Don Pensack

You will probably need an optical corrector (GPC) to come to focus. If you do, don't get the one from William Optics. I found it added chromatic and spherical aberration Big Time. There are several other brands that would throw the focal plane far enough back that don't add appreciable aberrations.

It's a little more complicated than that. All positive eyepieces can have a field stop the same diameter as the inside of the barrel, maybe a tad smaller to allow for a field stop. But negative positive designs max out with a field stop that is smaller than the inside diameter of the barrel because the field lens expands the image after passage through the lens. As a result, an all-positive 2" eyepiece can have a field stop of 46-46.5mm, whereas a negative-positive design maxes out at 42-43mm. In a 1.25" eyepiece, field stops of 27-27.5mm are common in all-positive designs, but 24.5mm seems to be the maximum for a negative-positive design. It is the reason why an APM UFF 24mm has a 27.5-27.6mm field stop and is 1.25", while a 20mm T5 Nagler had a 27.4mm field stop and was a 2". Louis points out that a designer can go too far in shoehorning a too-large field stop into a smaller barrel. The Meade series 5000 18mm UWA went from a 1.25" to a 2" diameter to reduce vignetting and it only had a 24.3mm field stop.

That is astigmatism, and it is inherent in the eyepiece. The 31mm and 36mm Hyperions are best used at f/10 or longer focal ratios, and, even then, display residual astigmatism. There are better-corrected eyepieces at those focal lengths.

Supposedly, per the rumor mill, they are the same eyepiece in different housings. Whether anyone has verified that, I can't say.

It may or may not be better than the 21mm. It depends. If your scope is f/4-f/6 it would be an improvment. If your scope is >f/8, probably not, since the 21mm and 17mm are the best in the Hyperion series. However, shop for price. The Celestron is unlikely to be the least expensive label. The same eyepiece is available in several labels: Altair Astro UltraFlat (green) APM Ultra Flat Field Celestron Ultima Edge Meade Series 5000 UHD Orion Ultra Flat Field Sky Rover Ultra Flat Field Stella Lyra (FLO) Ultra Flat Tecnosky UltraFlatField

Rother Valley Optics may have them. All the above are made by Barsta. I have not researched whether there are coatings or internal baffle differences between them. I also note there have been running changes on lower baffles and retaining rings over time.

You might also try the BST Planetary eyepieces (they are identified by a 58° rating). They are sold under at least 8 brand names. And they all have roll-up eyecups. And they come in 6mm, 7mm, 9mm sizes. Here is one of those brands: https://www.firstlightoptics.com/skywatcher-eyepieces/skywatcher-uwa-planetary-eyepieces.html

I compared the 17.3mm Delos to the 17.5mm Morpheus and kept the Morpheus, though the fields are identical in size. There was just something about the 17.5m I liked a bit more. I don't remember now just exactly why. But, the 17.3 Delos as a very nice eyepiece.

They had to design the Paracorr so that eyepieces could get closer to the lenses than in the Paracorr I. And the adapter had to support the eyepieces that had a combination 1.25" and 2" skirt which needed a longer support for the 1.25" barrel that goes up inside the 2" skirt. So a flat top adapter would require redesigning their dual-sized eyepieces. A Hi-Hat style adapter is taller (some people do need a taller adapter), AND is compatible with 1.25" eyepieces with 2" skirts. I would emphasize the In-Travel adapter was only designed to parfocalize the 17.3mm and 14mm Delos with the other sizes. That adapter is not necessary to use the 17.3mm and 14mm in the Paracorr. Only one 1.25" adapter works with all TeleVue (and nearly all other brands)--it's the one that comes with the Paracorr. As a company that offers almost 50 different eyepieces, TeleVue is also under no obligation to design their equipment to work with everyone else's eyepieces. Yet, by and large, their equipment does.

That looks a lot like the color black anodizing ends up looking like when faded by the sun.

There were multiple versions of the S4000 "Super Plössls". The exact dates are a bit confused because there was store stock later than Meade actually brought them into the US market or the European market. Version 1 was a smooth side, no rubber eyecup, 5 element, made in Japan, mustard color lettering. Production seemed to end ~1990 +/-. Nicknamed the "pseudo-Masuyama" version. Version 2 had a rubber eyecup, 5 element, made in Japan, mustard color lettering. Production definitely ended in 1994 for these. Version 3 had a rubber eyecup, made in Japan, 4 element, mustard color lettering. There may have only been one production batch ~1994 Version 4 had a rubber eyecup, made in Taiwan, 4 element, mustard color lettering. It appears there may have been only one production batch of these, as they are rare. Version 5 had a rubber eyecup, made in China, 4 element, mustard color lettering. Version 6, 7, 8, and no one knows how many more, had a rubber eyecup, 4 element, made in China, white lettering. To add confusion to the mix, Meade, apparently, with their last production, went back to mustard color lettering. How many years ago that was I can't find the answer to. You cannot trust that is what you will get, though, because many retailers have very old pictures on their sites and may have stock of the white lettering versions. One industry person mentioned several years ago that Meade had had at least 6 different manufacturers make these, and possibly more.

