EXCERPT page containing first few paragraphs. 2023-03-29 14:46:41
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MTF for for ZM 85/4 Tele-Tessar
Wide open MTF is already at high levels, but with a dip in the middle (which might be a mild field curvature).
Stopping down to f/5.6 should deliver peak performance, with delivering a deeper zone of sharpness of f/5.6 with less risk of degradation from minor focusing errors, which are always possible given the f/4 maximum aperture.
The astigmatism seen at f/8 approaching the edges and into the corners might be traces of color fringing behavior (lateral chromatic aberration).
Like the 85/2 Sonnar, there is a small focus shift most visible from f/4 to f/5.6 and f/8 of about 40-50 microns (at the sensor plane), but it is better controlled than the focus shift of the Leica 90mm f/2 APO-Summicron.
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