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One kind of test target

Testing and Adjusting Autofocus Accuracy

Distinct from testing a lens for its optical quality is testing it for its autofocus accuracy on a particular camera body. Testing for optical quality should never be done using autofocus. But accurate autofocus allows the optical quality to be exploited.

Things to be aware of before testing autofocus accuracy

Focus is camera + lens specific

The same lens might behave differently on each camera body, so don’t assume that if a lens needs a +5 adjustment on one body that it will also need the same adjustment (or any adjustment) on another body.

If the camera is consistent about its error, then you’re in luck: make the adjustment so that the focus is spot-on. If the camera is not consistent, try another target to cross-check, then make the adjustment that produces the best average result.

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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.

Canon 5D Mark II fine focus adjust.

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