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Message: <blockquote data-quote="Binastro" data-source="post: 3593643" data-attributes="member: 111403">Just read an old thread.Why wear glasses when using bins?3rd April 2006.It educated me more into understanding birdwatchers problems using glasses.I suppose that my eyes, at least one of them, is good enough to see birds well enough without glasses to go straight to using a binocular.I was going to ask what percentage of observers need glasses with binoculars, but it isn't that simple.Because people don't like continually taking specs off and back on.I found also via Sky an Telescope, Richard Buchroeder's formula, which I hope I can mention.Eyeglasses can be removed if astigmatism cylinder correction in diopters D for an exit pupil in millimetres is 1/square root D or smaller. Larger gives more than 1/4 wave of aberration.But I don't think binoculars meet these standards, as I can use larger exit pupils than the formula suggests.</blockquote>