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Message: <blockquote data-quote="OPTIC_NUT" data-source="post: 3148610" data-attributes="member: 121951">Some 'ballpark' figures:---human acuity (well illuminated) is usually around 60 arc-seconds---30 arc-seconds is rare but has happenedSo, 10-power with 6 arc-seconds actual (60 apparent) resolution would be the limit for most people   (as far as what the thing has to do)3 arc-seconds actual would be the point past which no-one can tell.That said, I have seen airplane details lower than that myself.I'm guessing larger detail can actually be guessed at to finer detail than point seperation,   assuming the cortex is doing a sort of line-fit or curve-fit.If you want to see if the instrument resolves finer than your eye can use, use a statictarget, mount, and a low-powered monocular at the eyepiece. I found a 6x does OK,though a 2x or 4x multiplier is brighter and less fussy.</blockquote>