79 replies to this topic

[Starman1]

I don’t get the joke?

If KUO stops shipping to the USA won’t that mean AstroTech telescopes and many eyepieces presently sold by Astronomics will be unavailable once existing stock runs out?

Astrotech has other sources.

[SeattleScott]

"30UFF... the exit pupil will be large, but probably not show secondary shadow?"

That would be important to know, where I sometimes see secondary shadows. Other than that, it sounds suitable for both telescopes, and a real value buy.

Do you have a 30-32 Plossl? Try it out and see if you see shadow.

[Joe Cepleur]

I have a 32mm Plossl and have seen the shadow of the secondary, but I need to better catalog when I see it. I'm not surprised or disturbed to see it during the day. I'll test it on a bright Moon as soon as the skies and clouds allow. 

 

Does this mean that the focal length of the eyepiece matters to seeing the shadow, but not the apparent field? Is that because when comparing two 32mm eyepieces, the apparent size of everything including the shadow remains the same, even as the wide field eyepiece somehow is able to display more of the available light from the edges of the image cast by the objective? 

[csrlice12]

The Chinese could just decide  to drastically cut back on production of eyepieces and other gear...we could be in for a dry spell.

[Starman1]

I have a 32mm Plossl and have seen the shadow of the secondary, but I need to better catalog when I see it. I'm not surprised or disturbed to see it during the day. I'll test it on a bright Moon as soon as the skies and clouds allow. 

 

Does this mean that the focal length of the eyepiece matters to seeing the shadow, but not the apparent field? Is that because when comparing two 32mm eyepieces, the apparent size of everything including the shadow remains the same, even as the wide field eyepiece somehow is able to display more of the available light from the edges of the image cast by the objective? 

Yes, what matters is exit pupil/magnification/focal length when it comes to having the secondary shadow be visible.

And the pupil diameter of the pupil in your own eye, of course.  Apparent field is irrelevant.

 

Don't see the shadow?  Look at something bright, like the Moon, and suddenly the shadow is there.

If your pupil shrinks, the shadow can be more visible.

 

But, I don't care what scope you have, a 32mm is too low a power for the Moon and planets.

If you avoid daylight use and avoid looking at the Moon or planets at low power, you'll never see the shadow of the secondary, even in an SCT.

[SeattleScott]

Yes, what matters is exit pupil/magnification/focal length when it comes to having the secondary shadow be visible.
And the pupil diameter of the pupil in your own eye, of course. Apparent field is irrelevant.

Don't see the shadow? Look at something bright, like the Moon, and suddenly the shadow is there.
If your pupil shrinks, the shadow can be more visible.

But, I don't care what scope you have, a 32mm is too low a power for the Moon and planets.
If you avoid daylight use and avoid looking at the Moon or planets at low power, you'll never see the shadow of the secondary, even in an SCT.

Well, I see secondary shadow using a 40mm eyepiece at F10, but admittedly that’s different than a 30mm eyepiece at F4.6. But I’m only 50.

[Starman1]

Well, I see secondary shadow using a 40mm eyepiece at F10, but admittedly that’s different than a 30mm eyepiece at F4.6. But I’m only 50.

Human pupil diameters vary all over the place, from 2mm to over 8mm Mine are only 4mm, dilated at night. Good for resolution, but not the best for low powers in a telescope.

[Jon Isaacs]

 

 

But, I don't care what scope you have, a 32mm is too low a power for the Moon and planets.

If you avoid daylight use and avoid looking at the Moon or planets at low power, you'll never see the shadow of the secondary, even in an SCT.

 

I agree with your prescription for avoiding seeing the shadow of the secondary... 

 

And for seeing the moon in detail, a 32 mm eyepiece is too long for just about any telescope.

 

But, my most glorious view of the moon, 118x, the 31 mm Nagler in my 25 inch operating at F/5.75.

 

It just appears like a giant rock suspended in space...

 

Jon

[Polyphemos]

Astrotech has other sources.

For other gear manufacture by companies other than KUO, but isn’t KUO the maker and primary source for AstroTech telescopes and many of the UFF, UWA, and XWA eyepieces?

