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DOF as a function of brightness

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Old Tuesday 17th May 2011, 01:32   #1
walternewton
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DOF as a function of brightness

In this review by Pete Dunne, he states that (all else being equal) a binocular that produces a brighter view will give greater depth of field than one with a dimmer view, since the brighter model will cause your pupil to constrict further (and that this is analagous to stopping down the aperture on a camera lens, which of course increases DOF.)

Agree? Disagree? Thoughts?
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Old Tuesday 17th May 2011, 01:51   #2
RJM
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Well a "bright" bino tends to be low powered too so I am skeptical about causality with his premise. It also implies the pupil constricts further from average ~2.5mm daytime dilation when the binocular is brought to the eyes. This would occur if the intensity of the light is changed by the binocular, but I do not think this is happening. If anything the shade of the eyecup might cause the pupil dilation to expand.
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Old Tuesday 17th May 2011, 02:02   #3
henry link
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That's a bit of trademark Pete Dunn nonsense.

Think about it. If an increase in binocular light transmission produced a precisely compensating decrease in pupil size then all binoculars, regardless of light transmission, would deliver the same amount of light to the retina and would all look equally bright. But, even if that happened the effect on DOF would be quite tiny. A 10% increase in light transmission would result in about a 5% compensating decrease in the diameter of the pupil which would change the focal ratio of the eye so little that the increase in DOF would be only a small fraction of a diopter. Long ago I concluded that Pete Dunne's writing on optics is best regarded as entertainment, not information

Last edited by henry link : Tuesday 17th May 2011 at 02:18.
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Old Tuesday 17th May 2011, 03:46   #4
walternewton
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Thanks guys for the replies.
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Old Tuesday 17th May 2011, 04:05   #5
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This thread will tell you pretty much everything about DOF, and also a bunch of stuff that will make your head explode.

http://www.birdforum.net/showthread.php?t=197575
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