Louis D

Could you link to a source for those little arms? I can't recall ever coming across them before, so I wouldn't know what search arguments to put into google to find one. Thanks! 😁

My Vixen LV 9mm always seemed to view a bit dark, but I never noticed any distinct color tone, although I never specifically went looking for it. Despite seeming a bit dark, it didn't seem to affect dim stars right at the edge of visibility relative to other eyepieces.

Thanks for confirming that as that was my understanding as well. It would be interesting for Al or Paul to discuss what changes had to be made to account for the loss of lanthanum glass as a design option. Have they ever given a talk on the subject to your knowledge?

Yes, I got that. Perhaps something else contributed to the coffee tone. That may be why production was moved to China, to get Lanthanum glass cheaper. China has pretty much cornered the rare earths market and is reserving them for use "in house" by inflating prices to everyone else. It's one of the main reasons the Radians were discontinued because new productions runs outside of China had become cost prohibitive.

Awesome sauce! 🤩 Putting them side by side makes it easier to see the changes from one line to the next. Probably the most novel XW contribution was the introduction of the intermediate lens between the negative and positive groups in the 7mm, 10mm, and 14mm versions. Something similar was used in the Ethos and ES-100 eyepieces a few years later: I would guess it helps to realign and corral the ray bundles as they are being spread out on their journey from the negative group to the positive group. However, I don't know if it field flattens, reduces astigmatism, reduces chromatism, or a does little bit of each. Perhaps @Ruud might know.

To increase the distance between eyepieces for binoviewer usage. Not everyone has wide set eyes and/or a narrow nose bridge. Some folks decloak the already narrow TV Delites because their nose is too big to fit between them.

According to this website and Bill Paolini's eyepiece book on page 14, 1996 seems to be the agreed upon year for the XLs. The XWs came out in 2003.

Yes, but if you already have a 2" diagonal, the cost of a 2" visual back and Mak-SCT thread adapter is well under $50. I spend $300 on used sets of step-up eyepieces just to see what the fuss is about, so $50 is chump change. With the 2" visual back, I can use my 2" eyepieces like the 22mm NT4, and 17mm and 12mm ES-92s in the little Mak. Since the visual back is solidly attached to the rear plate, I'm not concerned about mechanical deformation with these heavy eyepieces, either. Also, I don't always have the AT72ED or 90mm APO attached to the other side of my DSV-2B, so it's nice to be able to get to a 1.7 degree instead of a 1 degree TFOV to better take in the surroundings of larger starfields without having to swap scopes or mount an additional scope.

The XLs have slightly brighter background skies than the XWs. Perhaps improved coatings, scatter control, and stray light control are the reason? Sharpness wise, the XLs are more consistent across their smaller fields. The XWs tend to have more chromatic aberration in the last 15% of the field and more precise eye positioning is required to avoid seeing it. That is, if you tilt your head and realign your eye with the edge, most of the chromatism goes away in the XWs. This is just a non-issue in the XLs. Both lines are equally sharp in the central 60 degrees or so. There is variation from focal length to focal length, but it seems as if Pentax was pushing the limits of their design to gain that extra 5 degrees of field at the expense of flawless correction. Field curvature wise, the two lines track pretty closely. There wasn't any real improvement there. I think the Delos made real improvements over the XWs in terms of field flatness and edge chromatism.

Yes, there were equivalent XL diagrams and specs, but I can't locate them online anywhere.

Are you sure it's natively an SCT thread? My 2" 127 Celestron Mak version's SCT thread adapter just screws off revealing the original 45.4mm Mak thread. I can't imagine Synta makes two different versions for the Celestron and SkyWatcher labels. It was a bit difficult to get it to start, but it eventually unscrewed completely off.

I wonder if Vixen discontinued the use of rare earth glass types in the SLV line to keep down expenses. I know that both the Vixen LVs and TV Radians used rare earth glasses, and both were accused of having slightly dimmer, coffee toned images as a result.

Did you miss my empirical photographic posting earlier in this thread demonstrating limited vignetting with just such a setup? It works just fine except when bright stars pass the edge of the rear baffle tube/port and create an ever larger oval reflection in the field of view. I also wouldn't recommend it for lunar or solar work, either.

In my experience, central obstructions can also make it more difficult to spot dim companions next to bright stars, as in the E and F components of the Trapezium, than in an equivalent or even smaller aperture unobstructed system. The obstruction makes the bright stars bloat so much that you just can't make out the dim companion stars no matter how good the seeing conditions are.

Agreed, the 17mm is definitely not the strongest of the three. It has enough SAEP to make it difficult to see the entire view at once when the field stop comes into view. It also has some field curvature and a bit of edge astigmatism; although I could live with those two if the exit pupil were a bit better behaved. However, it's not as bad as the SAEP in the Meade MWA 26mm I recently reviewed.

Unless you're dripping in sweat in high humidity and getting eaten alive by mosquitoes as is the case right now here in Texas. I much prefer our winter observing with pants, a light jacket, no humidity, and no bugs.

The factory 2" version of the Skywatcher 127 is quite literally the original 1.25" 127 with the optional Mak to SCT thread adapter and 2" visual back standard. Thus, the rear port and baffle is exactly the same size as the original 1.25" version. How do I know, because I've got both an older Orion 127 1.25" version and a newer Celestron 127 2" version, and they're identical at the rear ports. Celestron is owned by Synta/Skywatcher, so they're the same scope. I suppose @FLO could offer an upgrade package for the 1.25" version by adding the thread adapter and swapping the visual back for a 2" version until their importer sees fit to offer it in factory form in the UK.

That's the exact path I went down. Both ES-92s are superior to their NT4 counterparts in every way except for sheer size and bulk. Luckily, the 22mm NT4 is the best of line, so I can continue to live with it quite happily.

You could also try the 9mm Morpheus. Try as I might, I can't find much to distinguish its performance from my 10mm Delos. You'd also be giving up very little in apparent field of view.

Perhaps we could get Wikipedia writers to post a plot synopsis for @alan potts's reports/reviews like they do for movies and books for folks who want only the executive summary and not the experience? Have you asked J. K. Rowling if she could post a condensed version of her novels as well? I'm sure we'd all appreciate it since many of us don't have the spare time to read 600 page books, and having a third party write that synopsis just isn't the same as having the original writer do it. @Dippy Please do not read my reports/reviews either as they tend to be very lengthy and in depth as well; and as a Texan, I don't take well to being told I'm long winded in my story telling.

I dug around Pentax Japan with the Wayback Machine archives and located this eyepiece PDF that seems to have vector diagrams of the lenses that can be increased in size at will.

No, and I just checked the brochure tucked in with my XW 7mm, and there's no lens diagrams included on it either. 😟

I know FeatherTouch makes dual speed focuser knobs for SCTs, but I don't recall there being one for any Maks.

And these: Where the DS line indicates sagittal field curvature and the DM line indicates meridional field curvature. The origin is on axis performance and the vertical axis indicates performance trending toward the edge at the top. As the two lines diverge, it indicates increasing levels of astigmatism. The 5mm should have almost none with field curvature canceling that of most telescopes.

I composited together the max field of view in a Synta 127 Mak with a 1.25" eyepiece and with a 2" eyepiece, both while using a 2" visual back and 2" diagonal. While some may disagree with me, I think it's pretty clear that there's a lot more true field of view available in a 127 Mak with very little vignetting when using 2" eyepieces. By sampling luminosity center and at 85% to the edge in the 40mm image, it appears there's 65% of the center brightness available there which isn't bad at all visually at night.