Louis D

Moving up from 6" to 8" won't be nearly as noticeable difference moving from 6" to 10". Try it for yourself on your 6". Create a circular mask with a 4.5" diameter opening and put it on and off over the front of your scope while observing different objects. This is the same step difference as moving from 6" to 8". Now repeat the same experiment with a 3.6" diameter mask. This will demonstrate the 6" to 10" step to you. Make sure to consider the weight and bulkiness increases in moving from 6" to 8" to 10" before any purchases. Also, each step up results in a shorter focal ratio, so each will be more and more demanding on your eyepieces in terms of edge correction. On the 10" in particular, you'll probably want to invest in a coma corrector to make the outer edges of wide field eyepieces more acceptable. If you only use 50 degree or less AFOV eyepieces, you might be fine without one.

All I can say to make exit pupil tangible is to point your scope at something bright like the sky and pull back from the eyepiece and notice how the illuminated spot shrinks with increasing magnification. If I had to guess why 2mm is the sweet spot, that's the size of most people's irises in the daytime, so that's where your vision has adapted to having the best acuity over time. As far as why tiny exit pupils are uncomfortable, it's like a pinpoint of light shining into my eyeball illuminating every floater individually in there.

I get the same feeling moving from the 17mm ES-92 to the 14mm Morpheus to the 12mm ES-92 power progression. Despite the 76 degree field, the Morpheus still feels constrictive in comparison to the two ES-92s.

The 25mm Revelation Plossl would be a good choice for not a lot of money. FLO's Sky-Watcher SP Plossls may also be GSO made. If so, they have a 10mm version. However, you may find that you'd prefer using a 20mm or 25mm with a 2x Barlow instead due to the much better eye relief. As far barlows go, since you're using a Dob, you can use a long barlow. I've compared various vintage Japanese made Barlows: Tele Vue 2x, Meade 140, and Orion Deluxe, and the Orion is just slightly sharper than the rest, though it is the longest at about 6 inches, so not a big surprise. I see it still in stock over in the UK. Just confirm it's new old stock and marked Japan made. It is actually a 2.1x Barlow like the Tele Vue. The Meade is a 2.4x Barlow.

An 8" Dob, a 72ED and 90mm Triplet APO normally. It is tricky to balance on the 72ED when viewing near zenith (it wants to turn turtle), and it can cause the Dob to sink when viewing below about 35 degrees elevation. However, the immersive views are so worth it. I have strong astigmatism in my observing eye (2 diopters), so I need to wear eyeglasses to avoid spiky stars at anything above 1mm exit pupil. Thus, my options for wide fields above 76 degrees become extremely limited. Here's photos of and through my various ~17mm eyepieces for comparison sake. The Morpheus and Delos will be fairly close in size to the AF70 and Nagler T4. It also gives you an idea of how much additional apparent and true field you get by jumping up from 60 to 70 to 82 to 92 degrees. The views always try to put the end of the rulers at the right edge, so the distance shown on the left edge corresponds to the true field of view governed by the field stop independent of edge distortion. Based on these values and the known field stop values for the Nagler from Tele Vue and ES-92 from Explore Scientific, I get 19.5mm, 22.3mm, 24.2mm, and 27.4mm moving from left to right and top to bottom. The "full view" images were taken using an ultrawide angle but lower resolution camera and then scaling the result to match the central magnification of the narrower angle but higher resolution images above them. The small edge images were taken with the higher resolution camera pointed at the edge to reduce artifacts introduced by the camera lens.

Do you raise the eyecup sleeve of the Delos to view? The ES-92 actually has slightly less usable eye relief than the Delos (17mm vs. 18mm). If you don't raise the eyecup, it would view pretty much the same.

I would pick up a 30mm APM UFF to get those wide TFOVs you desire. It views very much like a Delos or Morpheus.

