The CoC is a linear measure (diameter of the circle). Therefore I think
the correct answer is a linear relationship. For a 4/3 sensor a factor
of two and not four. You can see that at work in the following
calculator (which does DoF as well as other things lens related). It
recommends 0.03mm for 35mm size and 0.019 for Canon and Nikon small
sensor cameras. That works out to be pretty much in between a 1.5 and
1.6 divisor for the crop factors of Nikon and Canon... a linear
relationship. <http://www.tawbaware.com/maxlyons/calc.htm>
Chuck Norcutt
Ken Norton wrote:
> 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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