EXCERPT page containing first few paragraphs. 2022-01-27 13:06:29
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Optical distortion is primarily barrel distortion (bowing outward) to the frame edges, then flattening to near-zero distortion to the corners.
Maximum distortion is held to 1.5%, which is outstanding for an f/1.4 design, and actually the world’s best in a fast 21mm as of 2015 (Leica 21mm f/1.4 Summilux-M ASPH has about 2.3% distortion). Indeed, the Sigma 20/1.4 has clearly superior distortion characteristics to the Leica 21mm f/3.4 Super-Elmar-M ASPH, which is 2.5 stops slower! It even beats the Zeiss Loxia 21mm f/2.8, and the Loxia is two stops slower.
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