Jason_Brook wrote:
swifty168 wrote
Jason_Brook wrote
Dave, one thing to consider is that near MFD there is focus shift going on. Be sure to test and tune at multiple distances. A good rule of thumb is to stop down to f/1.8-2 near MFD. Thanks for the tip Jason.
Although I'm slightly confused though. Isn't focus shift the shift in focus plane between focusing (done with lens wide open) and when the aperture stops down if you selected a smaller aperture?
Or do you mean that the focus fine tune amount varies with distance, especially at MFD so stopping down helps to hide this with a deeper DOF? To me, and I may be wrong, focus shift is the plane of focus going out of tune between MFD/infinity; so yes, basically variable AF fine tune needed across distances.
Swifty's correct, focus shift is the change in focal point if the lens is stopped down. Phase detect AF does its thing with the aperture wide open, but if you've selected a stopped down aperture, the focus will shift due to spherical aberrations when the shutter is released.
Stopping down closer to MFD is just good photographic practice with a lens with such a thin DOF, but ironically, closer distances is when focus shift is most noticeable.