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Blur by Autofocus Error

Autofocus is generally very good to excellent on most cameras under most conditions, and also generally better than most people could possibly focus by eye, especially in lower light conditions.

But with higher resolution digital cameras and particularly with fast lenses (e.g., f/1.2 or f/1.4 or even f/2), phase-detect autofocus systems show limited precision, which is often described as an accuracy issue, which might or might not be true (assuming system tolerances are to specification). The newer and more advanced on-sensor contrast-detect autofocus systems show great promise in supplanting phase-detect system.

Moreover, autofocus is subject to certain tolerances which together can result in image sharpness that is substantially less than what the camera’s sensor is capable of recording. Even a camera and lens “within specification” can produce unsatisfactory results, so test your camera and verify its accuracy with each lens. See How to Test a Lens— Autofocus Accuracy as well as the case study with the Leica S2 and case study with the Nikon 24mm f/1.4G.

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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.

Variants Autofocus, Manual Focus available in full article

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