Isn't the definition talking about the "entrance pupil", which is the image of the aperture in front of the lens ? So you have to determine the diameter of the aperture image, and not of the aperture itself ?
Beats me....
Back when I used manual flash for macro I delved the concept of pupillary magnification (ratio of the exit pupil to entrance pupil) and the effect that has on the exposure increase factors relative to extension - but AFAIK the very concept of entrance pupil / exit pupil is a function of asymmetric lens design. I don't think it has anything to do with the basic definition of f-stops or with the physical size of the aperture.
In my case, the lenses I used were fairly symmetrical and other factors - like the angle of the flash to the subject - had far more impact on the accuracy of exposure. So I did not spend much time dwelling on pupillary magnification.
- MCC
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Mark Cassino
Kalamazoo, MI
[EMAIL PROTECTED]
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Photos:
http://www.markcassino.com
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