Louis makes a point. I was unimpressed with the quality of the star images in the APM 30mm Ultra Flat Field when I first reviewed one several years ago. A couple years later, I decided to try wearing my glasses at the eyepiece because it was obvious I needed them to see naked eye stars as points instead of little stick men. Eureka! Tiny pinpoint star images from edge to edge in the 30mm. Why I hadn't realized it was in my eye was because the star images in the center of the field were no worse than the 36mm or 31mm Baader Hyperions and I just figured it was the same level of eyepiece quality as the Hyperions. Nope. I went back to wearing glasses and tried the two Hyperions again--still bad. But the 30mm APM became world class.

Louis, There is method to their madness. The 31mm Nagler, 21mm Ethos, 17mm Ethos, 17.3 Delos and 14mm Delos all use setting A, with the Delos both using the 10.5mm tall adapter. There was no setting that far in for those eyepieces in the Type 1 Paracorr. Setting B works for the 22mm Nagler and the 6mm and 8mm Ethos (the Ethos are used as 1.25" eyepieces). A Hi-hat style adapter was necessary for safety on the 6mm and 8mm Ethos--a flat top is less safe--but the 16.5mm tall Hi-Hat adapter wouldn't have worked for the 6mm and 8mm Ethos or the 2 longer Delos eyepieces. The Ethos 6 and 8 could have used an adapter 2.5mm taller, but the 17.3 and 14mm Delos could not. Hence, 10.5mm and it works with all TeleVue 1.25" eyepieces, even the 40mm Plössl, at the other extreme setting of the Paracorr. Virtually all the rest of the 1.25" TeleVue eyepieces use setting D with the 10.5mm tall adapter. They would all focus closer to the 2" eyepieces with the 16.5mm tall High-hat adapter, but then the 17.3mm and 14mm Delos would not have been able to come to focus, nor the 6mm and 8mm Ethos. The In Travel adapter allows the 17.3mm and 14mm Delos to be parfocal with all the other 1.25" eyepieces. It isn't necessary if you don't care about parfocality. But, a 10.5mm tall adapter allowed all the TeleVue 1.25" eyepieces to focus in the range of the Paracorr's travel, and no other height would have.

No, the Astrosystems ultra-low adapter is not an option. Here is why: The eyepieces in question are not small enough to insert into the recessed section of the Ultra-Low adapter. They will rest on the top of the adapter, just like they would in the TeleVue in-Travel adapter. However, the opening of the 1.25" bore in the TeleVue adapter sits only 5.5mm below the surface the eyepiece rests on, which is no problem--the setscrew will grab. In the Astrosystems Ultra-low adapter, on the other hand, the 1.25" bore starts 14.7mm below the surface the eyepiece rests on and the setscrew is many mm below that. The setscrew will likely miss the eyepiece entirely, or, at best, grab only the bottom couple mm of the barrel. It might work, but I could not guarantee it. That Ultra Low adapter works great with eyepieces small enough to fit into the recess, but not with eyepieces with shoulders too wide to fit into the recess. The TeleVue In-Travel adapter, on the other hand, has a shorter recess, so a wider eyepiece can rest on its top and still have enough barrel inserted to have it grab the eyepiece's barrel. I use the In-Travel adapter in the Paracorr with a 17.5mm Morpheus in my 12.5" because otherwise it cannot come to focus in the Paracorr, and the 17.5mm also rests on the top of the adapter, yet the 1.25" barrel inserts almost to the bottom of the adapter. I use all the Morpheus in the In-travel adapter in my refractor to make them closer to parfocal with other 2" eyepieces that require more out travel.

You should know the factory field stop dimensions on the Ultra Flat Field eyepieces are the actual physical field stops, not the virtual field stops that you see in the eyepiece. Without another repeat of a long-winded explanation, these are the actual field stops you see in the Ultra Flat Field eyepieces: 30mm --36.3 That is 33.5% wider than the 24mm ES 24x68 (2.1° becomes 2.8°) 24mm --27.5 18mm --21.7 15mm --18.2 10mm --11.2 The 30mm is narrower than the Aero ED, but not that narrow. It's a real 70°. By the way, there is a way to tell whether an eyepiece has pincushion distortion or barrel distortion at the edge. If you calculate a field stop assuming 0% distortion, it is = (apparent field ÷ 57.2958) x FL. 1) Example: the 24mm TeleVue Panoptic. A calculated field stop based on 68° is 28.5mm. Its actual field stop is 27.0mm. That means the 68° apparent field is created by stretching the field stop radially by 5.6% to yield a larger apparent field, so the eyepiece has pincushion distortion. If the calculated field stop had been smaller than the actual field stop, it would mean the edge of the field was compressed to yield a smaller apparent field than the field stop implied. 2) Example: 12.5mm Docter/Noblex 84° eyepiece with a calculated field stop of 18.3mm and an actual field stop of 19.2mm. That means the edge is compressed by 4.7% to yield only an 84° field, so the eyepiece has barrel distortion. The 30mm UFF 70° eyepiece has a calculated field stop of 36.65mm and an actual field stop of 36.3mm. That's pincushion distortion. The field stop is stretched by ~1% to yield the apparent field measured. That is very low distortion.

