Louis D

So make sure to bring a correct image 45° or 90° prism diagonal as well for the frac for daytime usage. You could even bring a binoviewer to reduce eye strain.

If you're handy, you could rebuild your Dob into a suitcase Dob.

But did you remember to bring long lasting photovoltaic cells? Are wiring and plumbing bits available to create a steam generator for electricity? I suppose you could bring a mechanical clock drive mechanism:

The AT AF70 (Omegon Redline SW) have an excellent 22mm, an okay 17mm, an iffy 13mm, and reportedly (I haven't tried these personally) mediocre 8mm and 5mm versions. Thus, you can't extrapolate eyepiece performance across an entire line based on the performance of one of them. That's why I pick and choose the best eyepieces from different eyepiece lines.

I'd probably go with a refractor on a desert island because sea salt mist would eventually corrode mirror coatings even with a protective oxide overcoat. A weatherproofed SCT or Mak spotter might also be an option. Probably a ruggedized and sealed 100mm spotting scope would be a good choice since repairs would be all but impossible. I suppose if the desert island were large enough with a decent elevation change, you could get away with a non-sealed reflector used in the island's interior.

Yep, I have the TV 2x Barlow as well, and its nosepiece threads are smaller than 1.25" filter threads, so it's a no-go to use it as an OCS/OCA/GPC.

Look for a used Meade 140 2x Barlow. The nosepiece unscrews from the tube and can be screwed onto the nosepiece of the BV for right at 3x. They have super sharp, 3 element Japanese made optics.

With a fast achro, the Baader Solar Continuum filter would help immensely since it filters out the unfocused ends of the spectrum leaving only the sharp green portion around 540nm: Even a #56 Green filter would probably help immensely to increase image sharpness in an achro: Passing only 50% of the green light isn't a big deal with solar viewing since you're attenuating it so much anyway.

I think it might just go into a state of suspended animation like a tardigrade does.

Did it come with a 45° correct image prism diagonal? If so, you should swap it out for a standard 90° mirror or prism diagonal at some point. Have a look down the front. Is there an obvious circular aperture stop directly behind the objective? I ask because I picked up a similar looking 70mm "travel" scope off ebay two years ago, and it had stops in both the main tube and the focuser tube. They stop down the objective to about 35mm at most to improve the image quality at the expense of light gathering. You might want to get a #12 yellow filter and #56 green filter to block unfocused violet-blue light with the yellow and blue and red with the green. I found they help on planetary details with my ST80 scope. Of course, the color balance is way off while you use them. An achromat such as your scope only focuses light from teal to yellow-orange well. The unfocused light can degrade the image at high powers, thus the filters.

Indeed. It's exit pupil based. The problem with smaller scopes is image scale. At the preferred exit pupil, the nebula image will be smaller than in a larger aperture telescope. If you're willing to live with a smaller image scale, the OIII will work fine in smaller scopes. In fact, you might be able to detect large nebula regions thanks to the wider field of view at larger exit pupils. By contrast in larger aperture scopes, you just can't get the magnification down low enough to do edge detection on these same regions. You end up looking straight through them as if they were mere sky glow. You might detect them with careful sweeping of the area, but detailed observing would be difficult.

Not surprising. It says right on the linked webpage: Designed and manufactured exclusively for Tele Vue by Astronomik.

About $14 at today's pricing here in the States (see added links above). Less facetiously, I quote from the quartz diagonal's description linked above: High quality diagonal mirrors are usually made of BK7 glass. Quartz glass goes a notch higher - it offers greater thermal stability, resulting in minimal thermal expansion and contraction as compared to other glass types. The result is a minimal, if any, shift in focus due to temperature changes over long observation sessions, making this quartz diagonal ideal for photographic and imaging applications. I can't say that I've ever noticed the difference. I just picked up the used quartz version because it was being offered for the same price as the used regular glass version. I wouldn't have picked it up otherwise. Who would image through a diagonal? Who observes long enough at one focus setting to notice thermal shift? If the difference is only $14 at the retailer, it's probably much less at the manufacturer and could become the standard if used in all diagonals which would further drive down the price differential through economies of scale. However, it's a case that no one would ever notice the difference; so why drive up the price, even slightly, for every diagonal just to have quartz in it? It's just a marketing ploy in my opinion.

Theoretically, as long as the passband is perfectly centered on the emission line(s), the narrower passband filters should simply exclude more stray light increasing contrast. However, you run into the problem that there are two OIII emission lines, a brighter one at 500.7nm and a secondary one at 495.5nm. Most visual OIII filters attempt to pass both while most ultra-narrowband imaging filters only pass the former. It would be great if the filter could pass each with a 3nm passband, but that's not really possible as the two passbands would be touching at their bases, and it would be super expensive to manufacture. Instead, most use a 12nm to 15nm passband for visual to pick up both bands to increase the signal being fed into the eye at the expense of passing more sky glow noise.

I have the same diagonal in both regular and quartz, and I have never had any issues with stray reflections on bright objects causing odd halos or other artifacts as they enter and leave the field of view. On the other hand, I do need to flock the rear baffle tube of my 127 Mak because I do get odd halo inducing reflections off of it with a 2" diagonal as bright objects pass the edge of it. Maybe you'll say the surfaces cause some amount of contrast decreasing scattered light, but so do the shiny filter threads on many eyepieces, and I've never heard of anyone calling for a ban on shiny filter threads. Some others start out blackened, but it grinds off pretty quickly using filters regularly. I'll take my chances with stray light with these GSO diagonals over having a restricted light path with my widest field eyepieces in those other diagonals of unknown manufacturer (Synta?).

