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FAQ: Why are my Digital Images Sharper at f/8 than f/22?
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Aug 25, 2012 04:23:53   #
Nikonian72 Loc: Chico CA
 
This phenomenon is properly known as Small Aperture Diffraction, or circular aperture diffraction, or lens diffraction. This is a problem with digital photography through small apertures (usually noticeable at f/22). It is also a problem with all lasers. Associated terms: Airy's Disc, or Airy Disk, or circle of confusion. This phenomenon is strictly related to the relative size of an aperture in a lens, having nothing to do with the camera's sensor or film.

The following URLs contain diagrams, charts, and photo examples, which better explain and illustrate phenomenon:
http://www.cambridgeincolour.com/tutorials/diffraction-photography.htm
http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/cirapp.html
http://www.bobatkins.com/photography/technical/diffraction.html
http://www.luminous-landscape.com/tutorials/understanding-series/u-diffraction.shtml
http://en.wikipedia.org/wiki/Airy_disk

Because of this phenomenon, most serious macro-photographers routinely use apertures of f/11, or f/16, depending upon specific lens.
Note resolution drop-off on this chart of a world-class macro lens.

MTF (Resolution) for Nikkor AF 105mm 2.8 G
MTF (Resolution) for Nikkor AF 105mm 2.8 G...

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