Don Pensack

Human vision has a sharp center of 2-5° wide. With an apparent field up to 68° or so, you can simply move the eye to look at the field, providing the image forms far enough away from the eye. With anything wider, moving the eye sufficiently to look at the edge will move the pupil of your eye off the exit pupil of the eyepiece. You have to roll your head over a bit to use direct vision to look at the edge. And, the wider the apparent field, the more you have to roll the head to look at the edge. If you stop to think of it, the edge of the field in a 100-120° eyepiece is closer to parallel to the scope than it is to perpendicular. Some people don't mind moving the head (I'm one), while others simply hate it (maybe they have arthritis in their necks?). Now, your peripheral vision extends to about 145° horizontal and 125° vertical, so seeing the edge of the field with peripheral vision when staring at the center of the field is easy. It's looking at the edge with direct vision where you have to roll your head.

3mm Delite. I had one, but floaters in my eye always interfered, even if the seeing was fantastic. It yielded a 0.43mm exit pupil in my 102mm f/7 apo. I now use a 3.7mm eyepiece as max power in that scope (0.53mm exit pupil), and it is marginal. You will have to have very clear eye, internally, to use the 3mm except on double stars. I also think the Delite's eye relief is more comfortable than the TOE's.

My experience with the UFFs is: --the 30mm is well corrected down to f/4.5 (maybe faster, but 30mm on faster scopes may not be advisable). "Best of Breed" in this series. Half the weight of other 30-31mm 2" eyepieces, and a lot better corrected than the 31mm Hyperion. --the 24mm is well corrected up to the edge but a little shy of the 30mm correction at the edge. Glasses compatible. More eye relief than any other maximum field 24mm (it has a 27.6mm field stop), with less rectilinear distortion than other 24mm max field eyepieces. --the 18mm is as well corrected as the 24mm and also glasses compatible. A small size for its field size. --the 15mm is a little less corrected at the edge and not glasses compatible. Nice in binoviewers. --the 10.5mm (it's not really 10mm) is fairly well corrected, but feels more like most inexpensive 60° eyepieces. Not glasses compatible. Very light and a small size.

Trying a bunch of "eyeglasses-friendly" eyepieces, I discovered that 14mm of effective eye relief (from the rubber up) is my comfort limit (actually, 14.3mm on the Apollo 11).. By pressing really hard and jamming my glasses into my eye socket, I can use as little as 12mm of effective eye relief, but it's not comfortable except as a test case to see if I can see the entire field. Pressing that hard is what I have to to with the new Pentax XW 85°. I'm on a search for a very low profile eyecup for those eyepieces, but haven't found one yet.

That 18mm UFF is only £109 from FLO. That is very inexpensive for such a well-corrected 65° eyepiece.

Yeah, by £50.

It is important to note that the field stops shown above for the UFF line are NOT the field stop figures we use for field of view determinations. It is confusing, but those are the mechanical stops that are modified by the lenses in the stack to yield different figures. The field stop figures of relevance to SGL viewers interested in calculating true field figures are: 10.5mm (actual focal length) --11.2mm field stop 15mm--18.2mm field stop 18mm--21.7mm field stop 24mm--27.6mm field stop 30mm--36.3mm field stop And yes, as noted, the Aero ED and the UFFs are two completely different eyepiece lines.

Well, technically, you'd adjust every eyepiece's focal plane to the working distance required. A few mm either way won't make a difference. That's why some people attach it to an extension tube and then simply use the extension tube as a "drop-in" accessory. If you want to be fussy about it, you could use it as a screw-on accessory and simply attach different spacers to each eyepiece to set the distance. I don't think most users would do that, though.

A number of people use the field flattener for visual. It works in scopes of f/4-f/9. You will need spacers to get to its working distance. Extension tubes will work if your scope has sufficient in travel left in the focuser. Otherwise, barrel extenders if attached directly to an eyepiece.

Last night the seeing was too poor to use high powers, so I went back and forth with a 30mm UFF, 22mm T4 Nagler, and 17.5mm and 14mm Morpheus. I have a 12.5" scope with Paracorr II, operating at f/5.75 with coma correction. I watched stars leave the field of view on all 3. In the 30UFF, the stars stayed tiny points right out of the field. The stars at the field stop were identical to the center. In the 22mm Nagler, some astigmatism became noticeable a few degrees in from the edge. The 17.5mm Morpheus was the weakest of the group, with very minor astigmatism in the star images from the 80% point to the edge. The 14mm Morpheus was seeing limited because of the magnification produced, but during some moments early in the evening I watched a star cluster leave the field still in tight focus with tiny pinpoint stars. But, I'll repeat what I've said before: the 14mm Morpheus in a Paracorr yields near-perfect stars across the entire field. I see no astigmatism or field curvature or chromatic aberration. I do in the 12.5mm, but not the 14mm. I trust that others do, but I just don't see it in the 14mm. Is it the Paracorr that corrects the eyepiece to that level? Or the f/ratio? I keep going back to this eyepiece because it is so sharp.

The issue isn't the eyecup, it's the cap. Change the cap to one that fits better and the problem goes away. Measure the diameter of the rubber eyecup when folded down and look for a cap with an I.D. 0.5-1.0mm smaller so that when it's pressed on it is tough to remove. And it will stay on. This is not a problem with just that eyepiece, many TeleVue eyepieces have caps that slowly inch their ways off the eyepieces just sitting there. The 24mm Panoptic is notorious for that.

