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I've noticed that several online and/or downloadable Depth of Field Calculators use different values for the acceptable CoC (Circle of Confusion) for some of the same camera models/sensor sizes. This, of course, leads to different DoF (Depth of Field) results when any particular lens and aperture are entered. Below the rest of this question is a quote from Russel McMahon's answer to this question: Analysis of a macro shot with very fast shutter speed

Since the acceptable CoC entered in the formulas affects the DoF calculated, what criteria is used to determine acceptable CoC? The two numbers (0.029mm for Full Frame and 0.018mm for APS-C) listed in the Wikipedia article for CoC seem to be based on a set viewing distance and print size. Several of the online DoF calculators use different CoC values for cameras with sensors the same size as the FF and APS-C used in the Wikipedia CoC article. Wouldn't the acceptable CoC change for prints of different sizes from the same size image or a web displayed image at varying screen sizes/resolutions? How would you calculate an acceptable CoC for a given veiwing size and distance?

DOF

f = focal length
N = Aperture f number
c = circle of confusion
s = subject distance (assumed >> f)

DoF Formula

from Wikipedia DOF

c ~= 0.025mm for FF 35mm.
c ~= 0.018mm typical crop APSC.

see Wikipedia COC


Some more DOF calculators ..... agh

Many provide hyperfocal distance as well.

Bob Atkins - useful discussion and a useful tabular output calculator.

Cambridge

DP Review

Canon

Outsight

5+5+5 DOF calculators + other toys

AppBrain

itunes !!!!!!!!!!

Dyxum - whyt not, eveybody else does :-)

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1 Answer 1

up vote 4 down vote accepted

The acceptable CoC depends on the point at which increases in resolution yield only a marginal increase is perceived detail. This in turn depends on your eyesight, distance from the media and properties of the media in question.

You can either determine this value yourself, or accept a figure that Zeiss (supposedly) came up with decades ago and divide the diagonal of your print size by 1730. Most do the latter.

One final note, the acceptable CoC for web sized shots is huge, so much so it renders DoF calculations almost redundant.

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1730 divided into a full frame diagonal 43mm yields .025mm. But the same print size from a 26.8mm diagonal Canon APS-C sensor would need a CoC of .0155. At d/1500 instead of d/1730 the numbers are .029 & .018 respectively. Each variation of the Zeiss formula or d/1500 I have seen includes accounting for the magnification factor of the print from the original image (negative or sensor) size, which makes sensor size the critical factor. But that still assumes a "standard" eyesight and viewing distance a la "Kodak (1972)". –  Michael Clark Feb 5 '13 at 17:05
    
Circle me confused. Is the Zeiss formula for print size or sensor size? What if you have a 100% crop of an image? What is the acceptable CoC for viewing on screen? –  Rado Jun 7 at 14:14

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