Louis D

You do realize that exit pupils below about 0.5 are rarely usable? As such, I would forget about the Powermate. I would put that money toward a 72mm ED refractor and mount so you can observe wide fields that your 8" SCT can't come even close to revealing. The 10mm and 12mm are fairly close. I would probably substitute the 9mm Morpheus for 226x. Mine seems to work about as well as my 10mm Delos. I don't see much if any reason to go above 306x with your scope, so the 7mm Pentax XW should be fine for nights of exceptional seeing. I have the 30mm APM UFF and both ES-92s. You'll really like them. The 40mm Pentax XW should be very good as well, although I have no personal experience with one. I use a 40mm Meade 5000 SWA (Maxvision) at that focal length. For the ES-92s, I'd check to see if you'll need to add some sort of counter balance to avoid overworking the mount.

As in ultra wide true field of view? You didn't specify the focal ratio of the 12" Dob's mirror. Assuming an f/5, that would mean 7*5=35mm would be about your longest focal length based on maxing out your exit pupil. You could go with a 30mm ES-82 or 31mm Nagler T5. The 35mm Aero ED won't be as well corrected at f/5, but it will present a slightly wider TFOV and be much lighter and cheaper.

That 12" must have been miscollimated or had a terrible mirror. My most memorable views of Jupiter were through a 12.5" Mag1 Instruments PortaBall with a Zambuto mirror on an Osypowski equatorial platform at a star party. I could make out all sorts of festoons and barges in the belts with ease.

At f/12, I wouldn't go much below 7mm to 8mm because the exit pupil becomes 8/12=0.67mm to 7/12=0.58mm which is really pushing it for most people. I would start with the 8mm BST Starguider and the 7mm SW Planetary for 188x and 214x, respectively. See how they well they work for you and go from there. I have found the 8mm BST to be a very good eyepiece. It's not Delos or Pentax XW good, but it's not that far behind despite the price difference. I have never even so much as looked through a TMB Planetary clone, of which the SW Planetary is one, but I've read that many find them to perform quite well. You might even want to consider the 9mm SW Planetary instead of the 7mm to back off the power a bit to 167x when conditions won't support 214x.

Generally, Barlowing binoviewers works really well because it helps to reach focus in telescopes with limited in-focus travel, slows down the light cone, and seemingly makes merging high power images easier than when using pairs of short focal length eyepieces. Even with SCTs and Maks that can natively reach focus with binoviewers, Barlows allow the telescope to operate much closer to its designed focal length which minimizes induced spherical aberration. All in all, Barlows play really nicely with binoviewers.

I did one thing right starting out 23 years ago. I attended public star parties for 2 years before deciding on the type and size of telescope I wanted to use. That was a 6" to 8" Dobsonian solid tube telescope. I was even looking through 4" Astro-Physics refractors on really nice mounts, but I was completely unimpressed by them compared to the bigger Newts. SCTs of the day seemed to put up really mushy images aperture for aperture compared to their Newtonian counterparts. They all couldn't have been out of alignment. No one was observing with Maks or traditional Cassegrains back then that I can remember, so those were never considered. I also realized nudging to track wasn't that big of a deal. Neither was learning the sky via sky atlases and star hopping. There were a few fledgling planetarium programs out there, but there were no smart phones or tablets to use them on while observing. Vastly expensive laptops were the only portable electronics option, but I didn't have one and couldn't afford one, either. I also realized I needed long eye relief eyepieces that work well at f/6, so I bought Vixen LV and Pentax XL eyepieces and skipped the whole eyepiece upgrade treadmill. Vixen LVWs and long focal length Panoptics were about the only other well corrected, long eye relief options back then. There are so many more high quality options today at much lower inflation adjusted prices that folks starting out today don't even realize how lucky they are compared to the situation just 23 years ago. I can't even relate to those who started out in astronomy in the 1950s to 1970s. Everything seemed so rudimentary and yet so expensive at the same time based on the ads I've seen.

The equation for Barlow magnification is M = 1 - L / fb where L is the distance from the Barlow lens to the eyepiece's field stop and fb is the Barlow focal length (always a negative number for magnifying Barlows). Regardless of the Barlow focal length, which is never reported by any Barlow makers to my knowledge, it is clear that increasing the working distance between the Barlow lens and the eyepiece is going to increase the magnification. That's why using Barlow elements in front of a binoviewer generally yields more magnification than when the Barlow is used as designed. This assumes that the Barlow had a shorter working distance as designed than the optical path length of the binoviewer. There are vintage long Barlows for which this might not be the case, but they didn't generally have removable lens cells.

If quality, low cost ED refractors had been available in 2000, I would never have bought my ST80. Horrible purple fringing and spherical aberration along with a mediocre focuser. I had hoped it could double as a spotting scope, but the haziness of the view was more than I could take. In the end, it has sat mostly unused in the closet for 20 years. I ended up paying about the same 13 years later in inflation adjusted dollars for my used AT72ED which blows the ST80 out of the water in every way except weight. I actually paid much more for my ST80 in 2000 than they sell for new today!

