Louis D

I can vouch for that. I have been able to quickly try multiple filters in this manner and home in on the best 2 or 3 for a given planetary object. Then, with two hands, I can move two filters in and out of the light cone in quick succession, and sometimes even stacked, to tease out details. If one seems to be working especially well, I'll go ahead and screw it into the eyepiece yielding the best view for that night's conditions. In this manner, I can rapidly try out multiple combinations of eyepieces and filters, wasting less precious observing time futzing about with equipment.

Now that Santa has officially gifted me this eyepiece at Christmas, I spent an hour+ with the 3-8 Svbony zoom in my 90mm f/6.7 APO last night viewing Jupiter, Luna, Mars, and the Pleiades. Here are a few impressions that stuck with me: It is usable with eyeglasses at 8mm, a bit harder at 7mm, borderline at 6mm, and pretty much unusable from 5mm down to 3mm. This runs contrary to my flashlight projection measurements showing a pretty consistent 8mm or eye relief. At the long end, I'd say it has about 15mm of usable eye relief. Zooming in, I can see the AFOV retreating into the distance (actually just narrowing in subtended angle) sort of like that "sunken place" scene in Get Out, forcing me to cram my eyeglasses harder and harder into the eyepiece. For 5mm and below, I removed my glasses, but the eye relief was still almost too tight to use comfortably. Based on that, I'd say ER drops from 15mm to 8mm as you zoom from 8mm to 3mm. It doesn't feel like a linear change, though. The ER shrinkage from 8mm to 7mm to 6mm seems as relatively small as the extension of the top of the eyepiece in that range. As the top extends more going to 5mm, 4mm, and especially 3mm, the ER decreases more noticeably. It is close to parfocal, but for critical focus on objects like Jupiter's bands, an eighth turn of the fine focus knob was needed going from 8mm to 7mm. Less was needed for the next few jumps. End to end refocusing was definitely needed no matter which end was focused first. However, on star fields like the Pleiades, the defocus was hardly noticeable. It seemed like there was a touch of field curvature (focus change) center to edge across the zoom range, but it was barely noticeable. There was a bit of light leakage through the field stop indicating it is not a physical ring defining it but rather the combination of several lens edges. Field distortion seemed low. Yes, there was a bit of rolling ball effect going on during panning, but it was pretty minor. Star fields like the Pleaides looked great across the zoom range. I'll have to try it on smaller star clusters on better nights to see if this observation holds up. There is some edge astigmatism starting around 5mm which gets progressively worse heading toward 3mm. I think there is some from 8mm to 6mm as well, but it was vanishingly small. I was seeing yellow/purple fringing at higher powers across the field on Jupiter and Luna. I don't think it was seeing or the scope, but since I didn't have time to pull out lots of eyepieces or other scopes for comparisons, I'll hold off making any more comments on my chromatic aberration impressions until I can verify them through comparative analysis. It might just be an artifact of the FPL-53 triplet or the seeing. I did remove the TSFLAT2 field flattener from the diagonal and my eyeglasses from my face, but the chromatic aberration remained. Also, the center didn't seem to sharpen up all that much with the flattener removed. It is known to impart a bit of spherical aberration there. On the whole It seems like an 8mm-4mm design stretched to 3mm. Correction is excellent from 8mm down to 6mm across the field. At 5mm, it is getting just a bit worse at the edges. Things start to degrade a bit more rapidly going to 4mm, mostly at the edges but also some in the center. Pushed to 3mm, and things seem to go south. The central area is still passable, but the edges were not that great. As such, it seems like a very good 5mm-8mm zoom as far as correction and eye relief goes. The 4mm to 3mm range seems like it's mostly there for exceptional nights and strictly on-axis use. Ironically, the view of Jupiter was best at 8mm. Zooming in didn't reveal any more band details last night. Mars showed some albedo features, but I couldn't discern much else. A washed out front was moving through causing a light breeze, so that may have contributed to less than perfect seeing conditions. The ~60° AFOV is very nice. However the jump to even 70° with another eyepiece I had at hand did feel massively wider in comparison. Zooming action was smooth with just the right amount of dampening, and click stops were easy to move between. I'd say they got the mechanical action just about right. The insertion barrel is so long that it noticeably protrudes below the 2" to 1.25" adapter of my GSO dielectric diagonal, but not long enough to strike the mirror. This might prevent it from inserting all the way into some 1.25" diagonals. I suppose I'll have to check it with my 1.25" WO diagonal that I mostly use for binoviewing. (Edit: I measured it to be about 2mm short of fully seating in the diagonal.) (Late addition I just remembered) I specifically looked for light scatter around bright objects, but I didn't see any obvious issues at any focal length. This is certainly not a perfect eyepiece, but it would be absurd to expect it to be so given the relatively affordable price. Overall, I'm happy with Santa's "gift".

