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EXCERPT page containing first few paragraphs. 2022-05-24 11:07:08

Astigmatism and Digital Sensors

See the discussion of optical astigmatism as well as astigmatism and lateral chromatic aberration.

Sensor cover glass

Digital sensors always have a cover glass layer (excepting certain specially modified cameras). Brands and models vary in the thickness of this sensor cover glass (aka “filter plate”). The glass servers several functions; it protects the sensor itself, incorporates an infrared-blocking glass, and it often incorporates an optical low pass filter.

In general, the sensor cover glass is responsible for reducing lens performance because it also refracts light. Optical designs can compensate to some degree if the thickness is known, but if a design is to be applied to more than one brand or even different models within a brand, the thickness can vary. Hence fixed lens cameras have an inherent advantage of being able to compute the optical design for a known sensor design.

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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.

Double image caused by sensor cover glass filter accentuating astigmatism

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