EXCERPT page containing first few paragraphs. 2022-01-17 01:33:53
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Understanding field curvature behavior of a lens is key to extracting maximum image sharpness for any particular “shape” subject for that lens: choice of focus position can work for or against total image sharpness in a very substantial way. Stopping down is never a panacea, even with a 12mm lens.
See Making Sharp Images for a general discussion of field curvature.
What the MTF chart suggests
The MTF chart for the 12/2.8 Distagon shows that the edges and corners are less sharp than the central areas, particularly wide open. That said, these curves are among the best one might find for high-end 18mm (equiv) lenses. The difference between f/2.8 and f/5.6 is actually quite small most of the way to the edges— very high performance wide open.
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Diglloyd Guide to Mirrorless offers comprehensive integrated coverage of most APS-C and full frame mirrorless cameras and lenses.
Special emphasis is placed on Sony full-frame, including Sony lenses and the high performance Zeiss Batis and Zeiss Loxia lenses plus Rokinon/Samyang and others. Fujifilm X, Olympus and Panasonic M4/3, Sigma dp Merrill and dp/sd Quattro are also covered in depth. Years in the making, it offers a wealth of material for choosing and using a mirrorless camera.
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- Aperture series from wide open through stopped down, showing the full range of lens performance and bokeh.
- Optical quality analysis of field curvature, focus shift, sharpness, flare, distortion, and performance in the field.
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