Also, it's easier to nail down good field performance over a 50° AFOV than over a 70° AFOV. So, for a 70° AFOV eyepiece to do it better than a 50° AFOV eyepiece is quite an achievement.

Unless the pivot point is exactly at the exit pupil, which itself can be poorly defined due to SAEP (see 26mm Meade MWA), rotating the measurement device can make the AFOV appear larger than it appears from the exit pupil point with eyepieces that either lack a field stop or have it misplaced relative to the eyepiece focal plane. I see this with Rini eyepieces all the time. I can "look under" the edge if I back away from the exit pupil and roll my gaze over to the opposite side above the eyepiece. With flashlight projection, the projected circle has a gradient field stop instead of a sharp field stop, again making it difficult to determine the AFOV. Below is a composite showing three Rini eyepieces, none of which have a physical field stop. Note how fuzzy they get near the edge even photographically making it difficult to judge what the AFOV is: My point is, some eyepieces can defy even the best measurement efforts. I also like my method for eyepieces plagued by SAEP like the aforementioned Meade MWA 26mm. I back off the camera to where SAEP is not much of an issue and take an image and go from there to figure out the "easy to view" AFOV. I suppose it's the same point as the top of the cylinder of uncertainly for its exit pupil. If the rotating device could pivot there, it should be able to get an accurate AFOV, plus or minus the effect of a field stop defined by SAEP rather than a physical ring.

Well, my AFOV measurements via flashlight method and photographic method are below: 3.5XW : 70° and 70.2° 5.2XL : 66° and 64.8° 7XW : 70° and 70.0° 12XF : 60° and 61.1° 14XL : 64° and 64.9° 40XW-R : 70° and 69.7° What methods did you use to measure your values? Photographically, the more accurate and precise method, these are all range between 0° and 1.1° off, with 0.3° being the average including the XF and 0.16° excluding it. I'm sticking with Pentax providing bang-on values for XL and XW eyepieces to within 0.24% error using 68° for the denominator. That would make the 55° claim for the 28XL to be somewhere between 54.9° and 55.1°.

Let us know how that goes as far as viewing comfort to take in the entire FOV. I've measured the 27mm Pan to have 14mm of usable eye relief. I have to push in so hard with eyeglasses to see the entire FOV that in the past I've scratched my eyeglass lens on the exposed eye lens retaining ring. I was furious. I retired mine in favor of the 30mm APM UFF. The Pan might have a bit tighter star images on axis, but that's its only advantage over the UFF that I've found. Back when I bought the Pan in the late 90s, I was actually shopping for a long eye relief 30mm SWA eyepiece with excellent correction, so it just took about another 20 years for a viable alternative to show up.

Wow, what part of Norway did that theft occur in? I picture a mostly empty country filled with fishing villages, fjords, and snow capped mountains. Norwegian cities are typically portrayed as utopian paradises on travel shows here in the US.

As far as the BCOs, it might come down to if you need astigmatism correction for your eyesight at lower powers and thus larger exit pupils. The 18mm would be too tight for eyeglasses, but the 32mm might work, depending on eye lens recession. BTW, I couldn't find a 32mm BCO, only a 32mm Baader Classic Plossl. If that's the case, I doubt if you could extrapolate anything from the BCOs to it. I'd probably look for a pair of vintage 30mm Ultrascopics/Eudiascopics instead. They're known to be of exceptional visual quality.

Find out what they've been stealing. Generally around here, they've been smashing car windows to steal laptops, phones or guns left in cars parked outside. They don't generally bother with backyards or sheds because there's generally nothing of small and high value there unless they know it's the home of a contractor with lots of high dollar tools stored outside. Generally, though, these are in a trailer, and they'll cut the hitch lock, hook it up to their own pickup, and tow the whole thing away. They don't generally break into houses given the high gun ownership rate in Texas, and the court proven Castle Doctrine to shoot to kill to protect one's abode. I'm thinking they might steal an open case of eyepieces thinking they're camera lenses, and perhaps a cased small refractor thinking it's a professional camera lens used for sports photography. I doubt they would take the time or effort to grab an entire imaging rig setup outside just due to its ungainliness. They might steal a laptop nearby yanking it free of any attached cables and cords. Think like a criminal. They want to be in and out in under 30 seconds, and they want stuff that can be easily fenced.

