Louis D

I guess different folks have different ideas of what qualifies as small. Of topic a bit, I also never realized how big "small" fighter jets had gotten until I toured the production line of McDonnell Douglas in the 80s and realized how huge the F-15 really was while looking up at it. It's about the same size as the B-24 from WWII and can carry almost 5 times as much payload at over twice the cruising speed and range! That's crazy for a "fighter" plane. It's no wonder they created the F-15E Strike Eagle version based on these specs. Compared to a modern 24" Dob (bomber), I guess a fast 6" APO (fighter) could be considered "small". 🤔 It's all relative.

As long as you don't need to wear eyeglasses at the eyepiece, the TV Pan 27mm is a fine eyepieces. When I used my 15" f/5 Dob regularly in the past, it was my main observing eyepiece providing 71x which was just about perfect for most OCs and nebula. However, I did scratch up an eyeglass lens on the eye lens's retaining ring trying to push in to see the entire FOV once. I never did that again. 🙄 I've since replaced it in my A-team eyepiece case with the APM UFF 30mm. It now resides in the B-team case with the 12mm and 17mm NT4s that were replaced with the 12mm and 17mm ES-92s. I'll probably pass the B-team along to my grown daughter as "starter" eyepieces for her newfound interest in astronomy. 😄

The 10" and 12" Dobs you mention are quite fast at f/5, and even the mighty Leica ASPH will suffer at the edges from astigmatism. If you put your Dob on an EQ platform or get a goto version, this may not matter all that much to you. The Tele Vue Ethos line quickly became very popular among the fast Dob crowd because they are very well corrected even at low f-ratios and have a very wide field allowing for long dwell times on objects in nontracking scopes. In other words, as the object drifts from edge to edge, it remains quite sharp and observable for a longer time than in a narrower, more poorly corrected eyepiece. No zoom eyepiece comes close to this capability. I like zoom eyepieces best in binoviewers because changing out a pair of eyepieces and making sure they're correctly seated so they'll merge views is a royal pain. Also, because I use a 2x Barlow nosepiece operating at 3x to reach focus, the zooms are insulated from the fast f-ratio of the scope and perform perfectly from edge to edge.

The Altair 30mm Ultraflat is a bit above that budget (but right at it excluding VAT, which is how Americans would price compare). Being the same optically as the 30mm APM UFF, it would make an excellent low power eyepiece. It's basically a no compromise eyepiece with excellent eye relief. I don't know if it or the APM is in stock in the UK or not. There's also the newer Meade UHD and Celestron Ultima Edge versions which might be in stock.

Thanks to your Mak's f/12.7 focal ratio, you're going to max-out on usable focal lengths at around 0.6*12.7=7mm. This is assuming you can tolerate a 0.6mm exit pupil. I cannot. I have too many floaters in my observing eye. I can barely tolerate a 0.75mm exit pupil which would be a 0.75*12.7=9.5mm eyepiece in your scope. Splitting the difference, I wouldn't go below an 8mm eyepiece. The BST Starguiders have an 8mm for a good price. I typically don't go below 9mm in my 127 Mak (f/12.1).

Agreed, see my post about them here in a BV. With the right 2x (or 1.5x perhaps) Barlow ahead of the BV, it should be possible to get them to operate at about the 10mm level.

This is purported to be the Swarovski version of the Meade 7.7-23.1mm eyepiece: I guess I never heard about it having gotten into the hobby in 1997. It was apparently an early 1990s offering.

If it has 40, 50, or more dielectric coatings applied to create very specific bandpasses for one shot emission line imaging. The Radian Triad Ultra Narrowband Filter 2" comes to mind. If it was simple to duplicate, I'm sure Svbony would have come out with their version by now for $20. I'm curious how well it would work visually. The human eye is just not very responsive to far red.

From my reading of Ernest's tests coupled with user reports, it's quite sharp in the inner 70%, and then dropping off in the outer 30% at f/4 due to astigmatism and field curvature. It would be slightly better at f/5. If you keep an object centered and concentrate your attention on axis, you might never notice the aberrated edges.

Did you mean the Nirvana 16mm UWA? If so, my understanding is that it is decent at f/5, but not outstanding. Remember, these were selling here in the US under some brandings for about $65 6 or 7 years back. Don't expect 16mm Nagler T5 performance in your scope. Also, remember it only has about 10mm of usable eye relief; so you won't be able to use it with eyeglasses. If you can pick up a used one for roughly 65% of new, I'd say it's a pretty good deal.

Agreed. My Rigel QuikFinder is still going strong 22 years after buying it new with the original button cell battery. It works absolutely like new. I can't say the same for my 3 Telrads (one new, two used).

Yes, probably JOC made. Just remember, if anything goes wrong (shipping damage, faulty optics or mechanics), you have to deal with China directly, not a local dealer. Good luck with that.

Is the Orion 2x the Orion Shorty-Plus? If so, it is the same as the Celestron Ultima and Parks Gold Series which were all 3 element, Japanese made Barlows of very high quality. If it was the regular vintage Shorty, then it is of decent quality. I have a 1998 vintage Tele Vue 2x Barlow. It performs basically the same as the Shorty-Plus and Meade 140 APO 2x Barlow and slightly behind the Orion Deluxe 2x. All were made in Japan. All are exceptional performers. Only the Tele Vue is still available new, though.

