Louis D

There's no CLS filter in the Svbony 7 filter set.  There's a CPL, or circular polarizer.  Is that what you meant?

It doesn't matter what order you stack them in.

The Moon filter is actually a Moon & Skyglow (M&SG) filter.  It's a generic neodymium filter.  When combined with a light yellow filter such as a #8, you will get an approximation of the Baader Contrast Booster.  The #12 in the set will cut out practically all blue light, while the #8 will cut mostly violet let, leaving most blue light.

If you have bought a separate CLS filter, it is basically a wider band-pass version of a UHC filter to combat light pollution and to slightly enhance the visibility of nebula.  I'm not aware of any useful color filter combinations with the CLS filter.

Interesting.  Two different house brands, one underlying manufacturer.  Sort of like how car makers assign different brands to different market segments.

That's the more basic GSO 8" f/6 Dobsonian without all the Deluxe version's upgrades like the dual speed focuser, RACI, and movable/adjustable altitude tensioner.  I agree that the focuser alone makes it much more desirable than the basic Synta/Skywatcher 8" f/6 Dob.  I'm glad FLO has decided to add it to their lineup.

Here it is under the GSO  brand name.

The older Meade products were made in the US.

Just take the diagonal to a local hardware store or big box home improvement center and head for the fasteners aisle.  As Peter said above, look for cap head screws in M3 or M4 size and see if they thread cleanly into the empty hole.  Ask an associate for help if you're having trouble finding them as they may be in a specialty fasteners area.

With all the recent hype around the APM Super Zoom this year, I was all prepared to get in line and order one for Santa to deliver this Christmas. However, new stock didn’t show up at retailers in time, so that plan went out the window. Thankfully, another exciting new zoom debuted just before the Holidays at a much more reasonable price. Once prices dropped slightly for Christmas sales, I went ahead and ordered one direct from the Svbony website. It arrived direct from China in 2 ½ weeks. It came packed in a nice black box with sturdy, closed cell foam cut/molded to fit the eyepiece. The eyepiece itself comes in a simple plastic baggie with a microfiber cleaning cloth. There are no printed inserts included in the box.

The eyepiece box's exterior and interior are shown in the following image:

Exterior

The eyepiece itself is nice and sturdy, but lighter than its bulk would belie at 171 grams or 6.0 ounces by my scale. That makes it just slightly lighter than the 5mm AstroTech Paradigm (BST Starguider) at 6.8 ounces and just barely heavier than the 8mm version at 5.9 ounces.

The checkered grip ring is nice and broad despite the diminutive overall size of the eyepiece. It makes zooming the eyepiece easy to do. In use, I found that the focal length scale below the grip ring is difficult to read 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.

The top lens cap stays on securely enough, but not nearly as snugly as with other eyepieces’ top caps. The bottom lens cap is very rubbery and fairly loose. I would imagine it could easily get lost in the field, so I make sure to remove it and leave it in my eyepiece case to avoid losing it. This cap is rather unique in having a ribbed ring around the edge closest to the closed end. I would imagine it’s there to give users a better grip to remove it. However, this presupposes that it fits tightly, which it doesn’t.

The fairly short eye cup flips up and down easily but stays up when pressed around an eye socket. The flipped up eyecup stands about 6.5mm above the flat top of the eyepiece.

The following image shows the eyepiece with caps, without caps with the eyecup flipped up and flipped down, and with the eyecup fully removed:

The zooming action is quite smooth with positive detents at each click stop. I had no issue moving between focal lengths. The action felt quite refined. Overall, I found the eyepiece quite well made with obvious signs of precision milling inside and out.

The following image shows the eyepiece at each of the 6 zoom settings (each setting can be seen above the red dot):

The field lens is quite far from the bottom end at the all settings. What appears to be a light baffle ring moves progressively closer to the bottom end when zooming from 8mm to 3mm. I don’t believe it to be the field stop because the eyepiece barely needs refocused during zooming, yet this rings moves many millimeters. The eye lens moves dramatically upward a full 20mm while zooming from the 8mm to 3mm settings.

The following image shows the moving light baffle positions at 8mm and 3mm:

The safety undercut on the chromed insertion barrel is fairly shallow with a tapered bottom edge. No hang-up issues with focuser compression rings were noted over multiple nights with multiple 2” to 1.25” adapters. The insertion barrel is just over 36mm long and may not fully seat in many 1.25” diagonals. It remained about 2mm above the top of my WO dielectric diagonal fully seated. There is the possibility of it hitting the mirror or prism of a 2” diagonal when used with a 2” to 1.25” adapter; although I had no such issues with my 2” GSO dielectric diagonal.

The eye lens is mounted basically flush with the flat top of the eyepiece with the eyecup removed. This lens is a mere 13mm in diameter, vastly limiting potential usable eye relief. The flipped down eyecup uses up less than 1mm of usable eye relief, which is excellent. The top of the eyepiece is just over 38mm in diameter with the eyecup removed. As such, I believe it is a bit small for attaching a Tele Vue Dioptrx. According to Svbony, the top is M28.5x0.6 threaded which sounds about right. The top of the eyepiece does not rotate when zooming, so using a Dioptrx with it is an option if an attachment method can be created. There is a nice wide notch below the lip that the eyecup snaps around, so it may be possible to insert O-rings or elastic hair bands in this gap to build it up to a Dioptrx compatible diameter.

Stray Light Control

The multicoatings appear entirely greenish. There are many ridges between the moving light baffle and the field lens, ostensibly to block stray light. Lens and interior blackening and baffling appears to be good as no obvious reflections were seen with the flashlight test, but it is not quite at the level of premium fixed focal length eyepieces.

Eye Relief

Svbony claims 10mm of eye relief. I measured 8mm of usable eye relief (ER) with the eyecup flipped down. This was measured from the eyecup rubber to where the exit pupil converges to the tightest circle via light projection at all zoom settings. I have read of others online measuring it to have 10mm of eye relief at 8mm, decreasing to just under 7mm at 3mm with the eyecup removed. This seems to actually be closer to reality based on my experience using the eyepiece in a telescope, but I was unable to measure an obvious decrease using my methodology to verify this.

Weirdly enough, that 8mm to 10mm of eye relief was easily sufficient to see the entire field with eyeglasses at the 8mm setting. I didn’t need push in that hard with my eyeglasses to achieve this. I can’t readily explain this since the 13mm eye lens and measured apparent field of view (AFOV, discussed later) should yield just under 12mm of eye relief. It felt more like 14mm of eye relief.

However, the usable, perceived eye relief decreases with the zoom focal length setting. At 7mm it decreases just a bit (maybe 1mm), requiring a slightly greater push against my eyeglasses. At 6mm, even more (another millimeter perhaps). By 5mm, it is becoming impossible to push in enough to see the entire AFOV. By 4mm and 3mm, eyeglasses must be removed. Even then, my long eyelashes are pressed into the flat top of the eyepiece to see the entire AFOV. Thus, I have to pull back to blink to avoid smearing the eye lens with eyelash oil. It feels even tighter than the 7mm of eye relief mentioned above. I can’t really explain why the perceived eye relief mismatches so much with the measure eye relief.

The eyecup height is just about right for use without eyeglasses at 8mm, but is increasingly too tall at decreasing focal length settings. In fact, by 5mm, it really needs to be flipped down. Unfortunately, there's no intermediate setting between all the way up and all the way down. A mechanism to withdraw the eyecup downward as the eyepiece is zoomed toward the shorter focal length end would be ideal.

It's a good thing the top of the eyepiece doesn't rotate, or the rubber eyecup would tug at the skin surrounding the eye while zooming due to the tight eye relief. This would necessitate leaving it down at all focal length settings if it did.

The video below attempts to show the effect of decreasing eye relief in this eyepiece. I zoomed the eyepiece from 8mm to 3mm in 1mm increments and then back again to 8mm with the back of the cellphone in its case resting on the flipped up eyecup. Clearly, the AFOV visible from a fixed position above the eye lens drops off dramatically as the eyepiece is zoomed, indicating dramatically decreasing eye relief. Since the eyecup top is 6.5mm above the top of the eyepiece, and the entrance pupil of the camera is probably 3mm inside the camera lens, 9mm to 10mm sounds about right for eye relief from the flat top at the 8mm zoom setting. I didn’t try to measure the separation at other zoom settings to image the entire AFOV, but I recall it getting quite small by 3mm. I may try to measure this separation someday to get a more concrete eye relief measurement, or at least it's decrease from one end to the other. Please disregard the loud sound of the eyepiece in the video. The camera's microphone was quite close to the eyepiece. In practice, about all you hear when zooming is the clicking of each setting's detent.

SAEP

I have not noticed any spherical aberration of the exit pupil (SAEP) or kidney beaning either photographically or when observing bright objects such as the moon at any zoom setting. This is a laudable achievement.

CAEP

I could not detect any chromatic aberration of the exit pupil (CAEP) which leads to the "ring of fire" as seen in the TV Nagler T5 31mm and ES-82 30mm eyepieces. This is fairly uncommon in eyepieces of this focal length range and AFOV size anyway, but I thought I should mention lack of it to be complete.

AFOVs

Using both the flashlight projection method with the eyepiece mounted in a telescope and my photographic method, I measured a pretty consistent 58° to 61° AFOV across the focal length range. The only easy way to see the variation in AFOV is to rapidly zoom from end to end and observe the field stop in peripheral vision. Svbony only claims 56° for its AFOV which is unusual in this day of exaggerated AFOV claims. A zoom having a constant AFOV of around 60° in this eyepiece's current price range is a fantastic accomplishment.

The field of view measurements, along with several others described in the next section, are listed in the table below.

Field Stop Diameters and Focal Lengths

I photographically measured the effective field stop (FS) diameters and central and edge focal lengths at each zoom setting. They are listed in the above table. All but the 3mm setting agree well with the marked focal lengths. This is an amazing showing by such an affordable zoom eyepiece. Radial edge magnification distortion is a bit on the high side for a 60° class eyepiece.  This is visible as stretching of the distance between ruler marks toward the edge in the comparison AFOV images at the end this report.

Under the Stars

Enough about the eyepiece's specifications, how does it view the night sky in a telescope? I spent several nights using this zoom in my 8" f/6 Dobsonian without my GSO coma corrector to eliminate seeing CC induced spherical aberration at high powers and in my 90mm TS-Optics Photoline f/6.6 FPL53 Triplet APO with a properly spaced TSFLAT2 flattener. I need to spend more time with it to refine my impressions of it, but time during the Holidays has been limited due to family obligations. I will simply include the following previously posted recollections for now and update later with more recent observations as I get more time with it:

• 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.
• Star fields like the Pleaides looked great across the zoom range.
• Zooming in to the 4mm and 3mm settings while viewing 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. My other zooms don't change their physical length while zooming. While my Speers-Waler 5-8mm grows dramatically in length when changing focal lengths, I don't consider it a zoom, so it doesn't count when discussing true zooms. Instead, I consider it a varifocal since there is no effort to maintain parfocality in its design.
• The fieldstop is nice and sharp throughout the focal range.
• 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.
• 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 use, and I wouldn't have noticed it without specifically looking for it in my photos and during star testing.
• It seemed like there was a touch of field curvature (focus change) center to edge across the zoom range, but it was barely noticeable.
• Field distortion seemed low. Yes, there was a bit of rolling ball effect going on during panning, but it was pretty minor.
• I specifically looked for light scatter around bright objects, but I didn't see any obvious issues at any focal length.
• There is minor yellow fringing at the 3mm and 4mm settings. I have yet to compare my 3.5mm Pentax XW to the zoom at these settings to see if the fringing persists. I do see similar fringing in my 2.5mm TMB Planetary clone, so it might exist independently of the eyepiece.

The following notes were made in comparison to my 24 year old 5-8mm Speers-Waler varifocal eyepiece in my Dob without a coma corrector:

• Both were showing subtle lunar mara contrast details quite well no matter where I put them in either eyepiece's AFOV.
• Both fields appeared flat of focus center to edge to my presbyopic eyes.
• 5mm seemed to be the limit of usable magnification to my eyes most nights. Any higher, and my floaters got in the way, and no finer detail was revealed in the Svbony despite the higher power and greater image scale. Again, 8mm in both seemed best as far as contrast and ease of seeing fine details. Those without floaters or older eye issues might have a different experience.
• The lack of a CC didn't seem to hurt axial details moved to the edge all that much with the moon. What was more important was slanting my view with or without eyeglasses by tilting my whole head and pulling back to get a straight on view of the edge rays. This minimized chromatic aberrations.
• The S-W's 78° AFOV and 7-11mm of usable measured eye relief felt way more comfortable with and without glasses than the Svbony's 60° AFOV and 7-10mm of measured usable eye relief. There's more to ER than what the measurements say with zooms/varifocals.
• I could see the Svbony's AFOV receding away as I zoomed in. The S-W didn't seem to do this all that much. This made the Svbony's AFOV feel much narrower at higher powers than it really was.
• With my 2.5 diopters of astigmatism, the views at 6mm to 8mm were subtly sharper with glasses than without despite the small exit pupils in the f/6 scope.
• The lack of parfocality of the S-W was far outweighed by the huge AFOV and slightly longer eye relief. Much more of the moon, if not all of it at lower powers, would fit in the S-W's AFOV giving a much more satisfying view.
• The Dob didn't care how huge and long the S-W was compared to the Svbony as far as balance. This might not be the case with a small alt-az mounted refractor, Mak, SCT, or Newt.
• The Svbony handily wins out for use in a travel kit by being considerably smaller, lighter, and easier to replace should it be lost or stolen.

The following image shows the size difference between the Svbony 3-8mm zoom and the Speers-Waler 5-8mm varifocal at each eyepiece’s 8mm and 5mm settings:

Obviously, the S-W is huge in comparison to the relatively diminutive Svbony.  It’s also clear that the Svbony gets only a little bit longer at 5mm while the S-W gets massively longer at 5mm. That, and the S-W eye lens diameter at 25mm is nearly twice as wide as the Svbony’s. However, due to the S-W’s much wider AFOV (78°), usable eye relief ranges from 7mm at the 5mm setting to 11mm at 8mm setting, so still very tight with eyeglasses. This is the major reason I rarely use it, not because of its massive size or lack of parfocality.

Conclusion

I have come to the realization that this eyepiece might be a great eyepiece for newbies trying to populate their high power collection as its price decreases from its initial offering price. 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 appears to have taken 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.

Comparison Images

The image below shows the zoom’s AFOV at each of the 6 zoom click-stop settings, all at the same scale as originally taken without resizing.

Clearly, AFOV doesn't change much, just image scale.

The following images show the zoom at each click-stop setting in comparison to my other eyepieces of similar focal lengths.

All AFOV images were taken through an Astro Tech 72ED telescope with a properly spaced TSFLAT2 field flattener and then composited together in Photoshop. The objective to target distance was approximately 35 feet for all images. All sub-images were taken with a Samsung Galaxy S7 phone camera except for the “Full View” ones which were taken with the superwide angle LG G6 phone camera and then scaled up to match the central image scale of the S7 images, so the entire field of view can be compared for eyepieces exceeding the approximately 76° angle of view limit of the S7 (corner to corner).

The edge images were also taken with the S7 camera, but pointed straight at the edge to best capture the true edge sharpness that would be experienced by looking straight at the edge with the eye.

Sounds like a plan.  It just might be a pain juggling two pairs of eyeglasses.  I'm lucky to have fixed focus at 8 to 12 inches, so I just look under my distance-only observing glasses to look at things up-close.  Surprisingly, my 2.0+ diopters of astigmatism isn't all that much of an issue at that distance.

And if your budget won't stretch to Baader prices, see my recent post below:

You can pick up cheap M&SG filters on ebay UK for under £5 shipped direct from China.  Same goes for cheap yellow filters.  For under £10 you can get an idea of what the Baader Contrast Booster can do when the two are stacked together.

Notice that in all cases, it was a deliberate attack on low altitude aircraft with active tracking by the perpetrator.  Pretty much none of these conditions apply to astro laser usage.

31 minutes ago, jjohnson3803 said:

Way too much air traffic near / over me to get a laser.  The Federales take an extremely dim view of lighting up cockpits, even by accident.  YMMV.

Luckily for me, they fly into the local airport following a north to south route due east of me, which is completely obstructed by trees.  Thus, my laser would only cross paths with a few random "fly-over" planes at high altitude where the laser angle would be too far below horizontal and too diffuse to have much if any effect on a cockpit.

2 hours ago, AstroMuni said:

My wife is not interested in astronomy but she does keep tabs on the credit card statement

Luckily, my wife doesn't complain much as long as my purchases stay below $500 apiece.  I keep encouraging her to spend more money on her hobbies, but they tend to be much lower in cost than mine (cross-stitch and other crafting hobbies).

2 hours ago, AstroMuni said:

I have 2 daughters and each one has a different level of interest in astronomy. One is appreciative of what I am doing but takes no part and the other is both appreciative and does take part sometimes

My older daughter asked for an astro kit for Christmas 2018 or 2019, just before the pandemic, when she and her future husband were camping a lot.  I put one together centered on a 127 Mak and DSV-1 mount I had upgraded from a couple of years earlier.  As a youngster, she was the only one of my kids even remotely interested in astronomy.

My other daughter's long term boyfriend (and probably future husband) might be the next one to get the astro bug based on an impromptu star party I did with the gathered family on Christmas Night 2021 (it was room temp, clear, and dead calm outdoors).  He was genuinely interested in what he was seeing through the eyepiece.

5 hours ago, PeterW said:

I make an LED change between orange and green with the help of liquid nitrogen

Cool!  I've never heard of that before.

Santa officially brought me a Svbony 3-8mm Zoom, 2.5mm Planetary clone, and a Svbony 1.25" UHC filter.

23 minutes ago, Mandy D said:

Ahh, so not a simple laser, then! Essentially, you have two sources of laser light; one at 1064 nm and the other, which you want, at 532 nm. Thank you for the clarification. I was unaware that commercially available lasers operated in that mode.

Mostly just the 532nm green ones.  Beautiful green color, but nasty IR emissions which can easily exceed the 1mW or 5mW 532nm rating by 10x from what I've read due to low conversion efficiency.

FYI, huge price drop on ebay for these.  $98+tax with free shipping from China on ebay US, and £102.00 shipped from China on ebay UK.

2 hours ago, Pompey Monkey said:

From the Ebay blurb:

"Power less than 1MW"

I should hope so!!! ☠️

That's definitely a case of saying it's so doesn't make it so.  They're just covering themselves legally.  I can assure you they're blinding bright indoors.  Looking at the laser spot's reflection on a nearby wall (to check battery and switch function) will leave you with spots in your eyes for a while, so definitely not recommended if you want to critically observe in the near term.

1 hour ago, spacedobsonian said:

You know, people look at the Jupiter or the Andromeda galaxy and say "Is that it?"

Kind of reminds me of how underwhelmed I was when I finally saw Mt. Rushmore for myself.  I kind of expected it to be bigger and grander, but the heads are only 60 feet tall seen from 1000 feet away.  In contrast, I was overwhelmed by the Iwo Jima monument when I finally saw it up close for myself.  The figures are about 30 feet tall seen from about 35 feet away.  I guess I need to get within 70 feet of Mt. Rushmore to get the best effect. 😄

Try combining a cheap Moon & Skyglow (Neodymium) filter with a #8 or #12 yellow filter (depending on how much violet and blue you want to cut) to create a poor man's Contrast Booster.  You might have 10% to 20% less transmittance, but that hardly matters on Jupiter or Mars at opposition.

Here's a solar spectrum comparison I worked up to show the effects:

Compare to the official Baader spectra for several of their filters:

At f/8 and above, a spherical primary could be considered acceptable for non-planetary observing.  No amount of collimation will improve an f/4 spherical all that much.

In my own 72->90 journey, I went from an FPL-51 f/6 doublet to an FPL-53 f/6.7 triplet and have had no regrets.  That, and the mechanics of the 90mm were much better.  The 2.5" R&P focuser and camera angle adjuster make for a much better experience.  False color went from barely noticeable to nonexistent.  You're right though, even with the FPL-53 triplet, out of focus stars show red/green on either side of best focus.  The 90mm is quite a bit heavier than the 72mm as well; but it's nothing my DSV-2B mount can't handle.

If you've already got a 72mm FPL-53 doublet, you're going to need to jump up quite a bit in aperture to see a significant improvement in resolution performance.  Something like a 125mm FPL-53 doublet or even triplet might do the trick.  Of course, you'll probably need a much beefier mount.

Along these lines, I bought a 6" f/5 GSO Newtonian to see how it performs.  So far, the jury is out.  I think I much prefer my 8" Dob in every respect.  Aside from astrophotography, I'm not sure what the advantage is to a Newt on an alt-az mount.  Sure it's smaller to store, but not all that much, especially when you figure in the mount head and tripod.  That, and it has a massive secondary to favor astrophotography which does nothing to improve visual contrast.

4 hours ago, StarryEyed said:

I love the CONNECT that I get with visual astronomy. For example looking at Mars the photons that hit my eye are photons that have touched and bounced of its surface. Thats a real physical connection and I literally sence this I am aware of it. Same as listening to a live orchestra theres feeling there. When I listen to a recording I still have the joy of the music but I dont feel the connection with the orchestra. Same reason some people go to a football match rather tham watch it on TV. 

