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Message: <blockquote data-quote="Surveyor" data-source="post: 3174517" data-attributes="member: 50720">Kimmo, Henry;I was looking at the last paragraph in my response to Kimmo and a thought jumped to mind. Not thought out and probably wrong, but I will do some checking when I have access to my notes again.The thought occurs to me that an empirical focus curve may be possible for average values of resolution versus defocus, something along the lines of (FACTOR*.01225-1.45=APPROX DEFOCUS i.e. 140*.01225-1.45=.26w or 200*.01225-1.45=1w or 250*.01225-1.45=1.6w.When I get the computer up and running again and some time, I will go through my MTF files and see how many I can put a resolution measurement to and see if I have a significant number and correlate well to do a curve function. This could be a useful figure for comparisons since it would be independent of actual hardware measurements. Also, I will start searching online; someone has probably already had this idea and may have done a large sample.Henry, if you have a chance, try this on some known scopes and see if gets even remotely in the ball park. If I can get a correlation above about .9 it may be worth the effort to do more sampling.</blockquote>