[Joe Cepleur]

My only reason for looking at the Moon through a 32mm Plössl is as part of a methodical experiment, not as a target for observation per se. Today, I tested all of my most used eyepieces (all 1.25") in daylight in the 6" f/4 Doblet (a new word for "mini-Dob!"), knowing I would see shadow, but wondering how short an eyepiece had to be before the shadow disappeared. The answer is about 20mm.

Toning down the brightness from full daylight, I will repeat this with a bright Moon. Then, try with Jupiter, both in the partial darkness of early evening and at night. This is easy enough to do when I am observing anyway, and could yield a clear sense of under what circumstances the shadow becomes a problem. Might seem odd that I care, but I remember a problem with the 32mm Plössl unexpectedly showing the shadow at a star party where I had not expected to see it, so now I am curious just what kinds of objects and levels of illumination cause the problem.

(Whoa... Scratch that testing on Jupiter! Just looked outside, and saw it setting just as it was getting dark!)

Edited by Joe Cepleur, 10 May 2025 - 08:30 PM.

[Starman1]

For other gear manufacture by companies other than KUO, but isn’t KUO the maker and primary source for AstroTech telescopes and many of the UFF, UWA, and XWA eyepieces?

But not the maker of the Plossls and Paradigms or many other brands Astronomics sells.

[Polyphemos]

But not the maker of the Plossls and Paradigms or many other brands Astronomics sells.

Ok, well I guess it would be unfortunate for a Astronomics, and for the rest of us who purchase KUO gear through Astronomics, for them to lose a long-term and valuable business partner however temporarily, which is why I was confused by the emojis which seemed to me to convey a positive outlook to the prospect. I must have misunderstood.

[Starman1]

Ok, well I guess it would be unfortunate for a Astronomics, and for the rest of us who purchase KUO gear through Astronomics, for them to lose a long-term and valuable business partner however temporarily, which is why I was confused by the emojis which seemed to me to convey a positive outlook to the prospect. I must have misunderstood.

I meant to imply it would not be a disaster for the US.  Here, there are only a few dealers importing their eyepieces.

It's not a good thing, though.  KUO makes some of the best products from China out there.

Astronomics sells 7 brands of eyepieces, and some of the products from 3 of them are from KUO.

 

Re-reading the note, however, it seems KUO has merely stopped selling their house brand directly to American consumers.

It doesn't seem like they have stopped shipping private label products to retailers/distributors.

What remains to be seen is how much they will cost.  A $1000 product might not be viable at $2400.

 

The possible huge increase in prices from Barsta, KUO, iOptron, etc.etc.  Is bound to have an effect, if the product is even available to buy.

To get back to the thread's purpose, this will affect the prices of inexpensive eyepieces as well as the expensive stuff.

Low priced 2" eyepieces will suddenly not be low priced any more.

 

Note to all: don't put off the purchase of anything--shop while prices are still low.

[Joe Cepleur]

Amazingly, after a day of rain, the clouds cleared at nightfall, so I now have an answer about seeing the shadow of the secondary. I had thought that, since the shadow shows prominently in daylight, I might have seen it when observing the Moon, at least with longer focal length eyepieces. But, there was no shadow to be seen!

 

When I then turned to the stars, the result was unexpected. When my eye was not placed exactly where it needed to be — when it was somewhat off-center or too close — hints of the shadow appeared. They were not clear, but were oversized blurs that moved and changed size and faded in and out of visibility as my eye found center. They were distracting and annoying, but because there was no shadow when my eye settled where it belonged, I am comfortable adding a 30mm to 40mm 2-inch widefield in this range. 

 

Unexpectedly, the mild appearance of shadow was much more prominent with my 32mm Plossl than with my 40mm Plossl, but they are of different brands. Somehow, the 40mm's design results in less shadow, despite its longer focal length. 

 

My current 1.25-inch eyepieces are sharp enough right to the edge of the mini-Dob's field, so I have decided to stick with them for that scope, so that a gradually growing collection of 2-inch eyepieces could better enhance the much greater potential of the 6" f/10 refractor. 

[Starman1]

Amazingly, after a day of rain, the clouds cleared at nightfall, so I now have an answer about seeing the shadow of the secondary. I had thought that, since the shadow shows prominently in daylight, I might have seen it when observing the Moon, at least with longer focal length eyepieces. But, there was no shadow to be seen!

