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Message: <blockquote data-quote="typo" data-source="post: 3420903" data-attributes="member: 83808">Binastro,The psychologists spend a lot of time trying to find parameters to measure the factors that determin object detection and recognition but it's a sector of science I know nothing about and find largely incomprehensible. I've tried to read papers that relate observation duration and angular size as they relate to sharpness perception. It's a much faster temporal process and has an optimum at a much lower angular frequency than determination of acuity limit. I'd hazard a guess that it relates to the experience you are describing, but now you see it, now you don't, is a totally different parameter to seeing more detail with binocular than another, or on a stand or not which was the point I was addressing.On the question of whether there are better targets than the USAF chart. I have Snellen, Landolt C and Tumbling  E charts as well, and have tried on-line randomly generated tests (though they are very awkward to use at the distances required for binocular testing) and they all produce identical results, just as they should. These alternatives need more distance adjustment to deliver the accuracy of the line chart so are more of a pain to use.David</blockquote>