Telescope Reviews: Small Binoculars - Illumination of the Exit Pupil

This is a test I developed several years ago that measures the light distribution within the exit pupil from points entering at various measured positions on the objective lens. This gives an indication of the overall Illumination of the Exit Pupil. While many people argue that total aperture and especially the diameter of exit pupil controls the brightness comparison of one binocular to the other, few if any ever test for total illumination within the exit pupil. They simply assume that one exit pupil is just as equally illuminated by the entire objective as every other exit pupil and that exit pupil size determines brightness. That is not so. For instance, we sometimes hear an avid user exclaim 'my 4mm exit pupil model is so much brighter than that 5mm exit pupil model.' But few ever perform this type of test to find out if so, then why so. I've been performing this test on various models for years and, to say the least, it provides some "illuminating" information.

First let me say, I will not expend the effort here again to explain how to do this test or how it works. That has all been done, exhaustively, and the information is all documented in the "Best Of" links. There have been hundreds of posts and thousands upon thousands of words written both criticizing and defending the method and the validity of this test. There have been several who have vehemently denied it as valid. However, there are just as many who understand it and stand behind this test. For my part, I had some detailed discussions with Roland Christen, president of Astro Physics, foremost among numerous other very knowledgable individuals here on CN, explaining my method and gathering comments in support of the validity of this method of testing.

So as I gather the data I will post the results in this thread in the various groups. The first group (in the next post) is results for the 8 x 32/40/42 porros.

Further reading
Brightness in Exit Pupil
is not always just a simple funtion of the size of the exit pupil

from the discussion in the above thread:

Vignette. it is present in almost all systems. The more vignette in the system, the more non-uniform will be the brightness. While central brightness may be equal out to 30 or 40 or even 50%, the outer area will always differ.

Remember the discussions of vignette with the laser test showing the cutoff of exit pupil. That shows the nonuniformity of the light distribution in the exit pupil.
Exit Pupil Profile of Oberwerk Ultra 15x70, Fujinon FMT-SX 16x70 and Garrett Gemini 20x80

Exit Pupil Profile of Nikon SE 12x50, Fujinon FMT-SX 10x70 and Oberwerk LER 15x70.

Also see the Best Of thread
ABERRATIONS AND DEFICIENCIES
for links to the above descibed epic discussion on Vignette

VIGNETTE
Vignette, or the blocking of light, by whatever means, reduces the amount of light delivered by the optical system before it eventually reaches the receptor which in this case is your eyes. There are several different deficiencies that could be causing vignette. Identifying what is causing it is more difficult than identifying how much of a light loss is present.

edz

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