Louis D

Let's say you want to stop at 0.5mm exit pupil, that would be 130mm/260x or a 650mm/260x=2.5mm eyepiece. This power would mostly be useful on the moon and for double star splitting. For planets, I would back off to no smaller than a 1mm exit pupil with a 5mm eyepiece to maintain decent, though not exceptional, contrast. This equates to 130x. The 5mm BST Starguider is a very good performer for not a not of money. I'd start with it and see how you like it.

I found them in stock at multiple places in the US (Agena, OPT, Amazon, High Point, possibly others). How badly do you want one?

1. Hopefully, you at least opened the window. Viewing through windowpanes is a recipe for blurriness at high powers. They are going to be far from planar at the wavelengths of visible light causing distortion like a bad lens. 2. Hopefully, the inside and outside temperatures were close. Otherwise, you're going to get thermal gradients as air rushes through the window to equilibrate the temperature differential. Those thermal gradients will act like lenses distorting your view. 3. In summary, if you're going to view from inside through a window, open it wide open and allow the temperature inside to reach the outside temperature before observing. Perhaps running a box fan in the window temporarily would hasten this process.

I'm assuming you've already read this comparo, but it case you haven't: Other than it, I don't know of any detailed shootouts across Planetary brands.

If you've got both, give it a try sometime and let us know. I'll try the GSO ED alone sometime with the ES-92s to see what happens. I also have an Orion Deluxe 2" 2x (Japan) that's 6" long I could try. I could even thread the GSO ED optical nose piece onto the end of the ES-92s for grins.

The full moon is no brighter than f/16 at 1/125s at ISO 100. Let's say you're shooting with an f/5.6 telescope. That would be 3 stops faster which would necessitate either ISO 12.5 or 1/1000s shutter speed, or some combination of the two. Perhaps ISO 50 and 1/500s. It depends on the ISO settings available in your DSLR. High shutter speeds are your friend in this case because they will mask mount vibrations and reduce atmospheric blurring. In fact, some astrophotographers will take hundreds to thousands of video frames, select the best, and stack them with specialized post processing software to create ultra sharp images. To get the earthshine illuminated half will require a vastly slower shutter speed and/or higher ISO. You would then need to composite the two images (dark and bright parts) in post processing.

The APM XWA is available in 9mm and most recently, 7mm, focal lengths. Yes, not exactly 8mm. Have you tried the 17mm ES-92 in a telecentric magnifier? I have with my 2" GSO ED 2x Barlow and TV PBI, and it works really well, as does the 12mm ES-92. It does make for a very long and heavy optical stack, though. I'd recommend it only for Dobs with stout focusers.

A Barlow will increase magnification and exposure time. It will also spread out the image circle, decreasing vignetting relative to no Barlow, assuming you use a 2" Barlow. I'm not sure about vignetting with a 1.25" Barlow and a DSLR. It would depend on the sensor size. I'm not sure why you would want to put a moon filter in front of your DSLR. Just use a higher shutter speed or lower ISO instead.

Not clear if it has been discontinued in the US.

The 17mm ES-92 is, if anything, even nicer than the 12mm in that it is slightly sharper to the edge and slighter flatter of field. It also has a slightly easier exit pupil to hold as @John reports above. It is definitely one of my favorite eyepieces to use every time I observe mid-sized objects.

@Don Pensack reported on CN that ES told him in 2016, and I quote: "Learned today there will be an 8.8mm , a 6.5mm, and an, as of yet, unspecified focal length in the series appearing in 2017." So don't hold your breath waiting for them. 😆

I don't have the 31mm NT5, but I do have the 30mm ES-82. By my scale, I get the following weights: 30mm ES-82 (original mushroom top) : 973g (decloaked), 1369g (with cloaking eye cup) 17mm ES-92 : 1153g 12mm ES-92 : 1011g Tele Vue eyepiece specifications page lists the 31mm NT5 at 998g So, the 12mm ES-92 is just about identical in weight to the 31mm NT5 and 142g lighter than the 17mm ES-92. The 31mm NT5 is just about the same weight as the decloaked 30mm ES-82. The only other eyepiece that I use which weighs over 900g is the 35mm Baader Scopos Extreme at 1072g. I have a feeling its weight and bulk doomed it despite really excellent performance for its price. I ended up buying an alt-az mount with axis locks (DSV-2B) to facilitate heavy eyepieces changes. At a star party I attended, even the DM-6 struggled during heavy eyepiece changes without axis locks. The owner had to keep a finger on the diagonal during changes to keep it from nosediving.

