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Field Curvature and Focusing Distance

Field curvature varies with distance.

A lens might exhibit a flat field at close range, yet show strong field curvature near infinity. The Canon EF 14/2.8L II is one such lens, and even f/11 won’t overcome the field curvature at infinity focus. Yet another lens might exhibit a mostly flat field at infinity, but show substantial field curvature at close range—the Zeiss 25mm f/2.8 Distagon is one such lens.

These normal variations with distance often lead to erroneous conclusions about the merits of any given lens, especially in lab settings and “quick tests” (a “quick test” for a lens is almost an oxymoron).

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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.

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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.


  
Nikon 20mm f/3.5 AI-S center and corner, focus optimized for center

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