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Message: <blockquote data-quote="henry link" data-source="post: 1355937" data-attributes="member: 6806">Rather than trying to locate the close and distant points at which an image loses acceptable focus I've found that it is much easier to determine differences in DOF between two binoculars by using out of focus glitter points. There are many possible variations, but the basic idea is to focus both binoculars on the same sunlit object, then compare the size of defocused artificial stars (little shiny round things reflecting tiny images of the sun), which are placed far enough in front or behind the focused object so that the glitter point of the sun dissolves into a diffraction disc. The size of the disc indicates how much the glitter point is defocused, so larger discs = more out of focus = lower DOF. The eye's natural tendency to try to accommodate and judgements about acceptable sharpness are eliminated. Only the size of the disc matters. I should mention that only one eye should be used for this test and the diffraction discs should be carefully centered to occupy the same spot in the field as the original focused object. Low light tests can also be done with pinholes in aluminum foil stretched over a flashlight.BTW, very far out of focus glitter points have other interesting uses since they are images of either the exit pupil or the pupil of the eye, whichever is smaller. For instance, they can be used to measure how much of a binocular's objective is actually being used or observe how much off axis vignette is present.</blockquote>

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