Don Pensack
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Posts posted by Don Pensack
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I found reviews of them going all the way back to 2013:
Note that there are reviews on Cloudynights.com and StarGazersLounge.com
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electronic eyepieces that capture the image for download to a viewing device have been around for decades.
They did not incorporate the viewing screen into the eyepiece, and I recall them being wired, not wireless.
This might be the first example of an eyepiece that has an internal screen and can project the image wirelessly to a tablet, phone, or computer.
I saw a MallinCam on a big dob with a small tablet view screen hung on the scope in maybe the '90s?
This is only a very small step from that.
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The 24mm Hyperion has a true field 33% wider than the 17.5mm Morpheus.
If you have a 2" focuser, though, a 30mm UltraFlatField makes a better jump from the 17.5mm Morpheus and yields a true field 68% wider than the 17.5mm Morpheus.
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It was speculated the EOFB was due to its angular magnification distortion, except the Docter/Noblex 12.5mm has no EOFB and has strong AMD as well.
Baffles? Lens polish at the edges of the lens? Field stop too large? Unknown cause.
But I lent the eyepiece to five other observers, and they all saw the same thing.
If your circumstances don't allow it to be seen, keep it, because though tests show it's edge is only average at f/4, its other problem, FC, is very minor, and it was quite sharp at f/5.75.
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I find the APM 12.5 to have noticeable and objectionable edge of field brightening.
That's too bad, since otherwise it's fine.
The 12.5mm Morpheus is a great eyepiece--sharp, great contrast, easy to use. It's also lighter than the APM.
It's an easy choice, IMO.
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5 hours ago, Mr Spock said:
That isn't the finding of people who are using it. I find it just a little behind the 3.3mm TOE at the 3mm (3.5mm) setting.
The center and 50% points are very good. It's only at the edge the eyepiece image quality suffers.
As exemplified by the Moon photos and Ernest's measurements.
However, the figures at f/10 are very reminiscent of many inexpensive eyepieces.
It's only by f/4 (and likely f/5) that the eyepiece really falls down in edge quality, and then, likely outside the center 50% of the field.
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1 hour ago, Louis D said:
Has anyone discussed theories on the optical and mechanical organization of the Televue Nagler Zooms and the Svbony 3-8mm zoom? My theory, they have a 4 element image forming positive group up top and a 2 element negative, Smyth, group down in the insertion tube. To increase magnification, they simply move the two groups apart like a varifocal eyepiece such as my Speers-Waler 5-8mm "zoom". This also maintains the size of the AFOV as in the S-W. The mechanical trick to maintain near parfocality is to move the negative lens group downward during zooming in (higher power). I have to do this with the focuser knob to maintain focus while zooming in with the S-W.
In order to maintain parfocality, the upper and lower sections must move apart but one moves up while the other moves down.
That's why they look like mushrooms at the shortest focal lengths.
The Nagler Zoom has 5 elements in a 3 segment upper and 2 segment lower.
Al Nagler told me once that he could make a 15-30 zoom with an 82° field in the same manner, but it would be too expensive to sell, too heavy to use, and very fragile.
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From Ernest Maratovich's test of this zoom:
SVBony Zoom 3-8 8(8.1) 8.1 58(57,3) 56.9 2 6 15 diffr. 5 13 Ast. +6% zoom.. 7 7 57.3 56.5 3.3 5 20 FC,Ast. zoom.. 6 6 57.3 58.4 4 6 15 diffr. 5 11 FC,Ast. +14% zoom.. 5(5.2) 5.2 59.6(57.3) 57.3 4.5 7 20 FC,Ast. +14% zoom.. 4(4.4) 4.6 65.9(59.9) 59.6 6 7 25 diffr. 6 14 Ast. +15% zoom.. 3(3.5) 3.6 68.8(58.9) 59.8 8 8 45 diffr. 8 18 Ast. +15 The first column shows the focal lengths at the click stops (actual measured focal lengths in parentheses).
The next column is the field stop at each click stop. No mystery here, because focal length = field stop at 57.3° apparent field, and this is very close.
