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Blur from Field Curvature

See also the full discussion on field curvature.

Head scratcher: image is sharp at center, blurry in the middle, and sharp at the edges. Huh? See the Case Study with the Canon 16-35mm f/2.8L II zoom.

The nominal plane of focus is imaged instead as a curve, which can be focused sharply in front of or behind the sensor, depending on where we look in the frame.

Field curvature can also alternate in front of or behind the nominal plane of focus, depending on distance from the optical center (wave-type field curvature).

In short, it’s a zone of focus, not a plane of focus.

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Diglloyd Making Sharp Images articulates years of best practices and how-to, painstakingly learned over a decade of camera and lens evaluation.

Save yourself those years of trial and error by jump-starting your photographic technical execution when making the image. The best lens or camera is handicapped if the photographer fails to master perfect shot discipline. High-resolution digital cameras are unforgiving of errors, at least if one wants the best possible results.

  • Eases into photographic challenges with an introductory section.
  • Covers aspects of digital sensor technology that relate to getting the best image quality.
  • Technique section discusses every aspect of making a sharp image handheld or on a tripod.
  • Depth of field and how to bypass depth of field limitations via focus stacking.
  • Optical aberrations: what they are, what they look like, and what to do about them.
  • MTF, field curvature, focus shift: insight into the limitations of lab tests and why imaging performance is far more complex than it appears.
  • Optical aberrations: what they are, what they look like, and what to do about them.
  • How to test a lens for a “bad sample”.

Intrigued? See Focusing Zeiss DSLR Lenses For Peak Performance, PART ONE: The Challenges, or (one topic of many) field curvature.

Test image at f/5.6

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