P3D depth of field/ resolution - f/64

[John Toeppen <toeppen@xxxxxxxx>]

Bob Howard brought out some good points regarding photographic history
and the f/64 club.  The zone system Ansel's most important technical
contribution.

Due to focus limitations we often stop down to increase our depth of
field.  Stopping down also reduces the spherical abberation of most
lenses from 2 waves to a half wave or less.  At f/64 the spot size is
nearly diffraction limited but of a rather large size.  The size of a
diffraction limited spot is 2.44  x  the wavelenght  x  f#      Green
light is 0.5 microns, so, f/64 produces a 78 micron spot - a paper
thickness.  Panatomic X could resolve 400 lp/mm at 50% contrast - it
could resolve 70 micron spots at full contrast.

Ansel Adams was corrected by other knowledgable people.  By the 50s
Arthur Cox and others spread wrote texts like "Photographic Optics" and
filled them with useful tables and diagrams.  Holography depends on the
very principles that limit the performance of conventional photography -
the wave nature of light.  This was a comparitively recent
understanding.  Ansel did later admit that he was wrong at one time on
that point.  He was visiting the Nova Laser at the time.

Perhaps this is only important if it helps us realize that Ansel
produced great images with his heart and mind, not just his mind.

John Toeppen
new bee anaglyph on:
http://members.home.net/toeppen/index3.htm  

Nova laser:
http://vvc.llnl.gov/stereo/stereo.html  - bottom of page


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