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Detecting and Mitigating Focus Shift

To test a lens for focus shift, see the How To Test page (includes a video showing focus shift).

In general, if your lens is less sharp at f/4 than wide open, or hardly different, then you have focus shift! (This assumes you’ve shot both frames with identical focus e.g., on fixed manual focus).

Autofocus and by-eye focusing

As an example, the Canon autofocus system sees the image at effectively f/5.6. When the image is shot at a wider (brighter) aperture the focus ends up far forward of the intended area. When focusing by eye at f/1.2, but shooting stopped down, the focus moves behind the desired area.

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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.

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