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Focus Shift with the 90/2 APO-Summicron-R ASPH (Dolls)
This pages shows the substantial focus shift at close range found with the Leica 90mm f/2 APO-Summicron-R ASPH. This is not a tutorial on the reasons for focus shift, for that see Making Sharp Images.
Background
In the course of testing the Canon 5D Mark III, I came across this behavior, which was at a distance of about 1.8 meters (6 feet).
I found that if I focused accurately at f/2, that stopping down did not deliver the sharp image I had hoped for. Experimentation showed that there was about a 2.5cm focus shift error from f/2 to f/5.6 being caused by focus shift— a massive shift in the zone of sharp focus.
The 2.5cm difference was determined not by refocusing the lens, but by using a nodal slider to millimeter-precise movement of the mounted camera. The actual difference might be slightly different but it also varies by aperture, the point being that it is a HUGE error at this distance.
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Diglloyd Guide to LEICA contains in-depth coverage of Leica M system cameras and lenses, with additional coverage of Leica M Monochrom, Leica Q.
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