Depth of field calculations

[P3D Neil Harrington <nharrington@xxxxxxxxxxxxx>]

Paul S. Boyer writes:

>DEPTH of FIELD Calculations
>
>The first step is to find the hyperfocal distance for your setup.  If
>one focuses at the
>hyperfocal distance = H, everything should be sharp from 1/2 H all
>the way out to infinity.
>
>I would use a circle of confusion of 0.03 mm.  
[ . . . ]

That's pretty close to the size that seems to be usually assumed for depth
of field purposes, at least by Japanese camera manufacturers.  Several years
ago, out of curiosity, I "reverse calculated" the circle of confusion from
Minolta's published d.o.f. tables, and my recollection is that I got a value
of .033 mm or thereabouts.

So I assume from that that the Japanese generally take 1/30 mm as a
tolerable circle of confusion.  German manufacturers seem to be somewhat
more generous, as you can see by comparing the d.o.f. scale on, say, a Leica
50mm lens with that on a Minolta 50mm lens.  The Leica scale indicates
substantially greater d.o.f. at similar settings.

All this means, of course, is that different assumptions are being made
about what is tolerable, and, presumably, what the degree of final
magnification will be.

Cox writes (in PHOTOGRAPHIC OPTICS) that the largest circle the eye will
perceive as a point, at the closest comfortable viewing distance of ten
inches, is about .01 inch.  That's about .25 mm, so if one assumes a final
magnification of 4X (typical drugstore print from a 35mm negative), an
acceptable circle of confusion would be about .063 mm at the negative,
ignoring losses.  Assuming instead a magnification of 6X (close to that of a
Realist-format viewer), the circle of confusion would be no larger than .042
mm.  Assuming a magnification of 12X (e.g., an 11 x 14 print), it would be
about .021 mm, again ignoring losses.  And so on.



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