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Message: <blockquote data-quote="henry link" data-source="post: 3148878" data-attributes="member: 6806">Lee,When the AFOV is increased from say 60º to 70º the off-axis rays between 60º and 70º that were blocked by the eyepiece field stop are uncovered. ALL of that "extra" light goes into  forming an image in the extra 10º along the outside edge of the field. None of it "reinforces" the light falling within the original 60º. Perhaps a non-binocular analogy might make it clearer. Imagine projecting a photo onto a 70" screen. Now substitute a 60" screen at the same distance. The outer 10" of the photo no longer fall on the screen, but nothing changes about the brightness in the part of the photo that continues to fall on the smaller screen.Oddly enough, exactly the opposite relationship between AFOV and brightness has also been aired here. The idea is that a wider AFOV might project enough extra light into the eye from the outer part of the field to cause the eye's pupil to contract, thus dimming the entire field.Henry</blockquote>