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Message: <blockquote data-quote="henry link" data-source="post: 1229773" data-attributes="member: 6806">Norm,The only optical problem I can imagine resulting from very close focus in binoculars that use moving eyepieces or moving objectives would be vignetting from a prism aperture. That could happen at close focus with a moving eyepiece or distant focus with a moving objective. I suppose spherical aberration will increase at very close focus, but I don't think that will be visible at binocular magnifications.As for binoculars that use moving focusing lenses like the Zeiss, I just don't know. Maybe somebody else has some ideas about that.Henry</blockquote>