Louis D

Yes, focusing an SCT or Mak generally moves the primary mirror unless you've opted to add a Crayford style focuser to the rear port. To move the focus position further from the back plate, the mirror must move forward toward the corrector. This extends more of the light cone behind the back plate. I would think this would also cause some vignetting because a wider portion of the light cone is hitting the secondary and passing through the rear port. Yes, you have to position the mirror to provide best focus, and if you move the position of the eyepiece back 100mm from the rear port by adding a BV, that means best focus has also moved back 100mm from the rear port.

Try the experiment again without the reducer in place. See if the level of astigmatism gets better or worse at the edge. You may also notice increased field curvature or possibly coma (IIRC) without the reducer/corrector.

None beyond what effect they have on SCTs and Maks in native focus mode without an OCA/Barlow. That is, to reach focus with a BV in a catadioptric scope without an OCA/Barlow element requires about 100mm or more additional back focus. To do this, the primary mirror must be shifted forward which increases the scope's focal length due to the magnification factor of the secondary mirror. There are formulas for both types to calculate the added focal length based on added back focus.

You could try using a 0.63x focal reducer/corrector. That way, you get to roughly the same widest field by using a widest field 1.25" eyepiece with it without having to invest in a 2" diagonal, 2" visual back, and 2" eyepieces.

That comparison only speaks to the quality of Long Perng made eyepieces in general since the OP asked about the 68 degree line, not the 80 degree line.

According to Ernest's measurements, the 16mm Levenhuk Ra UWA 82° branding of the 16mm Nirvana 82° has a 25mm diameter field lens and a 21.2mm field stop. Technically, it wouldn't vignette based on the field stop alone, but since the field lens is slightly larger than the BV's clear aperture (~22mm), there might be a bit of vignetting at the edge. Since you have to look in the center to hold both images, you'd be unlikely to see this level of vignetting in your peripheral vision, though.

The Altair Lightwave Premium LER 68 is the same as FLO's StellaLyra 68º LER / WA. Here's a recent thread on it and the StellaLyra 80° LER / UWA: Ernest in Russia tested the entire line 68º here under the Levenhuk Ra ER20 WA branding.

I forgot to mention I need to wear eyeglasses when observing with exit pupils larger than 1mm, so that limits my choices. Microscope eyepieces intended for eyeglass wearers are also a good choice if you can get the proper barrel adapters. They are generally compact and designed to be very sharp at f/18. If you don't need to wear eyeglasses, you have many more options.

I've recommended it many times before, but here it goes again. Look for a used, vintage Meade 140 2x Barlow to use as an OCS/OCA/GPC. They regularly go for between $40 and $65 over here on our astro classifieds. The nosepiece is a three element, filter threaded unit that can be screwed onto the front of a WO/Arcturus/etc. BV. It operates right at 3x in that configuration and is insanely sharp. I have no trouble reaching focus in my Dob that has a low profile focuser and 20mm of in-focus left with eyepieces that focus at the shoulder. It also works great in refractors to avoid having to rack the focus in from its normal focus position. Since I only view planetary sized objects with BVs, the 3x magnification is a plus.

If you are going to be using a 2x Barlow nosepiece operating at that or even a higher power, you can get away with using lighter, cheaper eyepieces. I've found Svbony 20mm UWAs work really well at 3x (f/18 in my scopes). I can't get my nose between fat eyepieces like the Morpheus. That, and two of them plus the BV weigh a lot.

You need to remove length from the OTA if you run out of in-focus. Some refractors come with rear sections that can be unscrewed and removed to shorten the overall tube length. Before blaming BV alignment, try checking that neither eyepiece is tipped in its holder due to undercuts. Next, rotate the diopter adjusters to see if the images demerge due to lack of concentricity in the adjusters.

Sounds an opportunity for a future improvement by Celestron.

That could very well be the case, especially being prefaced by electronics rather than optics. Mea culpa. I've got optics on the brain, apparently. 🤪

I couldn't find anything in the manual about realigning on objects once centered in the field of view. My decades old Sky Commander DSCs (section 5.7 Realign on Object Menu) and the much newer SkEye app (section 3.3.4 Adding more Alignments) both have the ability to tell it that the object is centered in the main telescope, and thus to adjust its alignment to compensate. Did I miss something in the Starsense manual about how to do this?

The AAAS article referenced in the linked story makes a common mistake: Researchers are bringing into focus novel electronics such as systems on plastic, which are deformable and implantable, zero-power, and wireless and have numerous applications for sight and vision. I'm pretty sure they meant unit-power (1x), as with Telrads and QuikFinders. Zero-power (0x) would act as an infinite telecompressor and make everything infinitesimally small, which I doubt anyone would want or have a need for. Sort of a black hole in effect.

Just get in there with a flat black ink pen and darken the edges. 😉

Sounds like the perfect project for a 3-D printer.

SL 1113 may have been built as a spare and never flew. At some point, it was probably surplussed, leading to your acquisition.

You have been assimilated.

Those Starlink satellites are pretty intrusive during twilight. Hopefully, bringing broadband to underserved parts of the world will make it worthwhile. Apparently, it's already been helpful in Ukraine.

Probably the job of the thread-on eyepiece holder that was removed. Why someone would have unscrewed it all the way off is the real question. Maybe the previous owner's kid did it?

Try a 12mm Nagler Type 4. It is extremely fussy to take in the entire field of view. The moment the field stop pops into view, blackouts start raging around the field of view. The 12mm ES-92 is much better behaved in this respect. I've not noticed that the 7mm and 3.5mm Pentax XWs are any fussier than my 5.2mm and 14mm Pentax XLs, 9mm and 14mm Morpheus or 10mm Delos. I do wear glasses at the eyepiece, so I always have a reference distance thanks to them. That may help with eye placement stability.

Not so much still available as a new production run. Notice that the 35mm ED is not available from Lacerta. Apparently, they decided it wouldn't be a good enough seller to add it to their production order.

The Altair version is reportedly heavier due to having a stainless steel barrel. The APM version uses aluminum. My 30mm APM UFF weighs 548g by my scale. Good job snagging it for half retail.

Meade had their MWA line which I assume stood for Mega Wide Angle. They claimed 100 degrees, but delivered somewhere between 80 and 90 degrees, depending on the focal length. The eAFOV was around 90 degrees due to barrel distortion.