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Another Leica zoom question...

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#26 gnowellsct

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Posted 22 November 2021 - 09:38 AM


Leica suffers from a little EOFB in a telescope, but the field of view and the optical quality are better than the Baader astronomical zoom, IMHO.

Cheers,

Ron


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#27 gnowellsct

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Posted 22 November 2021 - 09:45 AM

I think the eofb is a retinal artifact from rapidly and smoothly changing from one magnification to the other. At high magnification you're staring at a black field that is typical background sky of a magnified view. When you go to lower power the dark field you were just looking at is now centered as an afterimage in the brighter new lower power field.

To me it seems like it goes away after a while suggesting it is not in the eyepiece as such but an effect that is associated with using it.

If you switch from a Pentax 7 to a Pentax 14 you don't get a similar effect because you're not changing apparent field of view.

Owners of the Leica zoom might want to check this theory out by observing at 9 mm and then zipping up to 16 and then putting the thing away for an hour while you observe with other stuff and then coming back and seeing if the effect is still present.
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#28 RAKing

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Posted 22 November 2021 - 09:56 AM

I think the eofb is a retinal artifact from rapidly and smoothly changing from one magnification to the other. At high magnification you're staring at a black field that is typical background sky of a magnified view. When you go to lower power the dark field you were just looking at is now centered as an afterimage in the brighter new lower power field.

To me it seems like it goes away after a while suggesting it is not in the eyepiece as such but an effect that is associated with using it.

If you switch from a Pentax 7 to a Pentax 14 you don't get a similar effect because you're not changing apparent field of view.

Owners of the Leica zoom might want to check this theory out by observing at 9 mm and then zipping up to 16 and then putting the thing away for an hour while you observe with other stuff and then coming back and seeing if the effect is still present.

I have noticed this effect many times and it does seem to go away, leaving me to wonder if I really saw what I think I saw.

 

I am not a doctor, nor did I ever play one on TV, but I can say the EOFB never bothered me enough to trash my Leica zoom.  I had other things that bothered me, but I knew for sure they were related to my eyes and not to the equipment.

 

Cheers,

 

Ron


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#29 areyoukiddingme

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Posted 22 November 2021 - 01:48 PM

The EOFB also has been attributed to sky conditions, particularly transparency. The effect seems to show up some nights and not others.

 

It would be interesting to find out if it's just the zoom process. But I suspect it's not, as I'd expect EOFB concerns to show up more consistently for zooms as a group.


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#30 gnowellsct

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Posted 22 November 2021 - 04:23 PM

The EOFB also has been attributed to sky conditions, particularly transparency. The effect seems to show up some nights and not others.

 

It would be interesting to find out if it's just the zoom process. But I suspect it's not, as I'd expect EOFB concerns to show up more consistently for zooms as a group.

That might depend on the change in AFOV from low to high mag within the zoom.  I havne't played with many zooms...

 

 

Greg N


Edited by gnowellsct, 22 November 2021 - 04:34 PM.


#31 Sarkikos

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Posted 24 November 2021 - 09:16 AM

Most of the "trashing" I have heard over the years is regarding the cost.  Maybe some people in astronomy aren't as familiar with the Leica brand as those of us in photography or medicine.  I spent many years in photojournalism and Leica was one of the top brands in still photography.  Many (Most?) of us switched to Canon in the digital age, but I have a few Nikons from my 35mm film days and still fondly remember my old Leica M4.  They were expensive back then and they are expensive now.  smile.gif  

 

Leica suffers from a little EOFB in a telescope, but the field of view and the optical quality are better than the Baader astronomical zoom, IMHO.

 

Cheers,

 

Ron

I will take a little EOFB which appears sometimes in the Leica, over a lack of parfocality which appears almost always in the Baader Zooms and other zooms.  I'm not even considering the AFOV in this comparison.

 

The Leica Zooms are perfectly parfocal or very close to it, i.e., someone with poor focus accommodation - like myself - will likely not need to refocus when going from the high-power setting to the low-power setting.  

 

The Baader Zooms are not parfocal.  I need to refocus when using them.  The Mark IV is even less parfocal than the Mark III.  I've found that the Baader Zooms appear more parfocal with a Barlow and with slower telescopes, often to the point of appearing perfectly parfocal.

 

Probably observers who observe with slower telescopes, such as Maks or SCTs or long focus refractors, might not ever notice the nonparfocality in the Baader Zooms, even if their eyes have lost accommodation for focus.

 

Mike


Edited by Sarkikos, 24 November 2021 - 09:26 AM.

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#32 Sarkikos

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Posted 24 November 2021 - 09:19 AM

The EOFB also has been attributed to sky conditions, particularly transparency. The effect seems to show up some nights and not others.

 

It would be interesting to find out if it's just the zoom process. But I suspect it's not, as I'd expect EOFB concerns to show up more consistently for zooms as a group.

No, in my experience the EOFB in the Leica is not due to the zoom process.  I have seen that the EOFB is more obvious under poor transparency.