 

When I then turned to the stars, the result was unexpected. When my eye was not placed exactly where it needed to be — when it was somewhat off-center or too close — hints of the shadow appeared. They were not clear, but were oversized blurs that moved and changed size and faded in and out of visibility as my eye found center. They were distracting and annoying, but because there was no shadow when my eye settled where it belonged, I am comfortable adding a 30mm to 40mm 2-inch widefield in this range. 

 

Unexpectedly, the mild appearance of shadow was much more prominent with my 32mm Plossl than with my 40mm Plossl, but they are of different brands. Somehow, the 40mm's design results in less shadow, despite its longer focal length. 

 

My current 1.25-inch eyepieces are sharp enough right to the edge of the mini-Dob's field, so I have decided to stick with them for that scope, so that a gradually growing collection of 2-inch eyepieces could better enhance the much greater potential of the 6" f/10 refractor. 

What you describe is what happens when you get inside the exit pupil of the eyepiece.  It is not the shadow of the secondary, but the iris of your eye intercepting the light from the eyepiece, producing "oversized blurs that moved and changed size and faded in and out of visibility as my eye found center. They were distracting and annoying, but because there was no shadow when my eye settled where it belonged."

That description is a perfect description of being inside the exit pupil, too close to the eyepiece.

[Joe Cepleur]

The 32mm Plössl has a 54⁰ apparent field, whereas the 40mm has a 45⁰ apparent field because the light gets clipped by the 1.25" barrel. So, I'm seeing the inside of all of the exit pupil of the 32mm, but only a central portion of the inside of the 40mm's exit pupil. There is actually more light hitting my eye from the 32mm, which somehow increases the effect over the 40mm. Any 2-inch eyepiece I would get would be used in a telescope of much longer focal length and so would have a much smaller exit pupil, so I would never get inside it.

And, regarding my night vision: I still don't know whether my pupils open larger than is typical of my age. I was not seeing the shadow of the secondary, so this was not a test.

[Jon Isaacs]

The 32mm Plössl has a 54⁰ apparent field, whereas the 40mm has a 45⁰ apparent field because the light gets clipped by the 1.25" barrel. So, I'm seeing the inside of all of the exit pupil of the 32mm, but only a central portion of the inside of the 40mm's exit pupil. There is actually more light hitting my eye from the 32mm, which somehow increases the effect over the 40mm. Any 2-inch eyepiece I would get would be used in a telescope of much longer focal length and so would have a much smaller exit pupil, so I would never get inside it.

 

 

32mm Plossls generally have a 50 degree AFoV and the light is clipped by the 1.25 inch barrel in exactly the same way the light is clipped by the barrel of the 40mm Plossl.  Both have ~27 mm field stops in a barrel with a 28mm inner diameter.

 

The exit pupil depends on the focal ratio, not the focal length.. My largest scope is F/4.4 with a 2450mm focal length.. The exit pupil with a 32mm eyepiece is 7.3mm.

 

Jon

[Starman1]

The 32mm Plössl has a 54⁰ apparent field, whereas the 40mm has a 45⁰ apparent field because the light gets clipped by the 1.25" barrel. So, I'm seeing the inside of all of the exit pupil of the 32mm, but only a central portion of the inside of the 40mm's exit pupil. There is actually more light hitting my eye from the 32mm, which somehow increases the effect over the 40mm. Any 2-inch eyepiece I would get would be used in a telescope of much longer focal length and so would have a much smaller exit pupil, so I would never get inside it.

And, regarding my night vision: I still don't know whether my pupils open larger than is typical of my age. I was not seeing the shadow of the secondary, so this was not a test.

Actual measurements of 1.25" eyepieces:

32mm Plössls range from 43° to 49.5°

40mm Plössls range from 38° to 43°

Exit pupil depends on the scope's f/ratio and the eyepiece's focal length:   Exit pupil = eyepiece focal length / telescope f/ratio.

 

True field is the same on both 32mm and 40mm (they have field stops limited by the barrel), so the only reason for 40mm is in very long f/ratio scopes to get a larger exit pupil for a brighter image, say, f/8 and longer.

