a strange focuing issue

Started Jun 24, 2011 | Discussions thread
OP shonxiaohe Forum Member • Posts: 60
Re: Examples for Mark

I am a little confused by the term of "focus shift", my understanding of, e.g., "front focusing" is that, if you focus at a object at distance d, the picture show that the object at distance d-s is most clear, instead of the designated one at distance d.

therefore, wether F2 is shparer than F5.6 or not doesn't tell if there is a front focusing shift, neither the center is sharper than edge or not can tell, instead they may due to the lens' property, e.g., I notice from the MTF there is a strange drop for F4 at the edge, then go up again at the very edge range, or due to the un-even sensor installation etc.

on the other hand, the distance scale jumps to a closer number in the display might indicate a front-focusing if the number is correct. However, after checking the photo aganist a focusing test chart (or simply take a photo against a newspaper from a 45 degree angle), I would say, if there is a front focusing at F5.6, it is less than 1cm, which seems is much smaller than what the distance scale suggests, very strange and annoying, still...

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