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Aperture series 2.8, 5.6, 8, 11, 16, 22 available in full article
Depiction of Airy disc

Influence of Pixel Size

When rays of light pass through an opening (e.g., a lens diaphragm), they form a wavefront interference pattern know as the Airy disc (Huygens-Fresnel principle).

The Airy pattern with all of its rings has an identical shape for any perfect lens with a round aperture. The only thing that changes with stopping down is the size of the Airy pattern, scaling linearly with the f-stop. This assumes a perfect aberration-free lens.

As the hole (lens diaphragm) becomes smaller (“stopping down”), the scattering effect increases; this causes a drop in contrast. At the same time, the Airy disc steadily becomes larger, with its diameter placing a fixed limit on resolution at any given aperture.

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  • 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”.

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Depiction of Airy disc size relative to photosite size for apertures f/2.8, f/5.6, f/8, f/11, f/16 and f/22.
Note how the Airy disc begins to cover more than one photosite at apertures f/8 and smaller.
The diffraction limit is reached when two Airy discs overlap by half their diameter.

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