Did it look like the Japanese made Meade 4000 zoom on the right in the picture below? If not, you've really piqued my curiosity. The one on the left is the newer, Chinese made version.

Maximum eye cup metal ring diameters: 12mm/17mm ES-92 = 56.5mm 30mm APM UFF = 45.0mm 22mm TV Nagler T4 = 44.0mm 17mm TV Nagler T4 = 44.0mm 12.5mm APM Hi-FW = 44.0mm 12mm TV Nagler T4 = 43.5mm 27mm TV Panoptic = 43.0mm 24mm APM UFF = 42.9mm 9mm/14mm Baader Morpheus = 42.9mm Astro-Tech AF70 (13mm/17mm/22mm) = 42.9mm So I was mistaken. My apologies. The 30mm APM UFF has an M45 thread. It is the 24mm APM UFF (and AT AF70s and Morpheus) that have M43 threads. The 12.5mm APM Hi-FW is spec'ed with an M44.5 thread. As such, the Dioptrx won't fit the 30mm APM UFF because 44mm is the maximum diameter it will clamp onto.

The 24mm APM UFF is also sold as the Altair Ultraflat, Celestron Ultima Edge, Meade 5000 UHD, and Orion Ultra Flat Field. I may have missed some European-only versions, so check around. Point is, there's a good chance someone has it in stock at a decent price. Short of a 24mm Panoptic, it's about as good as it gets at f/5, especially if long eye relief is important.

How well did the ES-62 work at f/5 for you? I have it's predecessor, the Meade 5000 Plossl 40mm. It's a five element super plossl (Zeiss Astroplan) design opened up to 60 degrees from 50 degrees. At f/6, it falls apart beyond about 50% to the edge, so I can't imagine it's actually better at f/5. Since it's a scaled design, the ES-62s should all perform the same across focal lengths. I'll admit it's very sharp in the central 50% with low distortion across the field, so the moon doesn't distort into an egg shape as it drifts across the field. Here's a comparison image showing the Meade stacked with other eyepieces at f/6 in a field flattened 72ED scope: It's serviceable for an $80 eyepiece, but not for a $180 eyepiece. I would just get the 25mm BST Starguider and call it a day: It's not perfect, but it's no worse than the Meade 5000 Plossl/ES-62, and it's a lot cheaper at £49. There's also no shame in a 32mm Plossl. Sure, it won't be perfect to the edge either, but they're only £29.

I ended up buying a couple of used Telrads at $20 a pop that had potentiometers that only switch between full on and off to replace my original one that died after 18 years. I just didn't have the time to deal with trying to make the dead one work again. Check the classifieds to see if you can locate a cheap but partially working Telrad.

How well does it work in a helical focuser? Unless it's super low resistance, it will require two hands to zoom to avoid changing focus.

Buy some rubber O-rings with an inner diameter no bigger than the outer diameter of the 1.25" insertion barrel. Measure how many millimeters you're off between the 10mm and 25mm eyepieces, divide that by the thickness of each O-ring, and slip that number of O-rings on the 10mm (which seems to focus farther out), pushing them up to the shoulder (wide part) of the eyepiece. Hopefully, there's still enough lower barrel to secure the eyepiece in the focuser. Below is an image of how I parfocalized my Tele Vue 12mm Nagler T4. I needed to add a 20mm long, 2" barrel extension to the 2" skirt to have enough barrel to insert it into the focuser. Each of the O-rings is 4mm thick times 5 rings to raise the eyepiece 20mm.

What mount do you use with your SW 100ED and BT-100ED BT, and do you move them around together?

If I get a chance, I'll use my digital caliper on it. It's quite possible since the way threads are measured, the maximum male thread width could very well exceed 43mm. Of course, if it's close and you don't need the threads, you could hone them down until it fits. 😉

I don't know that the 27mm Panoptic has enough usable eye relief for comfortable use of a Dioptrx. I've measured 14mm of usable eye relief, and that matches with my experience with it. 15mm is about the minimum recommended usable eye relief for the Dioptrx. That eyepiece is too tight on ER to use with eyeglasses. I actually scratched an eyeglass lens on the eye lens retaining ring years ago trying to push in enough to take in the entire field of view. I swapped out my 27mm Panoptic for a 30mm APM Ultra Flat Field a couple of years ago. It is flatter of field, better corrected to the edge, and has plenty of eye relief for eyeglasses. The Dioptrx might fit since it has a 43mm top thread under the eye cup. It has a 36mm field stop versus a 30mm FS for the Panoptic. That's 20% wider which is very noticeably for a mere 10% growth in exit pupil thanks to lower edge distortion. The APM is available under multiple brandings now, so it should be readily available. Another option in this price range is the 20mm APM XWA HDC. It would have about the same true field of view as the 30mm APM at a smaller exit pupil. It is available under several other brandings, so search for availability and price.

If you build it, they will buy. (or something like that)

There were also microscope zoom eyepieces from the ~1970s that could be adapted to telescope usage: