Louis D

Since I had a bit of time on my hands, I went ahead and composited the various AT72ED f/6 zoom images into a single image below: The individual images are each at full resolution. You can see how both image scale and AFOV shrinks with increasing focal length with traditional zooms. However, the varifocal SW has a constant AFOV from one end to the other. If you open the image to full resolution, you can see how the traditional zooms are very sharp at the longest focal length. They get less sharp with decreasing focal length. The SW stays about the same. However, SAEP grows more severe with decreasing focal length in the SW. This matches with my experience that the more Barlow extension you use, the more SAEP that gets introduced.

You can see how my two traditional zooms stack up against fixed focal length eyepieces in various images in this post of mine: If you open up the individual images in a separate tab, you'll be able to examine the full resolution images in detail after expanding them. Honestly, the zooms hold up at least as well as Plossls, if not better. They're certainly better than the various Kellners, MA, RKE, and 25mm Ortho eyepieces in those images. The SW Zoom spanks most of the other eyepieces, but it should for the original price I paid (about $400 in today's currency). It's more of a varifocal, though, in that it is not at all parfocal.

If that tripod has the plastic leg clamps, make sure to avoid overtightening them because they will crack and become useless.

Another good step-up zoom to hunt for used or NOS is the Celestron Regal Zoom 8-24mm. It was also packaged with the equivalent Olivon spotting scopes. The latter come with a rubber grip instead of metal ridges as with the Celestron. I've picked up multiple copies for about $65 each over the years from CN classifieds and ebay to keep with various scopes or in the BV case. They do lack filter threads, but the top doesn't rotate while zooming. This is important if you swap in winged eye cups while binoviewing. The standard twist-up eye cup screws right off after twisting all the way down, revealing an M37 thread making eye cup swaps easier. It also maximizes eye relief for eyeglass wearers like me. I use a pair in my binoviewer. Some versions zoom smoothly while others I've gotten are stiff to zoom. They come in several different marking variations depending on which spotting scope they were sold with, or if they were sold stand-alone. I find them easier to use with eyeglasses than the BHZ. They're not quite as wide at the short end (about 63 degrees) as the BHZ, but it still feels quite wide. They're 45 degrees at the long end, so an improvement over the cheap Celestron 8-24mm zoom. They reasonably parfocal, but certainly not perfect. The field stop is sharpest toward the middle of the range. The edges aren't perfect even at f/6, but they're not that bad, either. The central region is quite good throughout the zoom range. If you can pick them up for cheap on the secondary market, they're quite a good deal.

Here's a brief review of the Orion on CN.

Yep, that's a GSO dielectric. I've got them under the TPO and ScopeStuff labels as well.

You can definitely do DSO astrophotography with a dual axis equatorial platform as well. In fact, if you're using a 12" or larger Newt, I would recommend to go that route over an enormous GEM EQ.

Does it have the restriction at the bottom of the eyepiece holder like the 1.25" version?

I just use SkEye on my cellphone while mounted to the OTA. After alignment on an object, the map moves with the scope, and I just two finger zoom in to see what I'm pointing at (or close to since there can be a few degree error). Works well enough for free for me.

EQs track, Dobs can too with either an EQ platform or alt-az motors and computerized control. EQs weigh quite a bit more than an equivalent alt-az mount due to the massive counterweights for a 200P. EQs are insanely top heavy once assembled, so next to impossible to safely move around the yard to dodge obstructions unless mounted on a dolly/wheeley bars/etc. Dobs are bottom heavy and quite stable. They can be moved around assembled by penguin walking them while hugging them close to the body. The focuser rotates into awkward orientations on an EQ for Newts if lacking rotating rings. It's stays in pretty much the same orientation for Dobs. You need a really beefy EQ mount to handle a 200P that can cost well more than the OTA.

So, will the mount slew to where it thinks the first alignment star is located based on the initial zero position? I've heard that's how some of these mounts work, which is pretty neat for beginners who don't know alignment star names and locations.

I'd recommend checking the classifieds for a GSO 2" dielectric. I've got three of them under various brands that I keep with various scopes. They are not light, though. I don't think I paid more the $70 for any of them. Admittedly, used prices and availability may be different in the UK/Europe.

I wonder why the need to pre-align the mount? I've never had to do leveling or aligning of my Sky Commander DSCs on my Dob, and it's fairly accurate after two star alignment and gets better with each object realignment once centered.

Achro, ED, or APO? A 60mm f/11 achromat was the traditional entry point for astronomy for most of the 20th century. I have a 72mm ED that is much more compact with slightly more aperture. I really like its compactness and ability to accept 2" eyepieces. Wide field views are fabulous with it.

Well, Brandon eyepieces didn't seem to pass on the cost savings of single coating. These 4 element eyepieces are $280!

Yeah, but all the cool kids have BCLs. 😉

I couldn't use my ES-92 eyepieces in my refractors or Mak without one, so there is that. However, for binoviewing, I use a 1.25" diagonal to keep the optical path shorter than in a 2" diagonal. Using my 24mm APM UFF or 32mm GSO Plossl as a widest field eyepiece instead of one of my 30mm to 40mm widest field 2" eyepieces seems unnecessarily restrictive just to keep an eyepiece collection simple or to avoid balance issues. Sure, my A-team eyepiece case weighs in at over 20 pounds, but there's a lot of observing joy packed in there. I know someday I won't be able to hoist that weight, so I may have to split it across multiple cases.

I prefer the 30mm APM UFF to my 30mm ES-82 for both eye relief reasons and for image quality. The latter has a bit bloated stars on axis and severe CAEP at the edge. The APM has none of this. My 27mm Panoptic might be a tad sharper on axis, but the APM trounces it for eye relief, field flatness, and edge sharpness.

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TV eyepiece specs for 20mm NT5 (see the column right of C, 12mm ER): EN5-20.0 20 Nagler 5 (disc) 2" 6 / 4 82 C 12 27.4 2.1 1.3 2.1 0.15 1.04 / 16.6 Y* So, not a good choice for the OP who seeks a minimum of 15mm eye relief. I was going to recommend it myself until I checked TV's specs and ruled it out.

Are the types of fisheye mappings applicable to eyepiece distortion?

The Lacerta ED 40mm also claims to have a 69° AFOV while in fact it has a 65° AFOV and a 66° eAFOV. It's focal length in the center is 40.1mm and 31.1mm radially at the edge by my calculations. Once again, like the 35mm Baader Scopos Extreme (70° claimed AFOV, 66° measured AFOV, 68° eAFOV), and 26mm Meade MWA (100° claimed AFOV, 83° measured AFOV, 90° eAFOV), the 40mm Lacerta ED (TMB Paragon) is targeting the AFOV of its benchmarked competition (35mm Panoptic for the Baader, 25mm ES-100 for the Meade, and 41mm Panoptic/40mm Pentax XW/etc. for the Lacerta/TMB). It's quite easy to see below that the Baader is not 70° and the Lacerta is not 69° despite claims on either their barrels or in their marketing literature: The Baader has a center focal length of 34.8mm and a radial edge magnification of 28.8mm, so only a 17% difference versus 22.4% for the Lacerta. Thus, even more "orthoscopic". The 40mm Meade Series 5000 Plossl is also low distortion at a 21.2% difference (40.4mm vs 31.8mm). The edge does get pretty blurry at f/6, but the moon looks quite naturally round across the field in it. A bit more magnified, you can see that there is some magnification distortion in the Lacerta at the edge, so it's not perfectly orthoscopic. It's less than the "competition", though.

Probably 65° eAFOV. My Meade 5000 SWA, Pentax XW-R, and Lacerta ED 40mm's are all 65°/66° eAFOVs despite having 69°, 70°, and 65° AFOVs, respectively. If the Vixen LVW has a field stop of around 46mm +/- 0.3mm, that's the most likely explanation.

I wonder if the Lacerta ED 40mm (TMB Paragon) is better, worse, or the same corrected as the 42mm Vixen LVW? 🤨

It's probably far enough above the focal plane that it won't be very visible. On the other hand, I had a brand new 30mm APM UFF with debris on one of the lower lenses which is practically coincident with the focal plane, and boy was that visible. In the far right schematic below, the debris was on either the top of the second lens from the bottom or the bottom of the third lens up from the bottom. Both are rally close to the internal field stop. Either way, I exchanged it for another that was clean.