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Cat’s Eye Effect

See also Bokeh — Aperture Blades.

The “cat’s eye” effect occurs at wide apertures because light entering at an oblique angle “sees” an ovalized shape instead of a circular one. Stopping down 1-2 stops is sufficient to eliminate this effect with most lenses, depending on lens design.

With a lens having a diaphragm that can be opened and closed manually while off the camera, hold the lens up to the light and look through the opening at a progressively greater angle. Or go outside at night and look through the viewfinder at point sources (defocus the lens) and/or use Live View in a corner 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.

Actual pictures of Zeiss 100mm f/2 Makro-Planar diaphragm— f/2, f/2.8, f/4, f/5.6, f/8

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