Subject: | [OM] DoF Compared |
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From: | usher99@xxxxxxx |
Date: | Tue, 10 Aug 2010 18:47:34 -0400 |
"But if you tell me that you can *crisply* delineate focus at 5 meters vs. 5.5 or even 6 meters using live view I'll agree that the focusing part of my objection is moot. But that still leaves the performance of the lenses at f/4." Chuck Norcutt I think 10X live view on a tripod is about as accurate in focusing as one can get w/o a ton of bracketing and comparing like DXO does. A meter stick at a known angle at the focal plane might answer how much play is in the focusing. Mot sure how one separates performance per say from apparent or actual differences in dof. Some lenses as they are stopped down do not symmetrically add distance equally to the near limit and far limit of the dof (as "ideal" lenses do used in the usual geometric model calculations) ---some just add to the far limit. ?focus shift? This could happen with the same MTF performance. So a similar experiment looking into the near limit of dof could be evaluated with different findings. Aberrations in the lenses and color predominance of the scene could alter results too so it may be near impossible to dissect out "performance" differences in the lens from changes in perceived or real dof due to other lens design characteristics.. In any event I am impressed with AG---defined an interesting theoretical /practical issue, attempted a reasonable experimental approach to investigate, performed the experiment and then posted it (with crops even ) for our comments. Thanks. Mike -- _________________________________________________________________ Options: http://lists.thomasclausen.net/mailman/listinfo/olympus Archives: http://lists.thomasclausen.net/mailman/private/olympus/ Themed Olympus Photo Exhibition: http://www.tope.nl/ |
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