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Criticality of Focus

This page establishes a baseline for understanding just how important focus accuracy is to exploiting the 24+ megapixels of the Nikon D3x. The goal is not any absolute metric, but rather simply to show that small focus differences (eg 1% of the subject distance) can produce subjectively quite different results, with high or lower contrast and more or less color fringing.

Resolution target

A resolution target was photographed at a distance of approximately 9 feet (2.7 meters) at a reproduction ratio of approximately 1:24. A tripod, mirror lockup and remote release were used on the D3x. Live View was used to focus wide open at f/2 on the Zeiss ZF 100mm f/2 Makro-Planar, zoomed in maximally for the best possible accuracy.

As seen below, the target shows some vignetting at f/2, and some uneven illumination (numerous Solux bulbs for near-daylight). We are concerned only with the center portion.

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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.


The well-used target. The strip of center patches is stacked, for “depth”.

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