Based on my measurements of my Pentax XL, XW, and XF eyepieces (6 in total), Pentax has always been dead on accurate with their quoted AFOV numbers. Thus, I have no reason to doubt their number for the 28mm XL.

I read Don's write-up of the 23mm XW and concluded that I'll soldier on with my 26mm (really 25mm) Meade MWA in my quest for an ~80° long eye relief eyepiece with good correction in the 23mm to 26mm range. If I back off a bit (maybe to 17mm eye relief) to avoid severe SAEP, I can comfortably take in 79° wearing eyeglasses with just a hint of SAEP shadows. Pushing in hard with eyeglasses (just 10mm of usable eye relief) to see all 83° results in massive SAEP making it impossible to take in the entire FOV at once. As Don said in his piece, some flawed eyepieces that make up for it in performance just grow on you over time. The Meade is surprisingly well corrected and flat of field to the edge despite its usability warts. I've never tried to judge it for EOFB or contrast. @Don PensackHow much of the new Pentax's FOV is visible when backed off to a comfortable eye relief distance for wearing eyeglasses? How much does SAEP intrude at that point?

In a 14" Celestron SCT? Given its 3910mm focal length, a 27mm eyepiece would yield 145x. Not super high power, but decently high power.

I wonder if the 28mm Pentax XL which has a 55° AFOV has more distortion to account for its wider AFOV. Has anyone ever done a shootout between these two to see if they have the same TFOV?

Don't look at me. 😁 I just picked up a used 6" f/5 GSO Newt this fall and haven't had a lot of quality time with it. I wanted a decent dual speed 2" focuser for my big glass. It definitely benefits from a coma corrector with my 70 to 92 degree AFOV eyepieces. Of course, these Ursa Major scopes target an entirely different clientele. I doubt they'll be dropping in Nagler or Ethos eyepieces anytime soon after purchase.

I got initial through-the-eyepiece images and measurements taken with the Svbony 3-8 zoom in my f/6 72ED field flattened refractor. Here are my preliminary thoughts and findings: AFOV is pretty consistently 60 degrees, give or take a degree or so. If you zoom fast enough and only pay attention to the illuminated circle, you can see it subtly changes. Usable eye relief is pretty consistently 8mm from the top of the folded down eye cup. Every clickstop focal length is within 0.1mm of the claimed focal length. That is mind boggling given how far off I've found most zooms are from their marked focal lengths. The clickstops and zoom action shouldn't cause too much of an issue while viewing and zooming. I didn't need to hold the eyepiece while zooming. The 2" GSO diagonal's 1.25" eyepiece adapter's compression ring held it tightly without allowing rotational twisting. Focus is pretty much parfocal between any two clickstops. I tweaked focus at each focal length to be certain of the best image possible, but it might not have been absolutely necessary. I didn't try racking from one end to the other to check for end-to-end parfocality. I also did not check for parfocality with other eyepieces known to focus at the shoulder. I'll try to remember to do this the next time I have it out. You can't easily read the focal length scale if you have a GSO style 2" to 1.25" adapter that partially submerges the eyepiece's upper barrel to keep 1.25" eyepieces parfocal with 2" eyepieces if they all focus at the shoulder. To be certain of which focal length I was at for each photo session, I racked the zoom collar back to 8mm and counted clicks downward from there. In the same holder, it's a bit difficult to grab the zoom collar and not the eye cup collar instead. You have to get used to where it is, right at the top of the adapter. Zooming in while viewing to the 4mm and 3mm settings can be disconcerting as the top of the eyepiece lunges upward toward your eye. I certainly was unprepared for this the first time I zoomed while viewing. There's no sign of SAEP (kidney beaning) or oddball edge artifacts at any focal length. It made taking quality AFOV images a breeze. The fieldstop is nice and sharp throughout the focal range. It is a noticeably sharp eyepiece except maybe in the last 10% of the field near the edge at the shorter focal lengths. Even then, it's relatively unobtrusive in daytime testing, and I wouldn't have noticed it without specifically looking for it in my photos. I'll have to star test when the Holidays are over, and the sky clears, to confirm field sharpness at each setting. I started to come to the realization that this eyepiece might be a great eyepiece for newbies trying to populate their high power collection. If eye relief isn't an issue, it can easily replace 3.2mm, 4mm, 4.5mm, 5mm, 6mm, 7mm, and 8mm TMB Planetary eyepieces along with 3.2mm, 5mm and 8mm Starguiders/Paradigms without giving up anything except eye relief. That makes it a bargain at its current price. As I became more accustomed to it, I really began to appreciate what an optical engineering achievement this little eyepiece really is. It took the 3-6mm Nagler Zoom as a starting point, lengthened the focal range upward to 8mm and widened the AFOV by 10 degrees, all while maintaining very good optical quality at an exceedingly affordable price point. That, and the mechanical aspects are top notch as well. It just exudes quality and attention to detail. Bear with me through the Holidays. It takes significant time to edit and composite the images for my test reports, time which is scarce right now. I just wanted to give y'all a heads up that this eyepiece appears to be the real deal, and to snag it at the current discount if you want a good self-present for Christmas.