Have you had the chance to compare it to the 17mm ES-92? I have the 17mm AT AF70 and Nagler T4, but prefer the ES-92. I've wondered if it would be worth it to pick up a 17.5mm Morpheus for 1.25" usage. The AT AF70 has noticeable of chromatic aberration and astigmatism in the outer 15% of the 70 degree field, so not really a viable options most of the time. Is the Morpheus free of aberrations at least out to the last 5%? The 14mm Morpheus has quite noticeable field curvature, astigmatism, and chromatic aberration in the out 10% of the field, but less than the 17mm AT AF70 and way less than the 13mm AT AF70. Still, I like the Morpheus better than my 14mm Pentax XL because of the significantly wider field.

If you like the eye relief of the Delos series, you might like to get a 12mm ES-92. It presents a just as easy to take in 92 degree AFOV without having to hunt around to see the edges. It's just there in front of your eye all at once. It's also very sharp right out to the edges. Reportedly, it's just a step or two behind the 12.5mm Nikon NAV-HW and even less behind the 13mm Ethos in overall correction. I don't have a 12mm Delos to compare it to, but it comes pretty close to the 10mm Delos in sharpness and contrast, just with a much larger AFOV.

Two different sellers. Probably newbies with deep pockets who they thought they'd get into imaging big time, but in the end found it wasn't for them, so they are dumping their little used equipment. I see this happening a lot in other hobbies as well that have large, up-front investment costs. Boats, RVs, motorcycles, ATVs, photography, video production, woodworking, metalworking, CNC, etc. Folks think, hey, I liked doing that activity that one time years ago on a shoestring budget, let's get into it big time now that I'm older and have the money to do it right. Only thing is, they're not the same people they were years earlier and their interests have markedly changed. It's one thing to properly grow into a hobby rather than jumping headlong into one from the start. Who would start being a rodeo bull rider at age 65 after having ridden a horse on vacation in their teens? Yet I've see plenty of folks drop thousands of dollars on a telescope system in their 40s and beyond after having had a department store scope in their childhood only to turn around and sell it all after 6 months to a year out of disappointment and/or boredom.

About 20 years ago, I remember Jason Ware bringing his 16" LX200 to a local star party. He used to do quite a bit of astrophotography with his. You might want to drop him a line.

For future reference, if you are only concerned with the text in the document and not the illustrations and formatting which are what are taking up the majority of the 30MB, open the document in a PDF viewer, hit ctrl-a to select everything and ctrl-c to copy everything, open a new text file somewhere on your computer using notepad (on windows) and then hit ctrl-v to paste it all into it. Save the file and tell it to lose any remaining formatting. Next, compress it into a zip file. I was able to take a 587KB PDF manual down to 27KB uncompressed and 10KB compressed with this technique. Running the original PDF file through compression decreased it to 537KB. PDF files typically contain illustrations and formatting information that won't compress much at all because it's already stored in a compressed format internally to the document. It's really only the text that can be compressed.

Two FSQs went up for sale on CN classifieds for $4800 each yesterday.

I just checked on a bunch of the low cost eyepiece kits, and they all come with one or more eyepieces at or below 8mm in focal length in a 4 element design. The eye relief on such eyepieces makes them incredibly uncomfortable to use. There's a reason Tele Vue stops their Plossl line at 8mm and discontinued their 7.4mm version. Even at 8mm, most folks report a great dislike for that eyepiece due to lack of eye relief. I also notice one kit states that their 32mm Plossl only has a 44 degree AFOV instead of the normal 50 to 52 degrees. One has to wonder where they found a 32mm Plossl with only a 44 degree AFOV? I've never seen one sold separately. The whole point of a 32mm Plossl is to maximize the TFOV available in a 1.25" barrel, and that eyepiece would fail to fulfill that most basic role. The Barlows packaged with these kits appear to be the most basic type that noticeably degrade the image. I gifted just such a Barlow to a buddy starting out, and he returned it back to me within 6 months noting how poor it was. If you really want to try a kit, I'd watch the classifieds for them since they don't hold their value very well. I'm not sure what eyepieces you have right now. However, I'd recommend the Revelation Plossls since they're made by GSO, are very good, and low cost. I have the 32mm GSO Plossl, and it is fantastic. I'd skip the 25mm Plossl as it is too close in power to the 32mm and go with the 20mm next. I think I recall you having a 15mm Plossl already, so next would be a 10mm to 12mm. I'd switch to BST Starguiders to get decent eye relief and a wider field of view in this range. The 12mm is very good while the 8mm and 5mm are excellent. With a 5/8/12/15/20/32 set, you probably wouldn't really need a barlow. As far as filters go, watch the classifieds. I've seen quite a number of 6 or 7 piece sets go for $20 or so recently. It really depends what you want. Do you want an upgrade on what you already have? Do you want to fill in gaps in power?

