Louis D

No one really knows for sure if these are or are not blems that didn't pass the ES/Bresser quality control check. I've read of people being satisfied with these rebrands, and of others having issues with theirs.

No, I wouldn't either. But someone in China paid an optical designer somewhere to interpolate/extrapolate Thomas M. Back's 30mm and 40mm Paragon designs to add a 35mm design. It would not be absurd to think they'd do it again with the 30mm UFF design to adapt/scale it up or down.

I often refer back to my copy of Telescope Optics: Evaluation and Design by Harrie G. J. Rutten and Martin A. M. van Venrooij. Sky & Telescope took over Wilmann-Bell's catalog, so it might show up again in a new printing. It mostly covers telescope optics and spends only a single chapter on eyepiece optics. Still, it's an educational read that is less dense than telescope-optics.net. It's still dense, but not overwhelmingly so.

I do have to wonder what makes refractors so much heavier than their Newtonian size equivalents. Are two or three hunks of 5" or 6" diameter refractor glass that much heavier than one hunk of 5" or 6" mirror glass? Is it that the refractor lens cell is much heavier than a Newtonian mirror cell?

Don't drive much in Canada, do you? It always freaked me out driving from Michigan to New York by way of Ontario to see all road signage in km instead of miles. Now, you need a passport to drive through Canada, so I just take the slightly longer way through Ohio (your stomping grounds) and Pennsylvania. That, and the border security lines became unbearable over the last 40 years.

Warning! Esoteric computer hardware discussion ahead: The problem with octal versus hexadecimal is that you need only 3 bits to represent octal digits versus 4 bits for hexadecimal digits (hexits). This leads to a problem when storing values in memory locations that tend to be in multiples of 8 bits (1 byte) in modern machines (they were multiples of 6 bits in older machines, so octal worked). Hexadecimal packs nicely with 2 hexits per byte and no waste. Octal packs as 2 octal digits per byte with 2 bits wasted. Thus, the shift about 40 or 50 years ago from octal to hexadecimal digits along with the shift from memory words in multiples of 6 bit to multiples of 8 bits. If the octal digits are allowed to spill across bytes for packing efficiency, it becomes difficult to read memory dumps aligned on byte boundaries.

Are all the tripod fittings 100% metal with no plastic parts?

I'm sure it would have been overkill and expensive as you say to go with 9 elements and an exotic telecompressor design when a more traditional Smyth group negative/positive design would suffice. I'm sure it would have created a niche following, though. I would like to see the 30mm design pushed until the telecompressor field lens fills the 2" barrel. It's only a bit over 40mm wide in the 30mm UFF. I looks like it could be pushed to having a 46mm clear aperture. The upper barrel elements might have to grow wider as well if the design is simply scaled. The internal field stop would grow to 35mm from 30.4mm. If all remains linear, the effective field stop would grow from 36.4mm to 41.9mm, or roughly the same as the 31mm NT5. The focal length would probably grow from 30.3mm to 34.8mm, or roughly the same as the 35mm Panoptic. It would have a 3mm larger field stop diameter than the Pan and probably be somewhat lighter and slimmer. Is KUO listening?

I'll have to look for EOFB sometime in it. I once noticed my 12mm NT4 had brightening all the way to the center. Only a small point appeared to be relatively dark in the center. I swapped it with my 12mm ES-92, and the brightening went away. Swapped them again, and the brightening was back. I'm not sure what was going on that night, but it was highly disappointing to see in a TV product. I even checked for fogging, but there was none. I'll have to do a test sometime with those two plus the 13mm Redline, 12.5mm APM Hi-FW, and 14mm Morpheus. It might even be scope specific. I can't remember which scope I saw the EOFB in the NT4, but it was probably my Dob.

Having grown up in the 70s/80s in the US, we were constantly told to be ready for the inevitable switch to the metric (SI more properly?) system. It never happened. The US kind of stalled out part way there. Engineering uses SI units for the most part. Day to day living uses customary units. I've got to admit, talking about how tall someone is in feet and inches seems much more intuitive than in meters, decimeters, and/or centimeters. Pounds/kilograms, inches/centimeters, miles/kilometers are each close enough by themselves that I could make the switch eventually. The mix of units for everyday nuts and bolts is a bit of a pain. Of course, wire and nails have their own systems of units that are neither customary nor SI. I'm still waiting for the SI version of time keeping with 10 hours per day, 10 decihours per hour, 100 centihours per hour, etc. I'd love to see how they shoehorn 100 or 1000 days per year against the solar calendar. Why was 10 chosen as the base? Base 12 makes a lot more sense. It's divisible by 1,2,3,4,6, and 12. 10 is only divisible by 1, 2, 5, and 10. Being a computer engineer, I've grown quite adept at base 16 or hexadecimal arithmetic, so it should be doable to work in base 12. I do often prefer the use of customary units' fractions to decimals for day to day functions as opposed to engineering usage for taking a swag at a measurement.

