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| p.1 #8 · ? minimum practical subject size vs image size for pro cameras |
Just out of curiosity Alan, have you checked EXIF data to see what focusing distance the lens is reporting? If I'm reading you correctly, I've seen some similar things from all sorts of camera and lens combinations, and it usually seems to manifest itself when most of the detail in the image is approximately the same distance away (and, I'm presuming from the EXIF data I've seen, the AF chooses to front focus for no apparent reason).
Not that it's definitive, but it might help you at least identify some patterns in AF behavior. I've often wondered if AF arrays can be influenced by interference patterns of complex subjects (branches in trees, for example, which we often assume to be a good, high contrast subject that AF 'should' be able to lock onto).
Regardless, I'm with you...