If you're sitting on a pile of cash, I'd wait to see what gets dumped on the used market in the next few weeks/months as folks start to run up against financial difficulties. I picked up a lot of great deals between 2008 and 2013 during the Great Recession and the period immediately following it.

Looks good. I've found the 600mm FL on my TS-Optics Photoline 90mm f/6.6 FPL53 Triplet APO to be a nice sweet spot between my 400mm class refractors and my 1200mm Dob.

I hadn't thought of getting hit, or worse, having an eyepiece jammed into your eye socket. 😵 Think about the liability issues for the manufacturer.

I'm surprised it can't deal with Dobson's hole at all. I would have expected it to issue a bunch of rapid AZ motions to eventually get a 180 degree rotation. Is it because it realizes it can't keep the object centered well enough during the contortions so it gives up entirely?

Yeah, I wouldn't open up the lens cell because trying to get all the spacings and orientations/rotations correct again could be problematic, even more so in a collimateable triplet.

Yeah, 3.5mm is really pushing things, even under steady Texas skies. I rarely go beyond using a 5mm eyepiece on most nights. I have the TV Barlow, and while it is good, it will slightly degrade the image compared to using a dedicated 3.5mm eyepiece like a Delos or Pentax XW.

I would skip the low end kits. They include lower end eyepieces and filters you probably won't use. Meade used to sell all six HD-60s in a case. I have it and can heartily recommend it. You could purchase all seven BST Starguiders from FLO and get a 20% discount on each and then buy a small case for them with pick and pluck foam. At the higher end, you could get a set of Stellarview Optimus 100 degree eyepieces with case. 😉 These are the same as the APM HDC-XWA offerings if you want to local to Europe, just without the customized case. I tend to use a variety of eyepieces from a variety of manufacturers and store them vertically in a Pelican style case.

Having done all that successfully, I'll bet your confidence level has shot way up. 😁

You'll like it. What's also really nice about them is the silky smooth zoom action. There's no stiffness in it like so many other zooms. Once the eye cup is completely removed by unscrewing it counterclockwise after the eyecup is all the way down (it retracts when rotating counterclockwise), a 37mm thread is revealed that is 6mm high with 2mm unthreaded above that. I was able to thread a 37mm step ring onto it perfectly. Thus, if you can locate a 43mm to 37mm step down ring, you should be able to attach a Dioptrx to it.

I really like my Celestron Regal and Olivon spotting scope eyepieces. Once the eye cup is screwed off, there is plenty of eye relief for eyeglasses and the top does not rotate during zooming. They vary from about 44 degrees at 24mm to 63 degrees at 8mm AFOV. The field stop is sharpest toward the central part of the zoom range and gets a bit fuzzy at either end. Edge correction is pretty decent. It's included in my eyepiece field of view images at 8mm, 12mm, and 24mm. The only tricky part is finding them since they are not sold individually anymore. I watched ebay and the classifieds to pick up mine from spotting scope owners who didn't want them but wanted to recoup some of their investment.

Avoid the 1.25" WO diagonal. It vignettes widest field eyepieces because of thick ring in the eyepiece receiver. I've got one and can confirm this. I wouldn't have bought it if I had known about this issue ahead of time. As far as 2" diagonals go, I like the GSO dielectric so much that I have 3 versions of it. One is GSO, one is TPO, and one is ScopeStuff branded. One is quartz, the rest are regular glass. I can't say the quartz is any better, but it was the same price as the others used (about $70 each). They're branded Revelation in the UK. I have never been disappointed by any GSO gear. Their 2" ED 2x barlow is excellent, their 32mm Plossl is excellent, and their coma corrector is excellent.