Don Pensack

If you look at Ernest Maratovich's tests of many eyepieces, you'll see that many many eyepieces yield edge of field apparent stellar sizes in excess of 10'. http://astro-talks.ru/forum/viewtopic.php?f=32&t=1483#p41976 start with the 4th post on that thread.

And if the lower circle was a lot smaller than the upper circle, wouldn't the spot sizes be larger instead of smaller? That's one reason I think they meant milliradians in the bottom row, not microradians.

That would make the circle 0.01375', or 0.825", and the spot size a small fraction of that I think they made an error. That would make the star image essentially diffraction limited near the edge of the field. I've seen that in several eyepieces at f/10, but none with a 4 element construction.

I constantly monitor that when I am in the field. My last time out, I used 8 of 13. The time before that, I used 11 of 13. The time before that, I used 12 of 13. I typically will look at objects from 10" wide to 1.3° wide, which requires vastly different magnifications (60-500x) and eyepieces (30-3.7mm) It's hard to have only a few. I could see having 9, but I'd be hard pressed to decide which eyepiece to unload. I'm looking at 2 right now (4.7mm and 4.8mm), one of which can go. But I need to spend some time with both to decide which, and the nights are so short, now.

Let's see: 17.5mm Baader Morpheus 11mm TeleVue Apollo 9mm Baader Morpheus 7mm APM XWA 6mm TeleVue Ethos But there are others I'd miss. 5 is a harsh number when covering a 60-500x range, but I could live with 8.

Takahashi identifies those circles as 4 milliradians, which translates to 13.75' in apparent size. That is not a great lateral sharpness, but is typical for a well-corrected 4-element Plössl. They admit that the edge deteriorates, and given the specs, I'm sure it does. But they also don't identify the f/ratio that yields those spot diagrams, so the actual performance of the eyepieces will depend on that factor.

This would push the eyepiece back so far he's need 2" of in-travel. He might have that 2", looking at the picture. But: The best solutions are: --Parfocalizing ring on the eyepiece so the eyepiece stops before it is fully inserted. --2" barrel extender on the eyepiece --2" barrel extender on the diagonal nosepiece. Barrel extenders are inexpensive and come in lengths of 5mm to 50mm.

Celestron X-Cel 2.3mm

LOL. I'll correct the wording. Thanks.

Perhaps you haven't used hundreds of different eyepieces, so I'll repeat what I often say: There are differences in eyepieces, and I certainly prefer some to others. But, in 60 years of observing with 31 different scopes, never have I encountered a non-defective eyepiece (I've encountered only 3 defects) that did not allow me to see everything the aperture was capable of seeing when the Seeing conditions were perfect. I've done scores of eyepiece comparisons, and a few have had sharper edge focus, or perfectly flat fields, or better correction of chromatic aberration, or superb contrast, or better behaved exit pupils, etc., etc. But, on axis, in a cooled and well-collimated scope, the difference in image quality among eyepieces is pretty small--a fly on the rump of a horse. Take a look at the on-axis measurements of Ernest Maratovich in Russia. I think of the few hundred tested, maybe 1 was less than a perfect image on axis. We eyepiece aficionados tend to make extremely minuscule differences into a good/bad dichotomy and tend to forget how incredibly important the atmosphere is.

I think it is because many people just accumulate stuff in their lives and never unclutter. The neighbors who moved to assisted living had their son clean out the house and it took two large moving vans to haul the stuff away that didn't sell. They had everything they had ever gotten in their 60 year marriage in the house. Eek! Every few years, my wife and I go through all our possessions and unload unused clothes to the services catering to the poor. Mostly, we just give it away to libraries, used book stores, thrift stores, etc. I have too many eyepieces, but they were collected over years and I have yet to decide whether or not to unload the extras. I have noticed that every time I go out to the field, I use every single eyepiece or maybe just a couple fewer. I use glasses down to 9mm, and, below 9mm, I have 2 compatible with glasses (in case I want to keep my glasses on), and 4 not compatible with glasses (much wider apparent fields) for when I want to take my glasses off. Some observers have special eyepieces used only for planet observing. Some observers prefer half-millimeter spacing on high power eyepieces. Some observers prefer close spacings at low powers because they spend a lot of time there. For a single scope owner, it is difficult to imagine that more than 20 eyepieces would/could ever be used, but what about the owners of a half dozen scopes? Different focal lengths of telescopes need different focal lengths of eyepieces. And don't forget the binoviewer/binoscope users with 2 of everything used in those scopes. Still, your point is valid. If you have scores of eyepieces, you most assuredly have duplicates.

What is the best planetary eyepiece? The one in the focuser when seeing is perfect.