 

Mike



#33 Sarkikos

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Posted 24 November 2021 - 09:24 AM

I think the eofb is a retinal artifact from rapidly and smoothly changing from one magnification to the other. At high magnification you're staring at a black field that is typical background sky of a magnified view. When you go to lower power the dark field you were just looking at is now centered as an afterimage in the brighter new lower power field.

To me it seems like it goes away after a while suggesting it is not in the eyepiece as such but an effect that is associated with using it.

If you switch from a Pentax 7 to a Pentax 14 you don't get a similar effect because you're not changing apparent field of view.

Owners of the Leica zoom might want to check this theory out by observing at 9 mm and then zipping up to 16 and then putting the thing away for an hour while you observe with other stuff and then coming back and seeing if the effect is still present.

No, not according to my experience.  In the Leica Zoom, if EOFB is going to show on a particular night, it will show in the Leica as soon as I look through it.  I don't have to zoom the Leica to see the EOFB.  The EOFB has nothing to do with zooming.

 

The EOFB is more obvious under poor transparency.  I suspect that observers who have a Leica Zoom and don't notice the EOFB are lucky enough to observe in areas with consistently good transparency.

 

Mike



#34 Sarkikos

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Posted 24 November 2021 - 09:35 AM

I can't say that I've felt cramped when viewing at the lower power with a Leica Zoom. The narrower field of view is about 60 degrees. (It's 42 degrees in the Baader Zoom.)  No one ever used a 20mm Plossl or Ortho?  They are even narrower than the Leica.  And remember that the Delite AFOV is only 62 degrees.  Most objects in many telescopes will fit very comfortably in that field of view.  The only times I've felt compelled to switch to a wider field of view eyepiece is when viewing wider objects, or when I want to view at a lower power.  Otherwise I opt for convenience and leave the Leica Zoom in the focuser.

 

I use all settings of the Leica Zoom, from high to low.  I always thought it was more than a little silly to switch to another eyepiece with a wider AFOV instead of just keeping the Leica Zoom in the focuser.  Now if you want a lower power, that's something different.  For my typical minimal set, I'll bring out the Leica Zoom, 30mm APM UFF, 7 Delite, and 3-6 Nagler Zoom.  The 30mm APM UFF has a 70 degree AFOV.

 

Mike


Edited by Sarkikos, 24 November 2021 - 09:56 AM.


#35 StarAlert

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Posted 24 November 2021 - 09:39 AM

What? I thought it had a 60o AFOV at the low-power end. 


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#36 Sarkikos

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Posted 24 November 2021 - 09:42 AM

What? I thought it had a 60o AFOV at the low-power end. 

Yes, you are correct.  I must have been thinking about the Baader Zoom's AFOVs.  The AFOVs I have for the Leica Zoom are 81-59.  The AFOVs for Baader Zooms are 72-42.  I have corrected my post.

 

Mike


Edited by Sarkikos, 24 November 2021 - 09:44 AM.

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#37 RAKing

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Posted 24 November 2021 - 09:48 AM

That's just a minor "senior moment".  lol.gif

 

The 60-degrees of the Leica compares quite nicely with the view of a Radian or DeLite and a lot of people like that narrower view.  I use my Leica to fill the high magnification side of my scopes and have never felt cheated by a 60-degree FOV.

 

Ron


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#38 Sarkikos

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Posted 24 November 2021 - 09:53 AM

That's just a minor "senior moment".  lol.gif

 

Ron

No, I chalk it up to low blood sugar.  I haven't eaten breakfast yet. wink.gif

 

But do you notice how super quick the response was when I said the Leica Zoom's AFOV was only 42 degrees at the low-power setting?  That's saying something about the priorities now.  I almost cheated them out of 22 degrees!  lol.gif  

 

Mike


Edited by Sarkikos, 24 November 2021 - 09:54 AM.

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#39 RAKing

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Posted 24 November 2021 - 09:55 AM

I saw it too, but decided to give you a few minutes to correct it before I jumped in. flowerred.gif

 

The correct number is 18 degrees of difference!

 

Cheers,

 

Ron


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#40 Sarkikos

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Posted 24 November 2021 - 10:01 AM

Now, even I would object to 18 degrees!  That sounds worse than a Huygens or a Supermono!

 

Mike


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#41 Sarkikos

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Posted 24 November 2021 - 11:58 AM

I'm looking into figuring out a minimalist set involving only zoom eyepieces and Barlows.  When the new APM zoom with constant 75-degree AFOV comes out, we'll have even more options.

 

Mike



#42 payner

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Posted 24 November 2021 - 12:03 PM

The EOFB is more obvious under poor transparency.  I suspect that observers who have a Leica Zoom and don't notice the EOFB are lucky enough to observe in areas with consistently good transparency.

 

Why is it seen in poor transparency? I almost always saw the EOFB in the Leica (I often have 4/5 seeing, sometimes better, with poor transparency, though winter can bring excellent transparency and less optimal seeing), but I do not see it under same conditions in my fixed focal length eyepiece.


