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Message: <blockquote data-quote="henry link" data-source="post: 1530252" data-attributes="member: 6806">On the question of measuring pupil dilation with binoculars in front of the eye I've had good results using an out of focus artificial star. For sunlight measurements I set the binocular for infinity focus and examine a glitter point of the sun reflected in a Christmas tree ornament placed about 10' away. The out of focus disc is a pretty well focused image of the eye's pupil or the binocular exit pupil depending on which is smaller. For lower light situations I use a pinhole over a flashlight beam. Of course, at night actual stars can be used. Just now I made a crude measuring caliper from a piece of stiff wire and measured my pupils with two 8x30 binoculars in front of my eyes. I picked an old Zeiss 8x30B Porro with a 50 degree field and a Nikon 8x30 E II with a 70 degree field to test Jean-Charles very reasonable idea that a smaller apparent field might cause the pupil to open larger. Measurements were made by placing the wire just in front of the objectives and bending it into a "U" shape until the tips of the wire barely show at opposite edges of the image of the pupil. In sunlight I measured an effective aperture of about 18mm for both binoculars (18mm aperture= 2.25mm eye pupil). I could detect no significant difference. I used a flashlight with a pinhole placed in a deeply shaded area under some shrubs for a lower light measurement. The result was about 28mm for each binocular (3.5mm eye pupil). Once again the difference between the two binoculars was too close too call, but I had a slight impression that my pupil was a tiny bit larger looking through the Nikon, the opposite of what I would expect.BTW, this test is also useful for revealing how much off-axis vignetting is present at different light levels. Just move the disc toward the edge of the field to see the vignette.Henry</blockquote>

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