I think it might be consensus that Takahashi doesn't actually make eyepieces, but sub-contracts them to an eyepiece maker. Whether or not they own or partially own said company or companies would be pure speculation unless you are a Takahashi insider. These new eyepieces say "Takahashi" on the outside, not Starbase. Starbase eyepieces are made by Dai-ichi Kogaku. Whether these new ones will be made there is unknown. Takahashi is just realizing that the owners of Takahashi scopes are either astrophotographers or lunar/planetary/double star observers. Hence the 48°, and a disinterest in glasses-friendly eyepieces. Their 90° eyepieces lasted only a minute, though there are still a few of them out there in dealerships.

O-rings are easy to replace. Lenses are easy to clean. Store in a case to prevent the aluminum from wearing more.

The planet/seeing issue is why a constant magnification increase makes more sense than a constant % change. Pentax and Baader use constant % changes and this results in too-large magnification changes at high powers and too-small magnification changes at low power. Example: 8" SCT with 2032mm focal length: Constant magnification: 50/100/150/200/250/300x. By % change it is +100%, +50%, +33.3%, +25%, +20%. Constant % change (using 40%, a common increase): 50/70/98/137/192/269/376x, or increases of 20x, 28x, 39x, 55x, 77x, 107x If bumping up against the seeing conditions, the first makes more sense than the latter. One exception, however, could be a person whose interest is mostly deep sky with a side interest in planets. In my 12.5", for example, I keep magnification increases modest until 300x, and when the seeing is good enough that 300x is sharp and steady, jumping to 400x and 500x above that seems fine for the objects that are typically viewed at such high powers. I don't feel the need for small magnification changes at low powers or the highest powers, only in the middle range where I spend most of my observing time. Hence the "U" shaped magnification regime, where magnifications slowly increase or decrease on either side of a most-used magnification and get larger the farther the choice is away from that magnification. At low powers, large jumps in magnification are required to make an appreciable difference in the views. At high powers, if a certain magnification isn't enough, a large jump will get you to the power you need. This protocol works fine as long as you observe at a site with good seeing, but wouldn't work for a planet observer in mediocre seeing. There, the best idea seems to be to creep up on the maximum by having higher powers closer together.

Not worth it for such a slight difference. It would be worth it if moving from the Radian to, say, an APM 7mm XWA 100° eyepiece (which is also 1.25"), where the field would be 2.78x as large in area and 1.67x as wide. But, if the intention is to have small, lightweight, eyepieces in 1.25", and you use glasses at the eyepiece, then stick with what you have. Another, wider, small, lightweight, 1.25" eyepiece would be the 7mm TeleVue Nagler Type 6. In that case 1.87x as much area of true field and 1.37x as wide. Like the XWA, not glasses-compatible.

Yes, read what Tele Vue has to say. And clean your eyepieces more often--don't let them get that dirty. Alkaline dust on the lens, in combination with dew, can etch the coatings. Never use a lens pen. Like threaded-onto-the-eyepiece solar filters, they should be permanently discontinued by everyone. They scratch the eyepiece lenses all too easily.

The Omni Barlow changed from its original, and the lens is now in a housing ever-so-slightly smaller than 1.25". That might mean they changed the threads on the lens, so be sure to ask if it still threads directly to a 1.25" eyepiece. FLO sells others that do, in case the Celestron is no longer usable that way. Of course you could still use it under the eyepiece in its own tube (2x) or in front of the diagonal in its own tube (3x) if you didn't want the other magnifications possible. Used in front of the diagonal, it usually requires a lot of infocus. It depends on your scope if that is possible or not.

F/11.1. Maximum focal length 78mm eyepiece (doesn't exist). Minimum focal length eyepiece 5.5mm The vast majority of your observing will be in the 55mm to 11mm range, with the sharpest views with eyepieces of 22-33mm. But, a decent 90mm does pretty well at 100x, or a 9mm eyepiece. once you get into the 100-180x range, though, seeing will determine how high you can go. If well corrected, an f/11.1 doublet in that aperture will not suffer from chromatic aberration, so seeing will be the main problem above 100x. 90mm is aperture-limited when looking at higher powers, but Jupiter and Saturn look fine at around 150x (6mm eyepiece), so I don't think there is necessarily anything wrong with having that focal length, but buying a 6mm eyepiece that will stay in the case most nights is not economical. So I advise getting a 2X Barlow lens, which would turn the 32mm into a 16mm and the 12mm into a 6mm. And if it is the type of Barlow (like a Celestron Omni or something like it), that the lens detaches from the Barlow and attaches to the eyepiece, that that Barlow could give you 1.5x with the Barlow's lens threaded directly on the eyepieces (resulting in 21mm and 8mm focal lengths) 2x under the eyepiece in the Barlow's original configuration (resulting in 16mm and 6mm focal lengths) 3x in front of the star diagonal (resulting in 10.7mm and 4mm focal lengths). Because a simple 2X Barlow lens can effectively double or triple your entire eyepiece collection, it is VERY cost-effective. And if your star diagonal is threaded for filters on its inserted nosepiece, the Barlow's lens can also be threaded there for roughly a 2.5x magnification, quadrupling your eyepiece collection. You could have 1x, 1.5x, 2x, 2.5x, and 3x, or 10 magnifications with just 2 eyepieces. For a variety of reasons, you might want to get separate eyepieces at discrete magnifications at some point, but the Barlow lens should give you what you want. FLO has one for only £27 https://www.firstlightoptics.com/barlow-eyepieces.html