The next column is calculated field stops based on stated (and actual) focal lengths with no distortion. You can use these figures in Astronomy tools to get an accurate answer, or in TF = AF/M.
The next column is the measured apparent field (what we actually see). Roughly 57-60°.
Then 3 columns of spot size at f/4 (center/mid/edge) and 3 columns of spot size at f/10 (center/mid/edge). 5 is considered by most books to be perfect. 10 is fine as long as the spot stays round. 15 is OK and like many eyepieces at the edge. >20 is so-so.
The last column is the nature of the aberrations at that focal length, listed in importance from most to least, followed by a distortion %, if measured.
Conclusions: FC dominates from 5-7mm settings. Astigmatism is present from one end to the other. Distortion is fairly high for the narrow fields.
f/10 performance is better than f/4, but not remarkably so except from the 3mm to 4mm settings.
It has much better performance than most inexpensive eyepieces except at the 3mm setting.
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4 hours ago, Highburymark said:
Yes indeed Don - but this has always made me wonder why we don’t see more people having field curvature issues with the many brands of flat field eyepieces (APM, Altair, Lunt, SVBony etc)? As there’s field curvature inherent in many telescopes. I haven’t used any of that range myself, and I don’t doubt they are excellent, but why buy flat field eyepieces unless your scope has a perfectly flat field?
One reason I can think of is to reduce the amount of visible field curvature.
| + ) = ) You might be able to focus half way to the edge and accommodate the entire field.
| + | = | This is ideal, and reflectors of 1200+mm focal length are pretty flat, so this will work.
) + ) = | And this works if the eyepiece and scope have nearly identical curvatures,
) + ( = bad field curvature, and this can happen with a mismatch of eyepiece FC and scope FC.
Since we don't know (the manufacturers don't tell us) whether the FC in an eyepiece is positive or negative, the lowest risk is a flat field eyepiece.
But, alas, to the owner of a flat field scope, it doesn't matter whether the FC in the eyepiece is positive or negative--it'll be curved.
But, like the person with a flat eyepiece and curved focal plane scope, it might be possible to accommodate the curve, so the degree of FC is important as well.
I don't really under stand how short f/ratio refractors of 50-80mm don't see serious FC with nearly all eyepieces, though.
My 12.5" has a radius of curvature of ~1600mm. An 80mm f/6 refractor has a ROC of 160mm!! How any eyepiece wider than an ortho functions in such a scope is a mystery.
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One note: please go down the page to the next time the Buyer's guide was posted, as it contains some new entries.
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These are not new in the world.
Most resellers sell them as "Premium Flat Field" eyepieces.
Look up reviews on the Astrotech PF eyepieces to see some comments about them.
They are also sold by Artesky, Astromania, Astrotech, Auriga, Lacerta, Omegon, Sky Rover, Tecnosky, and Telescope Service.
FLO has a good price.
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5 hours ago, stormioV said:
I have just noticed these
https://www.firstlightoptics.com/ursa-major-eyepieces/ursa-major-fmc-flatfield-eyepiece-25mm.html
Would this be to similar to what I already have?
I'm still thinking uff 24mm or es68 24mm would be better option.
Argh! Another new eyepiece!
These are the same eyepieces sold by many companies as "Premium Flat Field" eyepieces. FLO is selling them at a good price.
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20 hours ago, Highburymark said:
I’m not picking up much field curvature at all - maybe it complements the opposite field curvature in my scopes? The 3-8 works well in all three of my refractors in this respect. In the F/6 60ED for example, just a tiny shift of the focus is needed at 3.5mm to make edge stars sharp.
On the issue of parfocality, it’s very close to parfocal through the range. I don’t need to refocus between 8mm and 5mm, but below that, a small tweak required.It is when curvatures match that you see a flat field. When curvatures are opposite, the edge is far out of focus when the center is focused.
FC is always more of a problem with larger field stops, too, so FC will be less visible at the 3.5mm end than at the 8.1mm end.
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And yet, people heat their secondary mirror or corrector plates or eyepieces to prevent dewing.
A very slight change in the optical image is preferable to the problem of opaque optics.
