Louis D

Above 10", I would seriously consider going with truss Dob. Weight and tube size take a serious jump at 12"

For low power views they would probably be fine. You could always add a Baader Contrast Booster to suppress all purple and deep blue light if the color fringing bothers you. At high powers, their chromatic and spherical aberrations would detract from the view. It really depends on what you want out of a refractor.

What's the issue? Since it focuses below the reference plane (eyepiece shoulder), in-focus shouldn't be an issue. It's also well corrected to at least f/4. Is it just the large exit pupil bothering you? It should still work well as a finder eyepiece, just with a washed out background sky.

A big ole Howdy Pardner from Texas!

Agreed @JTEC. I couldn't get my 19mm Russell Konig pair to merge at all last Friday despite my best debugging attempts, so the new SVBONY 20mm UWA eyepieces replaced them in the BV case.

Well, except for the fact that BVs are firmly attached to a large object making eye/BV alignment a much bigger challenge than with handheld binoculars. With cyclops viewing, it doesn't matter at what angle you come in at the eyepiece or even if your face is square on with it. All this matters immensely with BVs. As such, I have to get my observing chair "just so" in front of the BV so I can comfortably align my head and eyes to the BV. I can rotate the BV in the focuser, but I can't tip them up/down or swing them left/right because, again, they're attached to a large object, the OTA. As such, I have to be really motivated to get them out. Things like planetary oppositions and such motivate me. For casual panning about the skies, I prefer monovision.

Make sure to give that triplet plenty of time to acclimate. I have to allow 30+ minutes for my 90mm triplet to equilibrate before the spikes around stars settle down. The first time I looked through it, I freaked out thinking it had pinched optics. It just needed time outside to settle down.

Agreed on GCs and BVs. I had very relaxing views of M22 last Friday night. I don't know that I could make out any more stars across the core in bino vs mono mode, but the steadiness of the view improved with two eyes such that I could study it more easily.

You might like the 17mm ES-92. It gives up very little in TFOV to the 22mm NT4 while still being easy to use with eyeglasses. The whole AFOV is easy to take in. It's just there in front of your eye like a big picture window. IIRC, I bought my 22mm NT4 from a seller who replaced his with a 17mm ES-92. I like them both, so I've kept both.

Do you have astigmatism in your observing eye? If it is greater than 0.5 diopters (check CYL section of your eyeglass prescription), you'll want to either wear eyeglasses or use a Dioptrx. If this is the case, the 22mm NT4 comes highly recommended. If not, you could go with the 21mm Ethos or a 20mm APM XWA HDC (or other brandings) if cost is an issue.

Well, I'm guessing from your avatar that you already have an 8" Dob. A 3" to 4" ED or APO refractor can nicely complement such an instrument for wide star field views, splitting tight, uneven double stars, etc. thanks to their tight star images. I would suggest starting with an ED doublet because triplets are very slow to acclimate. Cheap, short tube achromats often have loads of spherical aberration and purple fringing. I was put off by my ST80 because of both. My 72ED changed all that. I then moved up to a 90mm FPL-53 triplet for more general use. However, I have to think ahead and set it out the equilibrate, or I'll have spiky stars for 30 minutes or more. The 72ED does not have this issue being a smaller doublet.

That, and the weather is cool in the summer with low humidity. Winters are fairly mild by mountain standards due to being so far south and surrounded by desert.

Yes, a ruler. I did an analysis of photographed field versus known good field values from Televue and other online sources for eyepieces I own. I arrived at a best fit coefficient to convert the photographed distance to the field stop value in millimeters. Error can creep in whenever I setup again (I try to get the distance correct to with less than an inch over 35 feet or about 0.002% error). A bigger error creeps in because I eyeball the distance which can allow me to see more than could be seen from the center by swiveling my eye and looking to the side. As the image fades off to black for eyepieces with poorly defined field stops, where do you declare the actual field stop edge? This is an even bigger issue with eyepieces having massive chromatic aberration at the edge. Is the edge where all colors are present or where the last color is present? Should field stop be defined as the edge visible from the center of the eye lens or is peeking in from the edge of the eye lens allowed? If I had a 24mm Panoptic, I'd probably be able to get a much more accurate field stop number for the 24mm APM UFF using differential distances and the official FS value from TV. However, it's tight eye relief precludes me from buying one. I went back to my images and recalculated the 24mm APM UFF as a percentage of the 27mm Panoptic's 30.5mm field stop (TV specs) since I have images of both and arrived at 27.2mm for the APM. Your 27.3mm value is probably right on the money.

