Here is an interesting site with simple explanation of CoC, I believe CoC
should be linear not surface area.
http://www.cambridgeincolour.com/tutorials/diffraction-photography.htm
C.H.Ling
----- Original Message -----
From: "Ken Norton"
> Something about the DoF calculations that has been bugging me. If we use a
> starting CoC of 0.03mm for 35mm as our start point and we use 50mm as our
> focal length, what CoC should we use for a film/sensor format that has
> exactly 1/2 the diagonal size and 25mm as the focal length?
> The common thought is 1/2 of the 35mm format which is 0.03mm. But is this
> correct? If we alter the CoF to be 1/4 of that of the 35mm format to
> base
> this on surface area, not diagonal, then the DoF calculations match.
>
> So, what I'm getting at is whether or not or CoC should be a diagonal
> distance calculation or a surface area calculation?
>
> Math is math, but again, we have to ask ourselves what the basis of our
> calculation is.
>
> AG
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