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Olympus ZUIKO Auto-S 50mm f/1.2

Loss of Lens Brightness at Fast Apertures on a Digital Sensor

A “fast lens” as used here means f/1.4 on a full-frame camera, a “very fast” lens means f/1.2 or brighter, e.g., f/0.95

As of early 2014 there are no f/1.2 or faster lenses for a full frame camera that can deliver full effective lens speed. The reason is the wide angle of the cone of lighting hitting the sensor; a fast lens at full aperture has wide-angle cone of light and this light cannot be fully accepted by the sensor (acceptance angle and reflection). It is an aspect/variant of ray angle behavior.

For the reasons discussed in Ray Angle and Digital Sensors, very fast lenses have no speed (brightness) benefit over less fast lenses. On many if not most digital cameras, a lens faster than f/1.4 offers essentially no brightness recording benefit over an f1.4 lens until and unless sensor designs utilize a wider acceptance angle.

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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.

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