It's a pretty sweet eyepiece, isn't it? I'm just hoping for a 22mm to 24mm version to replace my 22mm NT4 someday.

Right, astigmatism on the line isn't intrusive. It's there if you defocus stars, but doesn't scream out at you in focus. There's the 24mm ES-82 as you suggest, the 22mm Nagler T4, 21mm Ethos, 20mm ES-100, 20mm APM XWA HDC, 21mm Meade MWA, 23mm Celestron Luminos, 25mm ES-100 (close). That's just off the top of my head. I'm sure I'm missing some contenders.

And that's why the Barlow stays in the focuser once it's in there for me. I don't do this very often, but it can be fun to use lower lower eyepieces at higher power. Examples would be the 30mm ES-82, 22mm NT4, and 17mm/12mm ES-92s. Of course, don't try this without using a telecentric magnifier. I use a TV PBI in a 2" GSO ED 2x Barlow to make a poor man's Powermate.

Something around 12mm, give or take a few millimeters, would probably be ideal. It's going to come down to your preferences for apparent field of view, eye relief, weight/size, 2" vs. 1.25", budget, etc. I really like my 10mm Delos and 12mm ES-92 in this range. There are so many choices, though. Perhaps you could start with your budget and barrel size preferences?

I ordered an eyepiece from Germany to the US a few years back, and the outer box was smashed in, but the eyepiece box inside it was fine. However, that retailer didn't bother to put packing peanuts or anything else around the inner box, so it was free to shift all over. Ironically, it may have actually helped it because it was free to move to the other side when one side was smashed in.

Clearly, when production was moved to China between the NLV and SLV lines, the optical designs were not updated, but the marketing and eyepiece labeling groups got lazy (I'm being generous here to not call them dishonest). It's not as bad as Meade calling their MWA line 100 degrees when they're way short of that. Your very own Winston Churchill coined the term "terminological inexactitude" back in 1906 which sort of applies here.

I've been using a 5.2mm Pentax XL for 20+ years. It's very comfortable to use with eyeglasses, is absolutely sharp to the edge, and has very good contrast and transmission. It works very well to resolve globular clusters, for instance. The image of them is unchanged as they drift across the FOV. I've had no incentive to replace it. The 4.5mm HD-60 and 5mm Paradigm (Starguider) are a bit less sharp and contrasty, but good for those on a budget. It comes down to quality of lens polish and coatings as well as internal stray light control.

Sounds like its time for a 5-way zoom shootout. 😁 I'm especially interested in usable eye relief characteristics, mechanism smoothness, and sharpness/contrast center to edge across the focal length range.

You've probably already seen this chart on Tele Vue's Dioptrx webpage; but in case you haven't, I've found it to be pretty accurate about when astigmatism becomes intrusive: That's not to say it's undetectable right on the line between regions. It's just unobtrusive enough there for most folks that the benefits of shorter eye relief, planetary specific eyepieces outweighs it.

I'll believe Don when he says it's, but why would you need a Dioptrx at such small exit pupils? How much astigmatism are you dealing with in your observing eye? I have 2.0 diopters, and below a 1mm exit pupil, it isn't much of an issue. I still prefer long eye relief at shorter focal lengths just for viewing comfort and consistency across my eyepieces, but it's not essential as it is at low powers.

I'm an engineer who has to regularly write up detailed processes on how to perform complex tasks, so I can't help it.

Your title caught my eye. I'm trying to picture a Neutronian telescope. I gather it would be incredibly dense like a neutron star. The intense gravity could probably bend light waves alone, dispensing with the need for lenses or mirrors. However, getting close enough to view anything would be fatal as it would crush you in an instant. It would also tend to crash through the Earth's crust and mantle and lodge itself at the Earth's core. That alone would make delivery logistics a nightmare. As others have said, I would probably err toward the refractor at this price point. If you want a Newtonian, I would steer you toward the AWB OneSky Reflector Telescope since you're in the US. It's the same as the Sky-Watcher Heritage-130P Flextube in the rest of the world. It has been universally praised as a good starter scope. A good solid tube Newtonian option is the Orion StarBlast 4.5 Astro Reflector Telescope. It's a bit faster, so it's more demanding on eyepieces and collimation.

Not much of an issue on the moon because it is an extended object of considerable size and high contrast. It is an issue with low contrast planetary features for me. I can't recall it being an issue for double stars since they tend to be fairly high in contrast. It might be an issue if you're trying to detect a faint companion next to a bright star.