Diglloyd article: Focus shift is a displacement of the sharp plane of focus when the lens is focused wide open, but the image is made with the lens stopped down.
This phenomenon has been showned as above in two cases in this threads, one at center and another at border of the lens. As explained at my earlier post, you will not see a focus shift from center of the lens (50L or any fat and short focal lenses) from a well calibrated lense at center point.
Click twice to simulate one during AF and other when aperture stopping down then flip flop between the two model windows to simulate your focus plane and light object plane shifting. This focus shift phenomenon is nothing more than an optical bending effects and some of our AF system can not keep up the light object plane shifting when the lens is stopping down.
Send your lens in for optical shift calibration if you noticed any blurry object at center when the lens was stopping down.
Nov 30, 2012 at 11:36 AM
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