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Blur by Focus

Focus blur is due to the subject not being focused sharply.

Optical issues like field curvature and focus shift mean that areas of the frame away from the point of focus might not be focused, even if they are in the same subject plane. These subtleties do matter for getting and achieving the best results, even though it’s often first about user error (manual focus), or system error (autofocus).

Digital cameras are unforgiving of even tiny errors. Very small focus errors show a notable drop in MTF (contrast). There is no substitute for spot-on focus, not with high performance lenses. A world class lens becomes a quite ordinary one when the focusing ring is a fraction of a millimeter in error.

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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.

“Minor” focus error: how consistent is it?

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