Just published in DAP: study of focus shift with the Canon 50mm f/1.2L, 50mm f/1.4, 50mm f/1.8 II on the Canon 5D Mark III (in DAP). This follows my in-depth focus shift study of the Canon 50mm f/1.2L.
Why bother with studying focus shift? Because for many lenses, especially f/1.2, f/1.4, f/1.8 lenses, by far the most important lens parameter determining lens sharpness is focus shift.
Focus shift and what to do about it are discussed in detail in Making Sharp Images.
Nikon and other brand photographers should take the time to read this study, as there are plenty of Nikon (and Zeiss and Leica) lenses with focus shift.