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Re: [OM] More on DOF and focal length (by Ctein)

Subject: Re: [OM] More on DOF and focal length (by Ctein)
From: Ken Norton <ken@xxxxxxxxxxx>
Date: Mon, 29 Jun 2009 19:23:37 -0500
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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