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Sigma 120-300mm f/2.8 DG OS HSM S

Symmetry Across the Frame

Even the very best lenses can show asymmetries and these can change with minor focus differences: as elements rotate with focusing (or zooming), maintaining perfect symmetry is an elusive goal and perfection is likely reserved for cine lenses.

Very few lenses can achieve perfection on such a test and sample variation makes any conclusion about a lens design inappropriate. All that can really be said is that a particular examples has this or that weakness (at this or that focal length and focusing distance).

See for example, the Leica 180mm f/3.5 APO-Elmar-S cxample, noting that is is a expensive high-end prime lens with an asymmetry. If such lenses have symmetry weaknesses, how can we expect a varifocal lens costing half as much to be perfect?

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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.

f/2.8 @ 354 seconds, ISO 100 +1.0 push
Canon 5D Mark III + Sigma 120-300mm f/2.8 DG OS HSM S

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