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Message: <blockquote data-quote="jring" data-source="post: 3333540" data-attributes="member: 133897">Hi,I wasn't sure either if the photo rule of higher aperture number = small opening = high DOF is valid for binos, so I read it up in Holger Merlitz' book. He states that the depth of field in a binocular is only dependent on the magnification (actually the square of the magnification so it gets a lot smaller with higher magnifications). Objective diameter does not change depth of field - the limiting aperture here is the iris of your eye and the pupil size dependent on the lighting conditions. He also states that a high curvature of field in a bin might be perceived as lower depth of field since the center with the object you are looking at is sharp and and background objects toward the edge are shown blurred, but not due to a smaller depth of field but due to field curvature.Also the accomodation range of the eye varies between different persons and tends to get smaller with age, which obviously changes the perceived depth of field.Joachim</blockquote>