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DOF as a function of brightness (1 Viewer)

walternewton

Well-known member
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?
 
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.
 
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
 
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