After rescuing my Svbony package from the wrong community mailbox by catching our postman late this afternoon (holiday substitutes don't know the route), I have the Svbony 3mm-8mm in hand. It's very nicely built with a smooth zooming action despite being about 6 °C straight from the mailbox. I've never felt such a mechanically precise click-stop action. It feels like a fine piece of machinery. The upper part barely moves upward zooming to the 7mm and 6mm positions, then starts accelerating faster and faster toward 3mm position. It increases a lot in length from 5mm to 4mm to 3mm. Some quick measurements with a flashlight indicate it has about 8mm to 9mm of usable eye relief throughout the range with the eye cup folded down. I can't even come close to seeing the entire field with eyeglasses when holding it up to my eye and viewing a lamp sans telescope. Perhaps at the smallest exit pupils I'll be able to get away without eyeglasses despite having 2.5 diopters of astigmatism. The eye cup folds down very easily without wanting to flip by itself like the original Morpheus eye cups. The insertion barrel is about 36mm long. I'll try it out in my normal testing rig when I get the chance. For now, it feels way more expensive than it is. I probably won't be able to get it out under the stars for a while given our extended forecast and Christmas. After all, it has to go in my stocking for a few days. 😁

I had the alpha variant back in 2021 before I was eligible for a vaccine shot. It was not fun. I wish you a speedy recovery.

@FLO Is it possible someone has already bought one expecting it to have a parabolic mirror?

I use the optics section of a Meade 140 2x Barlow on my Arcturus BV to reach focus and boost power by about 3x. Most commonly I use 20mm Svbony UWAs and vintage/adapted 15x (16.7mm) Bausch & Lomb microscope BV eyepieces. I have also used 32mm Plossls and 23mm 62 degree Aspherics with varying success. For me, I need long eye relief so I can wear eyeglasses due to 2.5 diopters of eye astigmatism which limits my choices. I've tried larger wide angle eyepieces, but I couldn't fit my nose comfortably between the eyepieces. The key thing is that the above eyepieces work well at f/12 and above. Thus, I need the 2x Barlow to boost f/6 scopes to above f/12 (f/18 actually). BV collimation is less critical with lower power eyepieces, so getting to higher powers with a Barlow, GPC, OCA, OCS, etc. and lower power eyepieces is preferable to using a pair of high power eyepieces without one.

If it ever arrives from China, I'm going to give the Svbony UHC a try. For only $19, I figured it was worth a go. Based on Star Hunter's light pollution filter test, it appears to be about the same (with a bit less blue) as the Baader UHC-S for a fraction of the price. No filter: Baader UHC-S 2″: Svbony UHC 1.25″: Spectra:

Those are physical field stop numbers. The effective field stops as I measured them photographically are 27.5mm for the 24mm (it gets fuzzy, so a bit of a judgement call) and 36.4mm for the 30mm (nice and sharp). You could probably extrapolate the 15mm and 18mm to have approximately 17.8mm and 21.3mm diameter field stops, respectively, since the 15mm, 18mm, and 24mm all appear to be scaled versions of the same design.

