Focus shift ? Aren't all range finder lenses focused at the 'taking' aperture ? Certainly all my Leica M lenses are - focus shift is not a problem. Do you mean field curvature or are you saying that that the Sony 55/1.8 exhibits focus shift?
Focus shift. Rangefinder cameras don't take aperture into account when focusing. They can't...they have no idea what aperture you're using. It's a known issue with various M lenses when used on M cameras...there's a dip in performance in the f/4–5.6 range. This isn't because the lenses lose resolving power at these apertures, rather it's due to the point of focus having changed.
Keep in mind that the A7r's photosite count makes it easy to see this stuff. I've never noticed it with my X-E1, though I haven't gone looking for it either. (I've hardly used my 50s on the Fuji, prefering the Leitz 40/2 instead.) You have to
measurbate, something I normally avoid but which I indulged in here since I'm trying out some of my very favorite lenses. In practical use it's not a huge deal, but since eliminating the shift is easy with an EVF—just focus with the lens stopped down—you might as well do so. This turns an oft-maligned lens like the Leitz 50/2 Summar into a damned good performer. The lens is quite low in overall contrast (it's uncoated) but very high in resolving power, particularly in the center where it outperforms both of my Rigid 50/2 Summicrons and gives the Zeiss Planar a solid run for its money. My 1940s era Zeiss 50/1.5 Sonnar (Leica Thread Mount) also benefits in the f/2.8–5.6 range from this focusing technique.
The Sony/Zeiss 55mm does not exhibit focus shift. Nor does the M mount Planar.
Here's a lens that wasn't a surprise: the little 1970s era Leitz 90/2.8 Tele-Elmarit. Sharp & high-contrast at all apertures through f/11. Fits easily in a jacket pocket. A perfect short tele on the Sony cam, IMO.
-Dave-
