EXCERPT page containing first few paragraphs. 2024-04-16 12:01:55
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MTF for Nikon 20mm f/1.8G
MTF is provided only for f/1.8 (wide open).
Central contrast is superb wide open, but it rolls off strongly and evenly to the corners to where it is modest at best. Still, the MTF for f/1.8 is quite good in theory, yet these are computed numbers which might or might not be reflect reality for a real lens using measured numbers white light (as is the practice as Zeiss).
The graph cannot tell us if the steady drop-off in contrast from center to corners is a field curvature, or simply reduced lens performance from other aberrations.
Astigmatism probably increases with stopping down (as other aberrations diminish and reveal it even more clearly), a theory supported by the evidence of observing substantial color fringing (lateral chromatic aberration) on some field subjects.
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Diglloyd DAP is DSLR-oriented, but also contains workflow and other topics. Much of the focus is on Canon and Nikon but also Pentax and Pentax medium format.
Special emphasis is placed on lens evaluation, focusing on Canon and Nikon and Sigma lenses, but with a few others like Rokinon/Samyang.
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