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#43 Sarkikos

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Posted 24 November 2021 - 12:07 PM

The EOFB is more obvious under poor transparency.  I suspect that observers who have a Leica Zoom and don't notice the EOFB are lucky enough to observe in areas with consistently good transparency.

 

Why is it seen in poor transparency? I almost always saw the EOFB in the Leica (I often have 4/5 seeing, sometimes better, with poor transparency, though winter can bring excellent transparency and less optimal seeing), but I do not see it under same conditions in my fixed focal length eyepiece.

Good question.  I'm not sure if anyone has explained exactly why EOFB is more obvious in the Leica under poor transparency.  But the lack of an explanation for a phenomenon does not negate the existence of the phenomenon, although some seem to think that is the case.  wink.gif

 

Mike


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#44 payner

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Posted 24 November 2021 - 12:55 PM

Agree and my question was more rhetorical in nature. I've seen the question bantered around (an awfully lot), but no definitive reason. I see it as an eyepiece designed for daytime, spotting scope use, so not surprising it is not at its optimal when used for astronomy. That comment was not to detract from those positive qualities often found by users for that application.


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#45 Jeff Morgan

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Posted 24 November 2021 - 01:34 PM

The 60-degrees of the Leica compares quite nicely with the view of a Radian or DeLite and a lot of people like that narrower view.  I use my Leica to fill the high magnification side of my scopes and have never felt cheated by a 60-degree FOV.

 

And in my case I really don't spend much time at the lowest power 60 degree AFOV setting. I'm usually turning up the power right away. The "narrow" field (and tiny bit of vignetting) is gone at the slightest advance of the zoom ring.

 

As you point out the 62 degree DeLite is a huge seller. And those owners are "stuck" with 62 degrees 100% of the time.

 

Obviously, this class of AFOV is not too onerous a burden to live through.


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#46 Jeff Morgan

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Posted 24 November 2021 - 01:45 PM

Agree and my question was more rhetorical in nature. I've seen the question bantered around (an awfully lot), but no definitive reason. I see it as an eyepiece designed for daytime, spotting scope use, so not surprising it is not at its optimal when used for astronomy. That comment was not to detract from those positive qualities often found by users for that application.

 

Generally, that revolves around how distortion is handled. Rectilinear vs Angular Magnification. It comes into play for manual tracking and is more of a personal preference than a performance issue.

 

All of my mounts use drives, so the importance of RD vs. AMD for me is exactly:

 

https://www.youtube....h?v=2V3CfD8TPac

 

Make the earth's rotation stop and everything gets better.


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#47 areyoukiddingme

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Posted 24 November 2021 - 02:11 PM

No, not according to my experience.  In the Leica Zoom, if EOFB is going to show on a particular night, it will show in the Leica as soon as I look through it.  I don't have to zoom the Leica to see the EOFB.  The EOFB has nothing to do with zooming.

 

The EOFB is more obvious under poor transparency.  I suspect that observers who have a Leica Zoom and don't notice the EOFB are lucky enough to observe in areas with consistently good transparency.

 

Mike

My recollection is also that I see the EOFB prior to zooming, but now that I know it is there, I do tend to notice the effect is often amplified by zooming. So there may be some interaction going on.

 

At this point, I think my expectations are also starting to play a role. There are also nights where I've seen EOFB in my XWs too, again consistent with your observation regarding sky conditions.


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#48 payner

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Posted 24 November 2021 - 02:27 PM

Generally, that revolves around how distortion is handled. Rectilinear vs Angular Magnification. It comes into play for manual tracking and is more of a personal preference than a performance issue.

 

All of my mounts use drives, so the importance of RD vs. AMD for me is exactly:

 

https://www.youtube....h?v=2V3CfD8TPac

 

Make the earth's rotation stop and everything gets better.

My point was relative to EOFB, not RD or |AMD. See posts 42 & 43 for the context.



#49 payner

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Posted 24 November 2021 - 02:47 PM

BTW, for what it matters, all of my mounts "make the earth's rotation stop ...". Yeah, it's a preference of mine, too.


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#50 Sarkikos

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Posted 24 November 2021 - 05:34 PM

My recollection is also that I see the EOFB prior to zooming, but now that I know it is there, I do tend to notice the effect is often amplified by zooming. So there may be some interaction going on.

 

At this point, I think my expectations are also starting to play a role. There are also nights where I've seen EOFB in my XWs too, again consistent with your observation regarding sky conditions.

Pay attention to whether the EOFB appears more obvious at low power or at high power.  If this is the case, it's appearance or severity might be affected by exit pupil, rather than the act of zooming itself.

 

When I first acquired a Leica Zoom, I recall comparing it with my set of XW's.  On nights of poor transparency, the XW's would show slight EOFB, while it was much more apparent in the Leica.  The transparency had to be excellent for me not to see any EOFB in the Leica.  That doesn't happen very often around here. 

 

Mike


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