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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. It is usually discussed in theoretical terms, which has little bearing on what a real blur circle made by a real lens looks like at wide apertures.

Wide open, lens barrel vignetting causes a partial eclipse of the blur circle (the “cat’s eye” effect). It’s one reason why off-center detail can be sharper than expected— the blur “circle” is smaller than at center because the aperture is smaller in area; this increases depth of field just as any smaller aperture does (the shape is not relevant, only the area).

In addition, lens aberrations of many kinds render points of light as shapes that bear little resemblance in color or shape to the original point of light.

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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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