[Joe Cepleur]

True field is the same on both 32mm and 40mm (they have field stops limited by the barrel), so the only reason for 40mm is in very long f/ratio scopes to get a larger exit pupil for a brighter image, say, f/8 and longer.

Interesting. For years my longest eyepieces were a 40mm and a 25mm. After I got a 32mm, I found that I often preferred the 40mm. Now I know why. I was using it with an f/15 small refractor, which needed all the brightness I could get. 

[T1R2]

Interesting. For years my longest eyepieces were a 40mm and a 25mm. After I got a 32mm, I found that I often preferred the 40mm. Now I know why. I was using it with an f/15 small refractor, which needed all the brightness I could get. 

Even on my 60mm I still prefer the 32mm, for its better resolution.(slightly higher mag) 

[Joe Cepleur]

Today I purchased a "gently used" 2-inch, 30mm Ultima Edge Flat Field Eyepiece directly from Celestron's Website for a few pennies under U.S. $210 with free shipping. It is a customer return that is guaranteed to work as well as a new one and carries the same warranty and return privilege, although its "gentle use" may have brought it some minor cosmetic blemish. I would not be surprised if it proves to be identical to new. 

 

Thanks to all of you for your help, and special thanks to Don for steering me at the end over a few private messages. It is remarkable how much there is to know about eyepieces once one steps away from the simple eyepieces traditionally used with long-focus, classic telescopes, and even more remarkable that so many of you have detailed knowledge of the specific idiosyncrasies of seemingly every eyepiece on the market. 

 

This is not an eyepiece I would have thought to buy had it not been for this thread. I had originally intended something longer, but had not understood how special, wide-field optics could make a shorter eyepiece show as much sky as a longer one. Don said that, at this price point, good edge correction was rare, but that this eyepiece had it. So, Mr. Value Buyer here finally found an "inexpensive" eyepiece that begins to rival finer ones. 

 

This really cool simulator helped me to decide:

 

https://telescopius....scope-simulator

 

After loading the various eyepieces I was considering into it along with my telescopes, it showed me the resulting images. Much as my 12x50 binoculars show me more stars than my 8x40, the simulator shows this 30mm wide field revealing more stars than would be seen in other eyepieces of longer focal length, while only slightly reducing the true field. Neat trick! I'll have to hope that the simulator accurately models real telescopes! 

 

Thank you, everyone, for your help. I'll have to report back on how well the eyepiece works! 

[Joe Cepleur]

For what it's worth, while shopping for various eyepieces, I really did see a run on purchases, as presumably every other astronomer was also trying to beat the tariffs. Several times, I returned to reconsider an eyepiece only to find that, suddenly, it was sold out. 

[Jon Isaacs]

Today I purchased a "gently used" 2-inch, 30mm Ultima Edge Flat Field Eyepiece directly from Celestron's Website for a few pennies under U.S. $210 with free shipping.

 

 

 

Joe:

 

Congratulations on your new eyepiece.  It's a keeper..  Don is a treasure.  I bought my 30mm UFF from Don... 

 

Jon

[Joe Cepleur]

Thank you! Don has a startlingly detailed knowledge of all the quirks of seemingly every last eyepiece on the planet. Combining his help with everyone else's, I became convinced that I had to raise my modest price point to get something truly worth having. The goal was to compromise between being disciplined about minding my money now, and optimizing the unexpected gift of an unexpected, astonishingly fine 6" Jaegers refractor. My guess is that the sharpness and contrast will be about as good in this eyepiece as in more expensive eyepieces (at least to my eyes), with the only tradeoff being a 70⁰ apparent field instead of a larger one that would drive the price higher and that I do not (currently!) care about.

[Starman1]

The 28mm 82° UWA eyepiece in the same price range would be a decent choice too.

[sold in the US by Astronomics and Stellarvue.]

But, it is not glasses-compatible, and has a bit of edge of field aberrations.

Most find the aberrations ignorable, so it's mostly the higher weight and smaller eye relief that are its main negative points.

If the edge of the field correction is an important characteristic for you, the 30mm UFF is better corrected.

[sold in the US by Celestron dealers and Stellarvue.]

Edited by Starman1, 13 May 2025 - 09:20 AM.