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Progressive defocusing
Zeiss ZF 85/1.4 Planar@ f/1.4

Circle Of Confusion

The circle of confusion refers to the blur produced by an out-of-focus point of light. Usually discussed in theoretical terms, real blur circles are often misshapen or smeared.

The blur circle or circle of confusion (CoC) limits how much detail can be captured. A one-stop change alters the blur circle by √2 in diameter with each f-stop. The size of this CoC is the essence of depth of field.

While stopping down shrinks the CoC for improving depth of field, but it also tacks on diffraction effects which work to effectively enlarge the blur circle (simplification, see Huygens wavefront principle) with a reduction in contrast the main effect seen at first, followed by loss of resolving power into undifferentiated gray.

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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.

     

   
Figures S1 – S8: Progressive defocusing of Zeiss ZF 85/1.4 Planar@ f/1.4

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