The small setscrew can be lightly tightened so you can simply rotate the eyepiece slightly to insert it. Not loose, but not tight. Then, eyepieces can be inserted and removed by slightly rotating them in and out. It sounds harder than it is. I've been doing it for years. It helps the setscrew has a nylon tip, so low friction. Now, if it turns out that your eyepiece barrels vary enough in size that some are loose and some are tight, then you may have to come up with another option. And if the eyepiece gets too loose when the setscrew hits the undercut on the barrel it could be a problem (all my 1.25" have smooth barrels). In that case, you may have to fill the undercuts on the barrels with metal tape to have them slide in and out easily. Or use the 2" Pentaxes in setting 3 and use the 1.25s in setting 5 and just refocus the scope, knowing the coma correction won't be ideal, but still a lot better than no correction.

Not all. Here are specs from Vixen Japan:

Yes.

If you can afford it, the 30mmUFF is a far better eyepiece.

Setting E on Paracorr II, and the middle setting (3) on a Paracorr I. The 30mm XW should use the same setting. Its focal plane is at the shoulder, just like the XW85°. The 3.5-20mm 1.25" XWs should use setting 5 (the lowest setting--1 is the highest setting) if used with the 1.25" Paracorr adapter, but that is still not optimum. Here is why: the Paracorr I has its focal plane at setting 3, the middle, when used as a 2" device. The focal plane is coincident with the 2" opening. That is why the 2" Pentax eyepieces will all use that setting--their focal planes are at the shoulder. the 1.25" Pentax all have their focal planes at the shoulder as well. But, the TeleVue adapter raises the eyepiece 10mm above the focal plane of the Paracorr I at setting 3. To get the XWs to the correct place means you need to drop the Paracorr top from setting 3 by 10mm, the height of the adapter. Settings on the Paracorr I are 1/8" apart, so lowering the top to setting 5, all the way down, only gets you 6.35mm of in-travel, which does not optimize the Pentax XW 1.25" eyepieces. You need to lower the top by another 3.65mm, but that is not possible. For the Pentax XW 1.25" eyepieces, you need the TeleVue In-Travel adapter, which gets you another 6mm of in-travel with those eyepieces (it gets another11.5mm of in travel with some 1.25" eyepieces). With that adapter, they can be used slightly above the lowest setting. You need that adapter for all 2" eyepieces that have their focal planes at the shoulder (e.g. Morpheus 4.5-14mm, Pentax XW 70, etc.). TeleVue 1.25" eyepieces have their focal planes 6.35mm below the shoulder, so can use the 10mm tall adapter. The Paracorr II's minimum setting is 10.2mm below the focal plane, so avoids this problem.

I'd like to clarify a few terms after reading your review: Ghosting is when internal reflections in the eyepiece for a bright object (like a planet) being viewed result in a slightly fainter image of the same object entering the opposite side of the field, and drifting across the field in the opposite direction the object is drifting, crossing in the center, and exiting the side opposite the side the bright object is exiting. Reflection is when a bright object reflects from the cornea back into the eyepiece and is, in turn, re-reflected back at the eye. Moving the head or eye causes the reflection to move all over the place. Glare is when a bright object immediately outside the field causes bright spikes, loops or flares inside the field of the eyepiece. Light scatter is when the field around the object is awash with light from the bright object, but internally scattered in the eyepiece due to poor coatings or rough lens surfaces. Your pictorial example is that of light scatter, not ghosting, unless the out of focus bright image drifts in the opposite direction as the planet as it drifts across the field, but with the head held steady.

That's exactly what I said. I was pointing out that the flat field doesn't cause any issue with the 30mm ES. Its problems are there in a flat field. A scope with a curved field would make its edge of field aberrations worse by defocusing them. Your Genesis is a fast f/ratio, which the ES doesn't deal with well. So, naturally, you see better images in the 31mm Nagler. It's not because the Nagler is better with a flat field, it's just better overall--less SAEP, same CAEP, and virtually zero edge of field astigmatism in fast f/ratios.

The 30mm ES 82° works fine in a flat field scope. It's main issue, other than SAEP and CAEP, is its outer field is not well corrected for astigmatism in a fast (<f/6) scope.

Astigmatism in eyepieces: https://www.handprint.com/ASTRO/ae4.html#astigmatism What other aberrations look like: https://www.handprint.com/ASTRO/ae4.html#

That depends. If the body of the prism diagonal is plastic (it looks like it is), al all-aluminum body would be an upgrade. You could use larger and/or heavier eyepieces more safely. If your scope is shorter than f/8, a mirror diagonal would result in less chromatic aberration on the Moon and planets than a prism. If either of those two circumstances is true, then a change might be an upgrade. Optically, though, in terms of brightness of image or image accuracy, it might be a wash. A dielectric-coated diagonal would also be equally durable in the long run. That assumes you have 3 or 4 eyepieces to cover a decent magnification range with the scope. That would come first, before a new diagonal.