Maximum possible eye relief with a 30mm lens at 82° = 17.26mm from a horizontal line across the eye lens. If the eye lens is concave, add the concavity to the 17.26mm figure to get the "from the glass" eye relief figure.

As long as your scope is longer than f/8, you'll like it. At f/5, I could see almost 50% of the field out of focus with astigmatism, so the Masuyama (which has excellent contrast, BTW) is not an eyepiece for the shorter f/ratios.

And, the zoom is the equivalent of 11 eyepieces spaced a half mm apart, or 21 eyepieces space 0.25mm apart, etc. Can't beat the price. It has some issues (eye relief at the short end), a longer-than-average 1.25" barrel, etc., but so do other inexpensive eyepieces.

Meade is owned by Optronic Technologies, Inc, a US company, owner of Orion in the US. The scopes are imported, and 99.9% likely to have metric threads.

Look up a Baader Contrast Booster filter to see more details on Mars. "Fireflies dancing about" is an apt description for reflections from the cornea to the eyepiece and back again. Not all short focal length eyepieces are prone to this, but stay away from Kellners and Erfles as these are notorious for that. Fully multi-coated Plössls are often good, but eye relief gets really tight about the 8mm range. A suggestion I could make is to Barlow a longer focal length eyepiece you know doesn't have the problem. It often is sharper across more of the field, too, because the Barlow doubles or triples the f/ratio of the scope before the light enters the eyepiece, making the incoming rays more parallel, which reduces induced astigmatism in the eyepiece. That really cleans up inexpensive designs like Plössls, Königs, and inexpensive widefields.

Mars is still a decent size till about the end of the month.

The 30mm is in a different league. It's truly a high-end eyepiece. You won't be disappointed. It's a real 70°. And sharp down to f/4. KUO really has a superb eyepiece here, with the 30mm--contrast and sharpness are excellent.

Its presence is less noted the shorter the focal length. It was present in all of them, but the 14mm was the worst, the 10mm a bit better and the 7mm and shorter weren't bad enough to have much impact. But then, I didn't use them on the moon, and a smaller pupil diameter would have made them harder to use.

As counterpoint to the zoom argument: --zooms have narrow fields of view compared to fixed focal length eyepieces. Generally, wider is better--more engaging. --zooms provide too many in-between powers. If your scope yields 50x, you really don't need a 60x or 70x eyepiece. When you change the magnification, you want there to be a visible difference. With the zooms I've used, I pretty much always used them at 4-5 settings and skipped the in between settings. --no zoom I've tried, and that includes the Leica Aspheric, was the equal of separate eyepieces in edge of field correction, lack of spherical aberration, sharpness of star images, lack of edge of field brightening, or contrast. (well, the Nagler Zoom was, but I wanted more than a 50° field). Fixed focal length eyepieces can be better (though not all are, of course, which is why to read reviews) that zooms, and if you have those better fixed focal length eyepieces, returning to zooms is not a viable option. Which is why I have advocated for a starter set of 3 eyepieces to get your feet wet in astronomy: https://theskysearchers.com/viewtopic.php?t=18374

The StellaLyra makes the 9th label of the 30mm available. But it is quite cost-effective. Kudos to FLO.

Cameras can capture things invisible to the eye, but the view through the eyepiece can encompass a greater dynamic range. You can see the Trapezium in M42 at the same time you can see wisps of nebulosity in the Fish Mouth. You can see details in the Regio Centralis at the same time you can see the very faint nebulosity almost a degree away that closes the oval. Here is a sketch that captures what can be seen visually, which would be an impossible image: https://www.cloudynights.com/topic/399146-sketch-of-m42-m43-dobsonian-22/?p=5112451

If you were a visual observer, you'd appreciate that: There is a lowest power that works in the scope. There is a highest power that works in the scope. The range of usable magnifications is likely a 15:1 range or larger. Seeing conditions often limit the maximum to a lower power than the highest. You want the magnification changes to represent a noticeable difference when you move up in power. Objects in the night sky come in a huge variety of sizes, from, perhaps, an arc second up to over 14,000 seconds. needless to say, the magnification for one is not the right magnification for the other. So, to yield a reasonable range of magnifications, you will need around 6-8 eyepieces. And if planetary observing is a featured use, due to the seeing conditions, many like to have several high power eyepieces close together to accommodate the fact each night may have a different highest power usable. I think people build up much larger collections of eyepieces because they have multiple telescopes, or because they simply don't get rid of older, unused ones.

It looks like there is evidence the lower retaining ring was loosened and retightened with a tool that had blades wider than the slots in the retaining ring. And that caused the scuffing on the paint. However, I'm a bit concerned about the stuff on the lens right inside the retaining ring. Either the lens is filthy or, maybe, the same tool that chipped the paint scratched the lens as the ring was tightened. I hope not, and that it cleans right off with a cotton swab and some alcohol.

This process, called "blinking", doesn't work well in light polluted environments because the ambient light reflecting off the nebula filter is brighter than what can be seen through it. It works OK in really dark skies, but, as a technique, its true value is in planetary use, where you can quickly see what filter you want to use to yield the detail you want to concentrate on.