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Testing for Focus Shift and Secondary Color

Detecting focus shift at close range (1:5 to 1:40 magnification) is straightforward. At greater distance, suitable targets are harder to find, but a landscape scene with level and uniform detail can work e.g., a gravel path or any scene with a central subject having good detail and with a fore/background. A good example of this can be seen in the Nikon 14-24mm case study.

Any target similar to the one shown at right will work for a close range test e.g., a ruler. High contrast black and white with regular lines or patterns are most useful, both for ease of focusing and analysis, as well as checking for secondary longitudinal chromatic aberration.

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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.

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