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Message: <blockquote data-quote="Binastro" data-source="post: 3182660" data-attributes="member: 111403">. Thanks David.With one of your neutral density filters the brightness of Venus is reduced to the brightness of Jupiter, so I wouldn't expect much change.With three neutral density filters, i.e. 1/64 the brightness, Venus's brightness is reduced to the brightness of a first magnitude star, approximately the brightness of the four main stars in Orion. Rigel is brighter, but on average they are about right. That is a quite bright, but not very bright stars.So your findings are about what I would expect.. But I still don't know whether the binocular contributes to the enlarged image of Venus or whether it is only due to our eyes.Can you think of a test that does not involve our eyes, to determine whether the binocular itself increases the image size with a very bright point source or nearly point source object?Do spot diagrams take this matter into account?</blockquote>