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Making Sharp Images: Case Study: Major Sharpness Gains via Ideal Focus with Lenses having Peripheral Forward Field Curvature (Pine Creek High Peaks)

There is little tolerance for focus errors on high resolution cameras (focusing along with field curvature and focus shift). The Sony A7R IV used here has 3.8 micron pixels, as does the Fujifilm GFX100 and the PhaseOne IQ4, all state of the art as of late 2019.

This page is critical reading for anyone shooting high-resolution digital using a lens having field curvature, in particular peripheral forward field curvature.

  • How focusing in the wrong place can means loss of many stops loss of sharpness across the frame. Here a 4.5 stop sharpness loss is seen in which f/4 is required to equal f/1.2 sharpness, and even f/8 still just shy of compensating for focus choice.
  • How focusing in the wrong place means that no amount of stopping down ever achieves the same peak quality.
  • How f/1.2 can deliver more total sharpness than f/2.8, via focus optimal for the particular lens in use.
  • Suggestions for assessing your particular lens, including what to do if a lens has asymmetry across the field (the norm).

While this series was shot with the Sigma 35mm f/1.2 DG DN Art, the findings here are of general use for photographers seeking to improve their skills, applying to any lens having peripheral forward field curvature, whether mirrorless or DSLR or medium format.

In Making Sharp Images:

Case Study: Major Sharpness Gains via Ideal Focus with Lenses having Peripheral Forward Field Curvature (Pine Creek High Peaks)

Includes specific findings and tips on how to greatly improve sharpness with lenses having peripheral forward field curvature.

f5.6 @ 1/320 sec electronic shutter, ISO 100; 2019-10-19 12:11:37
Sony A7R IV + Sigma 35mm f/1.2 DG DN Art + polarizer Breakthrough Photography X4
ENV: Pine Creek, altitude 8900 ft / 2713 m, 50°F / 10°C
RAW: LACA corrected, vignetting corrected
focus at far left

[low-res image for bot]

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