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I thought traditional focus shift was an optical phenomenon whereby you focus once (you can use center point), do not refocus for any subsequent shots, but just stop down and continue to shoot, you will see depth-of-field increase, but also shift. In some instances, I think dependent on distance to subject, the shift could cause your intended target to be outside the plane of sharp focus.
What you said ...works wells for an old film system where focus system and lens aperture can be controlled separately by the user. Our DSLR does not work that way. DLSR AF system performs it function while lens at wide open and our image sensor recording image right after the aperture stopping down. Below is a sample to illustrate the camera and lens sequence. Please, note the black square as our focus point.
Our AF focal plane stay the same where image focal plane has been flattered out by lens stepping down to f2.8. This DSLR focus shift phenomenon is a bit different than older film system
Edited on Nov 30, 2012 at 06:01 AM · View previous versions