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Looking for Sharpness in all the Wrong Places

Field curvature can make a sharp lens soft in unexpected ways. Understanding how sharpness varies throughout the frame will help you get the most out of some excellent lenses that might not test well on flat (planar) test targets.

Related articles explore how diffraction and focus shift can lead to images with degraded contrast and resolution.

In the ideal world, a flat (planar) surface would be imaged onto a flat sensor, and a crisp image would result (a “flat field” lens). The real world doesn’t work that way for most lenses!

With most real lenses,  a desired plane of focus is actually imaged in sharp focus at varying distances from the nominal plane of focus, depending on distance from the optical center. Thus, portions of the image can be focused sharply in front of or behind the sensor, depending on location in the frame.

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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.


The corners in the background are just as sharp as the rice pounder at the center
Zeiss ZF 28/2 Distagon @ f/4 on Nikon D3

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