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On 16/04/2024 at 10:01, Zermelo said:
It may or may not be relevant to the decision that the Altair version (I have this one) has a steel body, and is heavier than some of the others.
[EDIT] I just looked it up, 331g
The Altair Astro version is heavier than 331g. In an early thread about the green eyepieces, someone quoted the actual weight, but, alas, I can't remember what it was.
The APM, with aluminum lower barrel, is 331g.
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I sold APM eyepieces for years.
On my gram scale the 24mm UFF was 331g without eyepiece caps.
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I have just posted the new 2024 Eyepieces Buyer's Guide here:
https://www.cloudynights.com/topic/919099-2024-eyepiece-buyers-guide/?p=13395818
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Place a bright star at the edge of the field, then look direct at the center of the field. If you can catch the bright star in your peripheral vision, you are seeing the whole field.
If you want to look at the edge of the field with direct vision, and you simply move your eye to do so, and the eyepiece is wider than about 70°, you will move your eye's pupil away from the eyepiece's exit pupil.
In order to look directly at the edge in an 82° eyepiece, you need to roll your head over and look through the eyepiece at an angle, whether using glasses or not.
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21 hours ago, stormioV said:
Thank you. 24mm uff looks great on the ruler matrix . My 25mm Starguider not so good.
If I struggle with long eye relief with my 32mm plossl, would that be similar case with 24 uff?
Possibly. Though that depends on how recessed the eye lens on your 32mm Plössl is.
I' have see 32mm Plössls with very deepset lenses which reduce the effective eye relief significantly and are not usable with glasses.
The 24mm UFF has a tall eyecup and a deeply recessed eye lens. Its 29mm of eye relief is reduced to about 7mm with the eyecup in the up position.
So it's likely you wouldn't have any issue with the large eye relief, especially with the eyecup flipped up.
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I sold a 21mmEthos and went to the 22mm Nagler due to needing glasses at the eyepiece.
I preferred the larger field, but glasses use dictated what happened.
FWIW, I don't feel deprived.
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2 hours ago, stormioV said:
Thank you for your help so far. It seems this version of uff is best priced in UK @£109
With field stop of uff being 27.66 mm compared to 27.2mm, of ES does this mean UFF will have a slightly larger /very similar fov? I thought UFF was 65 and ES68?
It means the Altair Astro 24 will have a larger True Field on the sky, but a slightly smaller apparent field. This is because distortion characteristics are different among the choices.
The difference in apparent field is small, and the extra true field is a nice bonus.
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4 hours ago, Second Time Around said:
I bought the 22mm/70 Deg Omegon Redline. Everyone's different but I preferred it to the much more expensive 22mm Nagler. It's supposed to be not quite as sharp as the Nagler at the extreme edge, but the shape of my eye sockets means that I can't see the very edge of many wide angle eyepieces anyway. I also found the Redline very comfortable as well. A further advantage is, as Louis kindly pointed out to me some years ago, it can take a Dioptrx astigmatism corrector that I prefer to wearing glasses.
It's currently £162 including VAT plus shipping from £6.90. Go to https://www.omegon.eu/eyepieces/omegon-redline-sw-22mm-eyepiece-2-/p,33239
It's the same eyepiece as the Astromania 22mm for $128.99 (£103.54). Even with VAT, it'll be cheaper than the Redline.
Also sold as Arcturus Ebony, and Omegon Redline. You might find a used one sold as an Astrotech AF70 or Olivon 70.
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3 hours ago, groberts said:
If I may, a couple of questions:
1. What's the eye relief of the APM?
2. Looking around, I see that using the APM as 1.25" can be a problem - any thoughts?
1. 18-20mm over the range.
2. Correct. It's focal plane is very high in the eyepiece. It will be easier to focus in most scopes if used as a 2" eyepiece.
It is usable as a 1.25" eyepiece if you have the large amount of in-travel required to get it to focus (it's over an inch).
The field stop in the eyepiece only requires a 1.25" barrel, so there is no difference in the image or apparent field if used as a 1.25".
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Short eye relief challenge
in Discussions - Eyepieces
Posted
They are used only for planets or close double stars, so the eye is held back far enough the field size is reduced.
Only recommended in scopes that track.