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EXCERPT page containing first few paragraphs. 2022-07-06 00:55:39

Color shading caused by extreme ray angle
Leica M9 + Zeiss ZM 21mm f/4.5 C-Biogon @ ~f/8

Ray Angle and Digital Sensors

For more details on the damaging effects of sensor cover glass on a digital sensor, see Astigmatism and Digital Sensors.

The ray angle is the angle of incidence to the sensor, generally given as the chief ray angle*, which is the central axis of a cone of light impacting a spot on the sensor.

As shown in the simplified diagram below, the bundle of light rays arriving at the focal plane has a cone shape with an angular spread; thus there are many rays arriving at the same location, but at different angles. With stopping down, the outer rays are cut off and what remains is thus a narrower and narrower cone of light with more and more stopping down.

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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.

Aspherical lens optical element showing ray bundle to focal plane
Image courtesy of Carl Zeiss Inc

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