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Old Mar 14, 2004, 10:56 PM   #1
Join Date: Dec 2003
Posts: 98
Default Vignetting and eyepieces

Back again, to those who recognise me :-<

OK. I have a C750 camera. It has trouble with vignetting when I try to use it for digiscoping, even at full zoom, as close to the EP as I can get.

I thought of trying 2" eyepieces to vercome this.

However, I have noticed that my Nikon 9*25mm binocs, which have only a 13mm EP aperture diameter, give almost exactly the same vignetting as a standalone 26mm FL EP with a 25mm aperture diameter, when coupled with the 50-250 camera lens I was planning to use as a "scope".

The EP and the 50-250 camera lens give no vignetting when simply used as a scope.

Can somebody explain why this is happening?

Does this mean that using a 2" EP will simply not solve my problems?

Is there some particular property in even a 2" EP that I should be looking forthat will stop vignetting?

Thanks for any help.
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Old Mar 16, 2004, 8:25 AM   #2
Join Date: Mar 2004
Posts: 62

I ran across this URL. It is fairly detailed explanation of vigeting along with the math to back it up.


Understanding Vignetting while Digiscoping: Fundamental principles for matching eyepieces to cameras when coupling afocally.


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Old Mar 16, 2004, 8:41 PM   #3
Join Date: Dec 2003
Posts: 98

Thanks. I had been there. I will look again now that I understand a little more abot what I need and how it hangs together.
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Old Mar 16, 2004, 11:16 PM   #4
Join Date: Dec 2003
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hmmmm...it would appear that the overwhelming problem is the oly 750. All the calcs show I should walk it in, but the lens moves so far back when it zooms in, that this overcomes the narrowing field of view.

I know I have been told this :-< but I did not realise the seriousness of ths situation.

I think the reason the EP apertures make no difference is that at zoom, the lens is such a powerful influence that the EPs are of little account in the equation.

It is all a matter of being way out of the eye relief, and little to do with the EP dimaeter.
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