Originally posted by falconeye It is a bad idea to deduce the amount of front focus or backfocus from looking at some printed area outside the focus point. You can't know if your lens has a flat focus field.
+1
That's one of the points I make in my
AF adjustment hints.
I think the ideal target would provide an unambiguous perpendicular target for focusing and then (e.g., by a turning mechanism), at the very same spot, a tilted plane for the measurement of how big and in which direction the misfocus is.
Originally posted by falconeye More about this in a forthcoming paper I am writing as we speak
Looking forward to reading it.
Too bad that our Pentax cameras aren't programmable.
Even better, they could support the whole process with respective AF optimisation functionality.
Originally posted by falconeye In the above photo (even if turned into portrait) you see that the image center if far too close to the cluttered area.
I might be wrong but I thought the photo just shows the apparatus and wasn't a sample of using it. You are correct thought, incorrect attempts of making AF checks/adjustments are legion.
Regarding the distance to the target, doesn't it ultimately depend on which kind of situation (close focusing, infinity, general use) you want the best focus/compromise? I understand it is not always possible to get a setting that works best for all distances so my advice would not be to take a generic distance but think about in which situations focus would be most critical for one personally and than use a corresponding distance during adjustment. It may mean that one arrives at a setting that won't be useful/optimal for general use, though.