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Distortion, Uncorrected and Corrected at Close Range
With an ultra high performance lens, low distortion is critical. That’s because correcting distortion can degrade micro contrast, which is a key part of “ultra high performance”. Thus if distortion correction is not needed, the lens can truly deliver outstanding performance that is unaltered and undamaged by correction.
The distortion graph from Sigma is for distortion at distance. The distortion at close range is considerably more, as this page shows.
Example, corrected vs uncorrected
This example at a reproduction ratio of about 1:5.5 is near MOD (minimum object distance).
Distortion at this distance is quite significant and requires a very significant “pixel stretch” which degrades micro contrast as the crops show. Real achievable sharpness is thus impaired for any application that needs accurate rendition: artwork or artifacts or copy work. Thus the performance which already badly lags the Zeiss 135mm f/2 APO-Sonnar at this range is further reduced.
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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.
- Make better images by learning how to get the best results right away.
- Save money by choosing the right lens for your needs the first time, particularly some of the new Sigma Art lenses vs Nikon and Canon.
- Workflow discusses image organization, raw conversion and post processing. Many examples show processing parameters for direct insight into how the image was converted.
- Jaw-dropping image quality found nowhere else utilizing Retina-grade images up to full camera resolution, plus large crops [past 2 years or so].
- Real world examples with insights found nowhere else. Make sharper images just by understanding lens behavior you won’t read about elsewhere.
- 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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