Circle of confusion: Difference between revisions

Revision as of 01:04, 26 October 2006

Revision as of 08:22, 26 October 2006

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format. For practical purposes, <var>d</var>/1730, a final-image CoC of

0.2&nbsp;mm, and <var>d</var>/1500 give very similar results.

Angular criteria for CoC have also been used. [[#CITEREFKodak1972|Kodak (1972)]]

recommended 2 minutes of arc (the [[Snellen chart|Snellen]] criterion of

30&nbsp;cycles/degree for normal vision) for critical viewing, giving CoC

&asymp;&nbsp;<math>f/1720</math>, where <math>f</math> is the lens focal

length. For a 50&nbsp;mm lens on full-frame 35&nbsp;format, this gave

CoC&nbsp;&asymp;&nbsp;0.0291&nbsp;mm. Angular criteria evidently assumed

that a final image would be viewed at &ldquo;perspective-correct&rdquo;

distance (i.e., the angle of view would be the same as that of the original

image):

:Viewing distance = focal length of taking lens &times; enlargement

However, images seldom are viewed at the &ldquo;correct&rdquo; distance;

the viewer usually doesn't know the the focal length of the taking lens,

and the &ldquo;correct&rdquo; distance may be uncomfortably short or

long. Consequently, angular criteria have generally given way to a CoC

fixed to the camera format.

The common values for CoC may not be applicable if reproduction or viewing