Louis D

Is eye relief an issue for you since you chose long eye relief eyepieces at 24mm and presumably 17.5mm? The 2.6 GPC (or simply a high quality Barlow element in my experience) would work great with the 24mm and 17.5mm eyepieces to yield higher powers. I would look into a pair of zoom eyepieces because swapping eyepiece pairs is a royal pain, especially at high powers; although I suspect you're using a tracking mount.

How do you deal with the fact that the BHZ top rotates as it is zoomed? Doesn't this require reorienting the Dioptrx after each zoom? The rotating top of the BHZ is what keeps it from being used in binoviewers with batwing eyeguards.

The 12mm is the best corrected to the edge of those three. I would add the 5mm and/or 8mm next. I haven't looked for ghosting in my Paradigm/BST samples. I suppose I'll have to explicitly look for it sometime.

Why the photographic tripod requirement? A compact travel Dobsonian is it's own base:

I unscrewed the chrome barrel from my 18mm Paradigm/BST, and it does indeed have at least one lens at the very top of it. I didn't try to ascertain whether it was a single lens or a doublet.

Have you tried it during the daytime on a distant target to see if it focuses under those conditions?

I'm thinking a thin layer of silicone lube wiped on with a cloth would work well without ever drying out.

Since your achros are around f/10, you might give the Svbony 68° UWA a try for under $30 a try. They're pretty good in longer focal length scopes. They are sold under other names as well, sometimes advertising 66° FOV.

On CN, Markus reports UO has started production and first shipment to his home is expected in October.

Just checked mine, and yes it does have a lens in the chrome barrel. It's up there a ways compared to the shorter focal lengths, but it's definitely with the barrel. Thanks for the heads up about the 18mm. I knew the 25mm didn't have a Smyth lens in the barrel, but never realized that the 18mm didn't either. In fact, both have their field stop below the field lens, so they're actually positive-only designs. I compared them to the Meade HD-60 18mm and 25mm which both appear to have lenses in the barrel. That's probably why they have better correction at the edge than the BST Starguiders/AT Paradigms.

Glad it worked well for you. Enjoy the summer/early fall skies, there's lots to see up there right now. I just find it amusing that Brits call rain barrels water butts. Pork butt, sure; but water butt? Apparently, the term "butt load", which Americans still use, derives from this older meaning of the word, but we have long since forgotten the origin of the term.

However, the APM 24mm UFF has at least as much true field as either the 24mm Panoptic or ES-68 due to much lower edge distortion. I've measured the field stop at 27.5mm, though it tends to fade out a bit due to some vignetting. Eye relief. You can see the entire field of the APM 24mm UFF while wearing eyeglasses. You won't be able to do the same with the 24mm ES-68. Correction wise, they're probably similar.

At least not as long as they stay in a 1.25" barrel. Were they to switch to a 2" barrel like the 17mm and 22mm NT4s, 14mm and 20mm Orion LHDs, and 22mm AT AF70/Omegon Redline SW, etc., then they probably could go with longer focal lengths.

For me, the deal breaker is no altitude clutch to allow heavy eyepiece changes. Once balanced and the axis tensions are backed off, I don't generally use the slo-mo controls on my DSV-2B mount while tracking. It's so much easier to just use a light, fingertip touch on the handle to track than trying to alternately mess with two slo-mo controls. I took a pass on the DM-4 and DM-6 mounts because they have no altitude clutches. I was with a fellow observer using a DM-6 mounted 140mm refractor at a star party and watched his contortions trying to hold two large eyepieces while trying to prevent the scope from nose diving as he swapped them. I was appalled at how un-ergonomic it was. It tracks fine without slo-mo controls once the eyepiece is changed, though. My DSV-1 mount is fine for short telescopes and light eyepieces, but I wanted to be able to mount larger scopes and heavier eyepieces, so I bought the DSV-2B for them. I wouldn't go much past a 100mm refractor with it. I'd probably get the DSV-3 at that point. I guess my point is the lack of an altitude clutch on the NOH CT-20 is a deal breaker for me.

I picked up my used copy from someone who couldn't get on with a pair of them in his BV. I don't know if it was due to an IPD issue, a nose space issue between them, or something else entirely like weight or ability to merge images. Just temper your expectations for the 24mm UFF pair in a BV.

For my two Morpheus: 14mm: 77° by projection, 78° photographically 9mm: 78° by projection, 79° photographically And before anyone suggests a systemic error between the two, the two measures match for many of my eyepieces, and the first is sometimes larger than the second. They are generally within 1° of each other. Eyepieces without a physical field stop are problematic for both methods because it's a judgment call to define where the usable field ends as it fades to black either in the projected or photographed image.