As you can tell from my eyepiece AFOV image above, the APM UFF 24mm performs quite well at f/12, has a 63° measured AFOV, a 65° effective AFOV, a 27.5mm measured field stop (as big as you can go, with a bit of field stop fuzziness), and 17mm of measured, usable eye relief. It is quite usable with eyeglasses and sharp to the edge at f/12 (and probably f/10 as well). I already had 2" diagonals and eyepieces, so I just needed to get the MCT to SCT thread adapter and an SCT 2" visual back for my 127 Mak. I think those two together were under $50 pre-inflation. The loss of illumination is surprisingly hard to notice visually with 2" eyepieces. The astonishingly wider true field of view is not. The only annoying artifact is when a bright star or planet passes the edge of the 27mm rear port. It starts reflecting off the rear baffle and creates an oval artifact in the field of view. I keep meaning to flock that baffle tube to see if I can minimize or eliminate this. You could try to hunt down an 80s or 90s vintage 30mm/32mm Plossl with the eye lens mounted nearly flush to the top of the eyepiece. Apparently, enough non-eyeglass wearing folks complained about it being hard to hold the exit pupil in them, so practically the entire marketplace recessed the eye lenses of their longer focal length Plossls. I can just use my 32mm GSO Plossl with glasses, but not my 26mm Sirius Plossl. There are a bunch of 80s/90s/early 2000s vintage, Japanese made 1.25" Konigs in the 24mm to 32mm range that come up occasionally in the classifieds, at least here in the US. They also had their eye lenses mounted almost flush to the top of the housing, and so should be usable with eyeglasses. They typically had a 60° to 65° AFOV. They perform fine at f/10. You could also keep an eye out for the discontinued Meade 5000 Plossl line. They had a 60° AFOV and are basically the same as the overpriced ES-62 line. All had their eye lenses mounted flush to the top, have a removable twist-up eye cup (with a bit of work), and should have enough eye relief in the 26mm version for eyeglass wearers. I have the 40mm 2" version, and it is a really nice eyepiece at f/12. The outer 50% of the field is fuzzy at f/6, so not recommended in faster scopes. Not widest field, but still a nice, cheap eyepiece at f/12 (probably f/10 as well) is the SVBONY 68° Ultra Wide Angle 20mm. It has enough eye relief to be usable with eyeglasses and is basically sharp to the edge at f/12. It has a 23.7mm measured field stop. It does better than the Orion SWA as can be seen below. I use a pair in my Arcturus binoviewer for widest field viewing.

Are you saying that even at f/10 those two Hyperions are not sharp to the edge? If so, are they pretty close to that goal? By way of comparison, my 13mm and 17mm Redlines (Astro Tech AF70 version) massively improve going from f/6 to f/12, but not quite perfect. They are very similar to the Hyperions in design parameters, so I would expect similar improvement.

Literally every one of my eyepieces but those two I mentioned above make extended objects appear larger and larger as they approach the edge; thus higher magnification at the edge than in the center. It's pretty obvious in my ruler images. Put another way, the moon gets stretched into an egg shape with the large end toward the edge in practically all eyepieces to some extent. By way of comparison, those two eyepieces I mentioned compress the moon's side facing the edge. Perhaps we're describing edge magnification in different terms. I'm describing in terms of area of the AFOV covered which is a rectilinear description, I believe.

The Hyperions are basically a Chinese made knock off of the Japanese made Vixen LVW line. They are not as well corrected as the LVWs (or XWs, Delos, Morpheus, etc.), but might suffice at f/10. The exception might be the 24mm which is basically an improved Erfle design and is considered to be the worst of the line. I'd really like to know what it is about the 25mm Plossl and 8-24mm Celestron zoom that rub you the wrong way to be able to judge if you would like the Hyperion line. I have no doubt you'd love the Morpheus line, and they're on sale both in the US and the UK right now. You might be able to squeeze in 3 Morpheus on your budget if you order from FLO (this site's sponsor) because you'd save on a cheaper sale price and on lack of sales tax. It would be $600 shipped for 3 at today's exchange rate versus $747+shipping+tax from a US retailer. There's no import duty into the US as long as your order is below $800 dollars. I have the 9mm Morpheus (bought from a UK store during a sale), and it is nearly as aberration free as my 10mm Delos at f/6.

Missed that in the OP's sig. So, short of going the 2" route I suggested, the real question is, what does the OP hope to improve upon versus the NPL 30mm? Wider apparent field of view at slightly wider true field of view with the 24mm APM UFF, but with a smaller exit pupil; or narrower apparent field of view at slightly wider true field of view, but with a larger exit pupil? Only the OP can answer that.

