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EXCERPT page containing first few paragraphs. 2023-02-04 06:46:59

Field Curvature with the Canon 16-35mm f/2.8L II

This example shows just how confusing field curvature can be.

In the image below, the left edge is soft, then the image sharpens and remains moderately sharp, then it goes very soft, then it sharpens again, then it becomes soft in the distance. Whew!

Where is our “plane of focus”?! The idea that sharpness is a geometric plane at a fixed focusing distance needs some serious rethinking. Sharpness is a zone. It can be a wavy zone that interacts with the subject in very confusing ways, as seen here.

It should also be clear that depth of field tables, hyperfocal distance, etc, are all rather simple-minded in the face of such behavior: focusing just a little differently can have a radical impact on sharp/unsharp.

A lens with wave field curvature is “unpredictable”, which makes it less desirable for many types of shooting. A flat-field lens, or one with a simple arc of curvature is better.

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  • 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.

Entire frame as shot
Canon 16-35mm f/2.8L II @ f/2.8

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