Astrophotography is rewarding but not it the same way. Visual astronomy makes you a participant in the universe rather than a camera man in it. If you choose the right moment for each you can actually get more enjoyment overall by making the best use of each. 

One thing is for sure a bit of visual astronomy always cheers me up no end even on the worst of days. 

Quite similar to the visceral experience of attending a Broadway/West End play/musical in person versus watching a video of it on TV.  There's simply no comparison at all.  Maybe someday with advances in virtual reality the gap will be closed; but for now, live and in-person can't be beat.

No idea how powerful my cheap, direct from China, ebay laser sights are, but they're plenty bright to see from multiple feet away in clear skies when aiming my scope.  I'm pretty sure they're not IR filtered, so I'm insanely careful using mine.  I recommend getting the laser sights with the bigger, 18650 battery instead of the smaller, 16340 battery.  I've had much better luck with them in all temperature conditions.

I've found little kids at outreach events get annoying trying to jump up and grab your laser pointer to play with like a light saber (parents need to reign in their kids, but don't), so I just don't bother with them anymore due to the risks involved.  If it's just responsible adults (no inebriated folks present), then laser pointers are fine.

I was out observing the moon last night with my 8" Dob without coma corrector (to eliminate its SA), the 3-8mm Svbony zoom, and the 5-8mm Speer-Waler varifocal.  Here are a couple of impressions from this session:

• The purple/yellow fringing was largely gone at 3mm and 4mm.  Only a small bit of yellow fringing remained in both eyepieces.  I must have been seeing violet chromatic issues introduced by the "APO" triplet at tiny exit pupils.
• Both were showing subtle mara contrast details quite well no matter where I put them in the eyepiece's AFOV.
• Both fields appeared flat of focus center to edge to my presbyopic eyes.
• 5mm seemed to be the limit of usable magnification last night.  Any higher, and my floaters got in the way, and no more fine detail was revealed in the Svbony.  Again, 8mm in both seemed best.
• The lack of a CC didn't seem to hurt axial details moved to the edge all that much with this extended object.  What was more important was slanting my view with or without eyeglasses by tilting my whole head and pulling back to get a straight on view of the edge rays.  This minimized chromatic aberrations.
• The S-W's 78° AFOV and 7-11mm of usable measured eye relief felt way more comfortable with and without glasses than the Svbony's 60° AFOV and 8mm of measured usable eye relief.  There's more to ER than what the measurements say with zooms/varifocals.
• I could still see the Svbony's AFOV receding away as I zoomed in.  The S-W didn't seem to do this all that much.  This made the Svbony's AFOV feel much narrower at higher powers than it really was.
• The Svbony's full field below 5mm is all but impossible to use for very long if you have long eyelashes like me.  I had to mash my eyelashes in the eye lens surround area to see the entire AFOV at 3mm and 4mm, and it was very uncomfortable.  I had to pull back on each eye blink to avoid getting gunk on the eye lens.
• With my 2.5 diopters of astigmatism, the views at 6mm to 8mm were subtly sharper with glasses than without despite the small exit pupils in the f/6 scope.
• The lack of parfocality of the S-W was far outweighed by the huge AFOV and slightly longer eye relief.  Much more of the moon, if not all of it at lower powers, would fit in the S-W's AFOV giving a much more satisfying view.
• The Dob didn't care how huge and long the S-W was compared to the Svbony as far as balance.  This might not be the case in a small alt-az mounted refractor, Mak, SCT, or Newt.
• Now I feel like I need to get the APM Super Zoom and pair it with a quality Barlow/Telecentric Magnifier to see if it would be the best high power zoom combination for my astigmatic eyes.

On 29/12/2022 at 13:39, tomato said:

However, after deciding that my ageing  Mk 1 eyeballs would need all the help they can get, I went for a 16” Dob which takes way more time to wheel out and set up than my dome based imaging rig, oh well…

You could build a Roll-off Dob Shed.

On 29/12/2022 at 08:08, JeremyS said:

Having looked at that ad on eBay, I now get email prompts from eBay about it 👎🏻

Always browse in private/incognito/InPrivate mode while not being logged in.  That way, no cookies get deposited on your computer long term.  If you were logged into ebay, you're out of luck.  It also prevents cross-site snooping by websites.