Emmanuel, nice tests. Hard to argue with practical results. You now have me wondering if I should purchase a few dedicated digital lenses for the 6x9 back.The conclusion is simple : when all lenses are stopped down to the same numerical aperture, namely we used f/11, the tolerance on film positioning, measured by reading the sharpness of test targets, is the same for all focal lengths stopped down at f//11, exactly as predicted by the geometrical model and the approx tolerance we derived from our tests matches perfectly the classical value of plus or minus N.c, no mystery.
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