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EXCERPT page containing first few paragraphs. 2023-03-25 03:53:25

Canon EOS 5DS R
Sigma 20mm f/1.4 DG HSM A

Field Curvature

This medium distance scene assesses field curvature, with clear-cut definitive results.

All wide angle designs of f/2.8 or faster speed of all brands have significant to substantial field curvature. Field curvature results from the natural Petzval field curvature inherent to lenses.

With an f/1.4 design, balancing field curvature against other aberrations is quite difficult. This is why wide angle lenses are just never free of some field curvature, particular f/1.4 and f/2.8 designs, but even f/2.8 designs still exhibit some field curvature.

Example — fence

Here the focus was at center on the broken section of the fence. One would therefore hope to see a sharp image across that plane, with nearly sharp imagery along the rest of the fence. But it is not so.

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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.

Want a preview? Click on any page below to see an excerpt as well as extensive blog coverage, for example on Nikon or on Canon or on Pentax.

Aperture series 1.4,2,2.8,4.5 available in full article

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