I can't get the BST Starguider/AT Paradigm eyepieces to decloak. The eyecup just pulls right off, and the lower ring and color ring unscrew easily enough, but the big metal band that twists the eyecup support up and down seems stuck in place. If you come across detailed instructions, I'd appreciate it. There's a thread on CN about decloaking them for binoviewer usage. IIRC, It's fairly straightforward to unscrew the lower ring of the adjustable eyecup, and then just lift off the rest. It helps those with deep set eyes and tall nose bridges like myself. 15x long eye relief microscope eyepieces are about 17mm while 20x ones would be about 12.5mm. They're designed for binoviewer usage and very slow f-ratios (f/18, IIRC). Some Leica and Zeiss eyepieces have excellent polish and correction. You would just need to adapt them to a 1.25" barrel. I have been using a pair of vintage Bausch & Lomb 15x WF eyepieces in my binoviewer to good effect for years. I had a machinist make 23mm to 1.25" adapters for me. 3D printing would also work well for this purpose. A pair of zooms would be another option. Eye relief might be a little tight, but you can easily change magnification to match seeing conditions.

Can I ask why you bought another scope barely different from the FS60CB aperture-wise? For my second refractor after my 72ED, I went with a 90mm APO FPL-53 triplet, and it made a big difference in reducing spurious color at high powers. However, cool down time increased dramatically. I really like the R&P focuser on the APO for securely lifting heavy loads at high altitudes as well. The smooth Crayford focuser on the 72ED slips horribly with 3 pound loads in it no matter how much I try to tension it.

I can't get my fairly narrow nose bridge between a pair of eyepieces in the Hyperion width class, so double check your width tolerance. I'm surprised the Plossls aren't sharp at f/10. Most Plossls are pretty decent at f/6 and really good by f/12. Perhaps it's the level of polish on them that makes the difference in your case. I would probably start with a pair of longer eye relief 22mm to 26mm Plossls or similar and put a 1.6x to 2x Barlow nosepiece or similar OCA/OCS/GPC on the front of the binoviewer to get to higher powers.

The 130PDS would probably be excellent for wide field viewing, but the 5" aperture would be a bit limiting on DSOs. At f/5, collimation will be more critical. The secondary is oversized for visual use to avoid vignetting while imaging. As such, it will decrease planetary contrast somewhat. If you go the EQ mount route, don't forget how top heavy they get with an OTA and counterweights attached. It makes moving the fully assembled system about the yard to avoid trees, bushes, and houses really difficult compared to a similar weight Dob. You just pick up the bottom heavy Dob and hug it close to your body while penguin walking it about. I once looked at buying a used 127 Mak on a smallish EQ mount and couldn't believe how heavy it was fully mounted. I went the alt-az mount route instead to avoid counterweights.

Since your work was published in Astronomy Now well before the Rowan kit was offered, it is now prior art; and Rowan would have to limit the scope of any patent because of your prior work. Kudos to you for keeping your efforts in the public domain.

Interesting. Their LV and NLV predecessors both had undercuts. I guess when they moved production to China, they also removed the undercuts.

Yes, it does work to use 2" accessories on a 127 Mak. You do get gradual vignetting toward the edge as is visible in the Meade 40mm SWA part of the image below. You do get a much wider true field of view than is possible in a widest field 1.25" eyepiece as with the 24mm APM UFF part of the image. The eye is very forgiving of gradual vignetting. I do get an odd reflection from bright objects once they pass the edge of the rear baffle tube. I need to flock the inside of it to see if will suppress this artifact. The telescope does not suddenly become an all-rounder, you'll just be able to draw upon a degraded, wider field of view occasionally for large objects and for centering objects. It is not the same experience as using an unvignetted refractor view. Even many Newtonians will have some vignetting due to undersized secondaries, but no one complains about it visually.

True, but the true field of view would only be 8% narrower in the 10-30mm if all the focal length and AFOV values are accurate. By the time you get to a 40° AFOV, it's feeling mighty narrow. 33° will be worse, but you're already deep into the uncomfortably narrow zone anyway.

How about the Svbony SV170 10-30mm zoom eyepiece? It's only $50+tax over here direct from Svbony's store, and £59.99 on Amazon UK and £55.99 on ebay UK. I couldn't locate a Svbony storefront in the UK. At least one person on CN likes theirs. Svbony also sells the 9-27mm zoom for about $90 to $100 +tax over here.

Recently, I measured the actual focal length of my Surplus Shed 7.2-21.5mm zoom and came up with 7.4-20.6mm, so a bit short on both ends. It's not as bad as my Celestron Regal 8-24mm zoom, though. It measures out to be 8.2-21.2mm! All I'm saying is, don't bet the farm on the 9-27mm zoom being 27mm at the long end. It probably will be pretty close to 9mm on the short end, though. Also, remember that many 2x Barlows are closer to 2.1x to 2.4x in your calculations, depending on where the eyepiece focuses relative to the Barlow's shoulder and the native power of the Barlow if the eyepiece reference plane is exactly at the shoulder. What about using a hyperwide 9mm eyepiece like the APM XWA for general viewing? You'd get plenty of dwell time at a reasonable power. I see you have some 82° eyepieces in that range already. Is this more about putting together a travel kit or trying to chase the optimum power in real time?