No, I haven't taken mine apart. It's way too nice sharpness and contrast wise in the central part to do that to it and risk ruining it or getting dust in it. I was just going by the general consensus online that since it was referred to as a Plossl and contains 5 elements, it's based on the older 5 element "Plossls" or Pseudo-Masuyamas I mentioned. I put together the following comparison of the 40mm Meade 5000 Plossl with my 38mm Rini MPL which has 5 elements and my 42mm Rini Erfle which has 6 elements. I don't know that Paul ever disclosed the design of his MPL anywhere besides declaring it has 5 elements. It was probably his most successful effort. It is probably two doublets and singlet, with the latter possibly in the center. He did tell me that the Erfle was 3 achromats. I'm guessing 50mm binocular objectives or similar. It was not a very successful design. The Meade has a 61 degree AFOV as I measured it. The MPL has 66 degrees and the Erfle has 68 degrees. Field stop diameters are 42.7mm, 42.4mm, and 46.0mm in the same order. Measured focal lengths are 40.4mm, 37.1mm, and 40.8mm (same order). Radial edge magnification distortion is 21.2%, 20.8%, and 47% respectively. This last one makes me think the Meade and MPL share a common design philosophy since the two distortion amounts are nearly identical. Clearly, the Meade is probably the best, followed by the MPL and then the Erfle. Given that the Meade performs closer to the MPL than the Erfle, I always thought of it as a 5 element "Plossl". The Meade was a good deal for the $50 I paid for it. I definitely would not pay the $289 for the 40mm ES-62 version. The 40mm Lacerta ED is a way better deal performance and price wise.

I never tried them after a friend of mine tried them and got queasy from wearing them. He did eventually get used to them, but I don't like the idea of the constantly changing correction amount depending on where I look through them. I've been wearing bifocals for about a decade now and have gotten completely used to them after tweaking a few things about them: Get big frames to push the close distance part completely below your forward line of sight, yet leaving a large enough area to be useful for close-up work. Nothing is more annoying than having to tip your head down just to look straight ahead at a distant object. This gets really tiresome driving in a hurry. Back-off the near focus distance from 8 to 12 inches to about 20 to 24 inches. Now I can clearly see my car's dashboard, read printed material on a tabletop, and read store shelves from a normal stand-off distance. Luckily, I have 20-15 corrected vision, so I can read a bit further out than most folks. Also, stairs are not completely blurry with the greater focus distance which freaked me out the first time I wore bifocals with normal reading distance (8-12 inches) correction. For astronomy use, I wear single vision distance-only glasses. I can't stand seeing the bifocal line of my daily wearers in my ultrawide field eyepieces. The pair is only used for astronomy, so it doesn't accumulate microscratches from cleanings and daily abuse. I got them in the lowest index plastic lens available to reduce chromatic aberrations with off-axis rays. I bought them from an online retailer for a very reasonable amount out of pocket. So far, I have no complaints about them. I will admit I am lucky in that my uncorrected, yet fixed, focus distance is about 12 inches, so I can just look under my distance only glasses to read the large, blocky characters on my DSC screen. I'm just dealing with astigmatism blurring at that point, which I can squint out in large part. That would be nice, but they'd be heavy (glass). I wore glass eyeglasses back in the early 80s, and they were always slipping down my nose. I will admit to taking my uncoated distance-only glasses off sometimes to see if reflections are coming from my cornea, eyeglasses, or eyepiece. Often, it is the eyeglasses, and I have to cup my hands to block the external light source. At a truly dark site, I would imagine this to be far less common. Yes, there is the issue of transmission; but again, you could flip your glasses off to see if there's a brightening in the field due to a DSO not visible with eyeglasses on.

Lucky you. Our USPS system is a joke. The regular employees are pretty good once they've been on a route a few years, but their substitutes are complete morons. Mail is continually being misdelivered because of turnover and substitutes not knowing their routes. There are no repercussions for poor job performance because there's no way to complain to the local post office. All complaints go to a centralized call center. Package delivery is very slow and expensive. Tracking and delivery confirmation is extra. When your group post office boxes in your neighborhood are broken into with crowbars to steal mail rendering them unusable, they pass the buck on replacing them saying they have to be paid for by the subdivision. When the sub tries to replace them, they're told by the USPS that only they can replace them once they've ordered the replacement and its been paid for by, you guessed it, the subdivision. USPS owns the boxes, but we pay for them. Where's the logic in that???? On top of all that, they raise rates while extending delivery times to much longer than couriers for similar prices. Couriers by contrast (UPS, FedEx, and increasingly Amazon) are in a state of competition and know their business can go elsewhere, so they tend to have on time deliveries, tracking and delivery confirmation are included with every package, and they rarely misdeliver packages, at least in our area. It is true they do have to leave packages on your doorstep leaving them vulnerable to porch pirates, but many drivers will ring your doorbell to alert you. Lately, USPS has been leaving parcels at our doorsteps once their parcel lockers are filled for the subdivision.

Look to camera lenses to see what the future may hold for eyepiece design. They use many different sorts of dispersion glass types and hybrid glass/resin aspherics. Perhaps they will trickle down to astro gear.