I measured 16mm of usable eye relief for the 30mm APM UFF, although it feels more like 17mm in use. Both work comfortably with eyeglasses. I think that's why the 24mm's eye lens was recessed so much, so it would have a similar feel to the 30mm and many other eyepieces with about 17mm of usable eye relief. Too much eye relief can be a bad thing even with eyeglasses.

Nor do they attach to all eyepieces. There are various hacks out there (check CN in particular) to use them with certain Pentax, ES, and APM eyepieces.

I would never use an expensive pair of varifocals at the eyepiece. There's too high of a risk of them being damaged. That, and they probably have lots of microscratches that cause fine stars to twinkle as your head moves through the exit pupil. I bought a pair of distance only eyeglasses with the lowest dispersion lens I could get so my astigmatism is corrected for use at the eyepiece. I bought them through EyeBuyDirect for about $20. They stay in a case in my astro toolbox and only get used for astronomy, so they don't build up daily microscratches. When I need to read something up close, I simply look under my eyeglasses because my old eyes are fixed focus at 8 inches.

That's the design eye relief. The eye lens is recessed so much that it ends up having 17mm of usable eye relief. You will need to touch the folded down eye cup to see the field of view while wearing eyeglasses.

Not so much aperture as large exit pupil. Yes, that will mean lower magnification with smaller aperture scopes, but that can be a good thing for large objects like the Veil nebula. If I had started with my Lumicon UHC, I probably would have written off all nebula filters as "Meh". Some improvement, but not a dramatic improvement in the view. The OIII is a "Wow" filter with what it can bring out. Invisible nebula like the Veil stand out as etched on the sky. Remove it, and the Veil disappears. Is the OIII filter right for all emission nebula? Certainly not. However, more often than not, it offers a very noticeable improvement in the view.

Yes, it can be a useful way to stretch your dollars starting out. Just be aware of how long things get with a Powermate, Paracorr, and a 100 degree eyepiece all in the focuser at the same time: Focuser flex could become an issue. Although as @John has pointed out, they can come in handy for other uses:

I use a cheshire/sight tube to get the secondary square under the focuser. I use a laser to get the secondary on the center of the primary. I use a Rigel Aline to get the primary lined up with the rest of the system.

Agreed. Also, there's a lot of wiggle room in the 11mm to 16mm space as to what is the best workhorse focal length. It depends on the focal length of the scope, the apparent field of view of the eyepiece, and observer preferences. For instance, I started out with a 14mm Pentax XL at 65°, but later found that the 12mm ES-92 covers more sky at a higher magnification without shrinking the exit pupil too much in the process.

Written by people who haven't spent a good chunk of their lives out under the stars, I suspect. I tend to leave mine in the focuser the entire night when I want to use all of my eyepieces at double their normal magnification, which isn't very often. 25x to 50x is good for very large open star clusters, solar system conjunctions, typical solar observing (with safe solar filter) sweeping rich star fields, and detecting comets. 50x to 100x is good for large open star clusters, emission nebula, the whole moon at once, and large galaxies from dark sites. 100x to 150x is good for small open star clusters, planets on nights of average seeing, smaller galaxies from dark sites, viewing the moon in large swaths, and splitting many double star systems. 150x to 200x is good for planets on nights of above average seeing, planetary nebula, lunar details, starting to resolve globular clusters, and splitting tighter double stars. 200x+ is good for planets on nights of exceptional seeing, bright planetary nebula details, challenging lunar details, interacting galaxies from dark sites, fully resolving globular clusters, and splitting the tightest double stars. I'm sure I missed someone's favorite type of observing in there. That, and folks will argue about what magnification works best for each. It's nice to have an assortment of eyepieces to try out to match the seeing conditions with the object at hand. OIII only pass the two oxygen emission lines while UHC filters add one or both hydrogen emission lines. As a result, the OIII filter has a narrower passband and a higher rejection of light pollution. However, some emission nebula just don't emit much in the oxygen lines, so the UHC or even an Hß filter comes into play. You don't use them together. It's either one or the other. The OIII is a subset of the UHC. The OIII and Hß are mutually exclusive. A lot of folks like the Baader Contrast Booster on planets and other objects to make it easier to pick out low contrast details, but I've not tried one personally. I've had some luck with an 80a filter on Jupiter to bring out the Great Red Spot better. Probably not. They're heavy and fat. You might not be able to get two of them close enough together for your IPD. That, and your nose or at least its bridge between your eyes might not fit between the eyepieces, either. Most folks use smaller, lighter weight eyepieces in their BVs. Adapted microscope eyepieces can even work quite well I've found. Also, most folks tend to use lower powered eyepieces with BVs because it's easier to merge their images. Higher powered eyepieces tend to reveal any slight miscollimation in the BV. You can always boost the power by adding a Barlow element ahead of the BV. They also help you to reach focus in Dobs which don't usually have enough in-focus for BVs natively (about 100mm required).