APM UFF 30mm = Altair Astro UFF 30mm = Meade UHD 30mm = Celestron Ultima Edge 30mm = Sky Rover Ultra Flat 30mm = StellaLyra Ultra Flat 30mm = Tecnosky Ultra Flat Field 30mm. All are the same eyepiece internally. APM XWA 20mm = Astrotech 20mm XWA = Stellarvue Optimus 20mm = Antares XWA 20mm = Sky Rover XWA 20mm = Tecnosky XWA 20mm = Telescope Service XWA 20mm All are the same eyepiece internally. There are lots of private label incarnations of the same eyepieces these days.

I can't say. I did use them briefly in my 102mm f/7 triplet refractor and didn't notice field curvature. The 16.5mm, in specific, had a very flat field. I used them in the daylight. I wanted to determine if I could use glasses. But, that was only a few seconds to see if I could use glasses with them, and most of their usage was in my 12.5" reflector with Paracorr. I could use glasses with them if I pushed my glasses hard against the eyecup and my eyelashes were brushing the back of the eyeglass lens. Not comfortable for more than a few seconds. With a comfortable pressure against the eyecup, I could only see maybe 70° of field or a hair more. I think one would say they are glasses compatible only for those glasses wearers who have a near-zero distance from eye to glasses lens and thin lenses in the glasses, which probably rules out at least 80% or more of glasses wearers. The eyepieces have 20mm of eye relief from the glass, but only 12mm of eye relief from the rubber eyecup.

Then you will find them both comfortable. Enjoy.

I reviewed both of them: https://www.cloudynights.com/topic/849945-new-85°-pentax-eyepieces/?p=12369694 https://www.cloudynights.com/topic/849945-new-85°-pentax-eyepieces/?p=12369699 Bottom line: The 16.5mm is better than the 23mm, 85-90% of glasses wearers will not be able to see the entire field when wearing glasses (you need a very very close eyeglass-to-eye "vertex" distance to use only 12mm of effective eye relief from the rubber up. The 70° XWs have about 3mm more effective eye relief than the 85s.). They are heavier than the 22mm TeleVue Nagler, and I'm not sure about the transmission %--they seemed darker than other eyepieces at/near the same focal lengths. I use a Paracorr in my dob, and the 23mm was noticeably vignetted. Is that inherent in the 23mm, or an interaction with the Paracorr? I don't know. The 22mm Nagler does not, but that does not prove the 23mm eyepiece is at fault. I liked the 16.5mm enough it might be in my collection right now had the eye relief been sufficient for glasses. It is compatible with a DioptRx, however, though eye relief would be VERY tight with DioptRx added.

Spherical, or SPH, refers to distance correction. This can be adjusted using your focuser. Cylinder, or CYL is the astigmatism specification on a prescription. This is what a DioptRx corrects.

Is the 5mm Nagler DioptRx-compatible? Yes, with the TeleVue adapter that allows it. Do I recommend the DioptRx on the 5mm? No, I don't. The eyepiece has only 12mm of eye relief before the DioptRx is added and it reduces the eye relief to about eyelash length or less. Either you pull your eye back every time you blink, or you get eyelash oils on the DioptRx every time. Your scope is f/7. A 5mm yields a 0.7mm exit pupil in that scope. For you to need glasses at that focal length of eyepiece means your astigmatism needs to be 3.5 diopters or worse. If you have that much astigmatism, you do need the correction. But if you don't, the eyepiece would be usable without glasses (you simply refocus the scope for refractive error, either myopia or hyperopia or presbyopia). The alternative, if you do have that much astigmatism, is to get an eyepiece that is usable with glasses on, like the 4.5mm Baader Morpheus, 5mm Baader Hyperion, 5mm Pentax XW, etc.