At least it looks great if you want to sell in on. 😙

Doubly important when using binoviewers because you're trying to swap two eyepieces at a time and trying to avoid letting them tip in the collets due to undercuts.

I've never heard that it matters, just don't overdue it when tightening them. Hopefully a few others with more knowledge than I in this area will chime in.

Given the tight supply constraints on new telescopes and mounts right now, you'll probably have to start out seeing what's available from various dealers such as Astronomics up in Norman, OK. I know that would just kill a true Texan to buy from a Sooner retailer, though. 😄 They do sponsor Cloudy Nights forums like FLO sponsors SGL here. There's also Agena Astro, OPT Telescopes, Orion, Skies Unlimited, High Point Scientific, and several others. I would avoid the NYC mega-retailers because telescopes are just a side business for them, and they have very limited expertise with them. For what you want to look at, a computerized mount might just get in the way. You would probably want to stick with an alt-az (up-down/left-right) mount for whatever telescope you end up purchasing. I would avoid a fast (short/low f-ratio) achromatic refractor. They generally have loads of color fringing and spherical aberration. A slow (long/high f-ratio) achromat can become a bit unwieldy for terrestrial use. A smallish Mak or SCT might suit your needs well. Really, it comes down to your budget, storage room, ability to transport, observing site restrictions, etc. Ideally, a fast 4" apochromatic refractor might serve you well, but might also be too expensive.

They should be left "totally" loose for normal visual astronomy when using the built-in focuser. They're mainly there for transporting the telescope and to lock up the mirror during imaging (as when a secondary focuser replaces the normal visual back) to prevent mirror shift as the telescope changes orientation while tracking across the sky. If you lock up the mirror and try to focus using the built-in focuser, you're likely to break or bend something because the scope focuses by moving the primary mirror.

If you do decide to keep it, regardless of cleaning it, document the undisclosed fungus with macro photos clearly showing it and demand a commensurate refund of part of the purchase price as compensation for your troubles.

It will vignette the light path more as you would expect. Most Dob filter slides are 2" for this reason.

The 22mm NT4 comes up used quite often here in the states for about $300 give or take $50, so you might want to check the classifieds over there for one. I picked up mine for $250 just a year ago.

I'm pretty sure it's 75mm from the sensor or eyepiece field stop to the top of the M48 threads on the optical nose piece. You may have to adjust it a bit to find the optimal spacing. I have the High Point (now Apertura) version, IIRC.

Hopefully @Don Pensack can chime in here having owned and used both. In the meantime, I found the Ethos restricted to about 70 degrees with eyeglasses at star parties. When I took off my eyeglasses, ignoring massively astigmatic stars, I had to push my eye into the eye cup to see the entire field. That does cut off any perception of the non-eyepiece FOV world. Comparatively, my ES-92s are very relaxed and seem more like looking out a bay window from up close. The 22mm T4 views similarly, just through a smaller window. You're aware there's a world surrounding the view due to the more generous eye relief. It is possible to raise the Instajust eye cup if you want a more Ethos-like experience of excluding the outside world, just with a smaller AFOV.

Certainly if you wear glasses the 22mm NT4 is a good alternative. It's what I ended up with at that focal length. The difference in field stop diameter is negligible between it and the 27mm Panoptic. They feels worlds different in usage, though. The Nagler is just so much more immersive and easier to take in the field stop with eyeglasses than the 27 Pan. The 30mm APM UFF is noticeably wider than either having a field stop over 5mm larger in diameter, making it just about the same TFOV as the 21mm Ethos.

The working distance is around 75mm as you say. It magnifies 1.10x (10%). I usually only use it visually. I did use it to capture the 2016 Mercury transit image below, so I know it can be used with DSLRs.

Much prefer my 30mm APM UFF to my 27mm Panoptic. Better eye relief, better edge correction, flatter field, and noticeably wider TFOV. The Pan might have a slight edge in on-axis sharpness, but it is very slight. I can't use any 100 degree eyepieces due to my strong astigmatism in my observing eye, so no comparison possible for me vis-à-vis any Ethos.

Unless you're using a Newtonian with limited back focus, you should be able to do DSLR prime focus photography with a 2" to T-thread adapter and a T-mount for your camera. If you're using a Newt with limited back focus, you can try to use a 2" Barlow or a GSO/Revelation coma corrector with the optics section threaded onto the front of the 2" to T-thread adapter. You won't be able to vary magnification much except with the Barlow approach.

Try to get it on APOD?

🤔 12mm ES-92 is 2" only. There are also the 5.5mm, 9mm, and 14mm ES-100 eyepieces as well as the 9mm ES-120. I can't think of any 6mm, 8mm, or 10mm 2"-only eyepieces, though, as you say.

Are you thinking using a 2" to 1.25" Filter Adapter? If so, let us know how well it works for you. I haven't read any actual reports on their usefulness.