I've only got two eyepieces in my collection that have this property, at least in terms of radial magnification. One is the APM Hi-FW 12.5mm and the other is a vintage Bausch & Lomb 15x WF (16.7mm) microscope eyepiece. You can see this manifested as the millimeter tick marks growing closer together nearing the edge in my ruler images. Below are the two group shots showing this. APM Hi-FW 12.5mm which is 12.6mm on axis and 13.4mm at the edge: Note that the APM squeezes in more true field in a narrower apparent field than does the 12mm ES-92 at just 0.6mm longer focal length on axis. It's a pretty neat trick. Bausch & Lomb 15x WF which is 17.1mm on axis and 17.5mm at the edge: It makes sense that a microscope eyepiece would try to minimize magnification distortion across the field for research purposes. There is some tangential magnification growth in both going from center to edge as can be seen in the bowing edges of the rulers. It's just that it's a lot less in these two than in the other eyepieces. I'm sure there's a way to work out angular versus rectangular distortion from these two types of magnification changes, but I haven't studied optical theory enough to know what it is.

Not in my experience. Only a very few eyepieces yield less magnification at the edge than at the center, at least in a linear manner rather than an angular manner. I'll have to work out how to measure angular magnification someday.

Just about anything look good at f/12. I would just get a 32mm Plossl for now. If you want to go truly wide on that Mak, and you don't mind a bit of vignetting, you can fit a 2" visual back and use a 2" diagonal and 2" eyepieces with one. That's how the US versions are sold. Here's a through the eyepiece comparison of the true field of view when bumping up from a widest field 1.25" eyepiece to a widest field 2" eyepiece using this strategy: Notice how much more true field is visible. Yes, the edges are 65% as bright as the center, but it's a trade off I'm willing to live with.

Well, you'd have to refocus for the edge of field to see if the edge sharpness returns to be able to definitely assign the blurriness to field curvature. My Pentax XL 14mm has near perfect edge correction, but it also has significant field curvature. When I bought it in my early 30s, it looked sharp edge to edge. Now in my late 50s, I have to refocus it to see that sharp edge again. If when refocused for the edge it is still unsharp out there, you're probably dealing with astigmatism issues. This assumes you've got a coma corrector in your 130PDS. Without one, you'd be seeing quite a bit of coma as well. Setup a pinhole light with some foil and a flashlight (torch) in a darkened room for more advanced testing. Getting the pinhole small and round enough is the problem in my experience with this approach. Alternatively at night, put a fairly bright star in the center and slew it to the edge. See if it goes blurry. Refocus it to see if gets sharp. Look at the shape of the star on either side of best focus. If it alternates between radial and tangential lines on either side of best focus, that's classic astigmatism. If it simply looks comet like, pointing to the center, that's classic coma. It can look like a combination of those two. Commonly, chromatic aberration is also thrown in for good measure making pretty rainbows out of the star.

With FLO's sale on these, that works out to £152.50 or $191.50. Add in shipping, and the total comes to $216.78. Not quite as cheap as from continental Europe, but close; and I'm pretty sure FLO will ship them to the US. It's certainly cheaper than from US retailers, especially when you factor in they have to charge US sales tax and international sellers don't. Being under $800, import duties are not an issue, either. I'll have to think about picking up another Morpheus now. 🤔

They're $185 Euros in Germany (no VAT to US). This equates to $203. Factor in no sales tax or import duties and $30 shipping, and you're slightly ahead, especially if you can't get free shipping and a seller that doesn't charge your state's sales tax here in the US. I've bought all of my Morpheus eyepieces from the UK in the past for these reasons.

Same here in the US. They won't ship to any country with an official Baader distributor different from themselves.

No, it's a legitimate train of thought if correctors could be produced in the price range of line filters. Why filter if it costs about the same to correct? The problem is, back 15+ years ago when the Chromacors were new, they were a $1000+ corrector for $300 to $600 achromats. As lower cost ED and APO refractors started coming onto the market, the economics of it made no sense.

If they weren't so expensive for what they are, I would like to get a 1.25" version to compare to my 2" Yellow K2 filter that I bought for under $10: From the Baader spectrogram, it appears very similar in that it just barely let's through the H-β line: If you want to cut down on the yellow cast, just pair it with a Neodymium or Moon & Skyglow (Didymium) filter to cut out the pure yellow part of the spectrum. That's basically what Baader did with their Contrast Booster filter: You also lose a bit of the green portion of the spectrum as well, so I'm not particularly fond of this approach except when looking at certain planets like Jupiter that benefit from this.

My understanding from reading up on CN about the Chromacor is that Valery Deryuzhin at Aries Optical (in Ukraine) was utilizing some exotic surplussed Soviet glass of unusual dispersion properties that isn't normally produced and is very expensive to have a new melt poured. Thus, we're not likely to see them made again anytime soon unless a Chinese glass producer surpluses some after making a similar optical production run for their government. I'm not holding my breath waiting, though. There's a bunch of Chromacor reviews here for anyone wanting to read up on them.