I would think you would want a combination of foil underneath and closed cell foam above to combat both radiational and convective cooling, respectively.

Supposedly, the prisms in the ADC units correct the entire field. I would think the software method would work the same way. There is some variability of AD from top to bottom in wide field shots (more than a couple of degrees), so software would have to accommodate them for best results. However, AD may not be visible in truly wide angle images.

Are you saying red/blue fringes on either side of best focus or more like AD above when in focus? It's not unusual for APOs to have red or blue fringing on either side of best focus. It's the nature of the beast.

Here's a good example of AD before and after being corrected either in software alone or with an ADC and software:

For the 24mm APM UFF, I measured the AFOV to be 63° and the eAFOV to be 66° (27.5mm field stop diameter). For the 30mm APM UFF, I measured the AFOV to be 72°/73° (projection/photographic) and the eAFOV to be 70° (36.4mm field stop diameter). Thus, one must have edge compression while the other edge expansion. In use, neither is all that noticeable. The 24mm's edge vignetting/fuzziness right at the field stop is noticeable, though.

You may want to invest in a 0.63x reducer/corrector instead for photography. It would reduce your f-ratio to f/6.3 and focal length to 1260mm. This would help ease your way into astrophotography with it.

I took the elevator to the Sphinx observation deck back in '93 when I visited the Jungfraujoch with my wife. The view is quite spectacular. I've got to wonder though, how many clear nights a year do they get? I'm looking at buying a second home near Cloudcroft, NM. Just to the south is the Sunspot Solar Observatory and Apache Point Observatory and to the east is the Remote Astronomical Society Observatory of New Mexico and Stars End astronomy subdivision.

False binoviewer collimation issues crop up from eyepieces tipping in the holders thanks to undercuts, and from diopter correctors not remaining concentric while being spun upward. Most binoviewers come very well collimated from the factory, so look at everything else if merging is an issue.

@Tiny ClangerIf you've studied the StellaLyra, you've studied the GSO. They're the same. They're sold around the world under many different brand names (Apertura/Zhumell in US). Just like the JOC Dob is sold as Explore Scientific and Synta is sold as Orion as well as Sky-Watcher in the US.

Nearby or in general? In general, parts of the American Southwest have excellent seeing conditions for the majority of the year. There's even an area of Mayhill, NM, dedicated to astro enthusiasts. NC deals with a lot of bad weather year round, so you're going to be up against it regardless of location. I would guess coastal areas would have better seeing, being far from the turbulence induced by the Smokies to the west. The Florida Keys have some of the best seeing conditions on the east coast of the US if you're thinking of a second home for astrophotography.

GSO is GSO from Taiwan, Bresser is JOC from China, and Skywatcher is Synta from China. If you want European or American made, you're looking at a premium Dob costing many thousands more. To be honest, many of GSO's components are rumored to be sourced from Chinese factories for cost reasons. I don't know if anyone has ever done a comprehensive test of the mirrors shipped with each telescope. Usually, they're considered pretty decent, but not exceptional. Mechanically, the Bresser/JOC will probably be best with the large altitude bearings. I'm not a big fan of GSO's lazy Susan azimuth bearing because it can foul with ground grime and because it offers no "sticktion" to hold its position. Teflon riding on a pebbly surface has been the gold standard used by custom Dob manufacturers for decades. I have no idea, though, what the JOC azimuth bearing is. I was unaware that the Bresser/JOC focuser had the ability to be upgraded to two speed, so that is a definite plus. The GSO focuser is generally well regarded, especially as compared to the SW/Synta version. None are going to be Feathertouch level refined, but it would cost as much as the scope as a whole in India. At 10 inches, a proper mirror cell becomes important unless a center mounted conical mirror is used, and the JOC would seem to win out in this regard. Don't underestimate the weight and bulk of a 10" scope as compared to an 8" scope. It's a not insignificant increase. That, and the f/5 mirror will be significantly more demanding on eyepieces than an f/6. You'll also probably want to invest in a coma corrector at f/5, whereas at f/6 coma is less intrusive.

This one?