mm, 8.5-9mm. The scopes generally don't perform great above 200x, for many reasons, which is a 7.7mm eyepiece. If you get fantastically good seeing, the scope can give decent images with 6-7mm eyepieces, but I think it's more cost-effective to use a Barlow to achieve magnifications above 190x or so. You need a finder scope, for sure, and a dewshield on the front of the scope (this can be home-made), or your observing sessions will be cut short by dewing of the corrector. You also need a nice steady mount. Due to the long focal length, look for a mount that can handle a 5" refractor. Even though the Mak is lighter and shorter, vibration in the mount is more visible due to the long focal length and large image scale.

I do a fair amount of terrestrial observing with my 4" using a conventional 90° diagonal. The image is upright, but reversed left to right. Birds, trees, buildings, etc. are still birds, trees, and buildings. I really don't see what the big deal is. I just remember to push the scope so the objective moves in the direction I want it to go. It really doesn't take any brain power. At night, it doesn't hurt in identifying craters on the Moon, or looking at celestial objects. But the Amici prisms require too much in-focus, cost a lot, weigh more, and transmit less, with poorer image quality. I really don't see the point unless it's in a finder scope attached to the main.

What scope? What magnifications result from those focal lengths? Did you collimate the scope? How are you collimating?

This depends on the scope and the orbital position of the planets, though. With my 12.5", I typically look at the crescent phases of Venus, and 100x is plenty, so I'll concur with your recommendation. For Jupiter, my lifetime best view was at 456X. Otherwise, 200x is fine most of the time--close to your recommendation. Details on the Moons require 400-500x+ Saturn needs magnification. I typically use 304X and details are readily available. My lifetime best view was at 1123X, however. That was a once-in-a lifetime experience. 200x is fine in lesser seeing, so I'll go along with your figure. Mars really needs 250-400x at opposition and even more away from opposition. My lifetime best view was at ~500x, but 250x at opposition can give a pleasant view. Surface details might take more, though. Adding a Contras Booster filter helps a lot. Uranus and Neptune really need 400-600x to see the discs well, and the fainter moons around Uranus (Triton at Neptune can be seen at 200x). At 250x, the discs are too small to see much in the way of details, though you can tell they are discs. Except for the 2 outermost planets, you recommendations are solid. Especially given Patrick's scope is an 8".