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Larry,
So sorry to be a while getting back. Here is a version of the formula which will calculate depth of field by measuring the depth of focus.
Aperture = focus spread divided by 2 times acceptable circle of confusion.
For a normal viewing idstance for an 11 x 14 print the acceptable circle of confusion for a 4 x 5 neg is 0.066 and for an 8 x 10 neg it is 0.133
There is yet another theory and equation which compares focus spread and DIFFRACTION. Viewing distance, magnification and negative size become irrelevant and an optimal stop for the given focus spread is given. That equation or formula is:
Optimal aperture = square root (375 times focus spread)
These formulae work fine in a Palm Pilot spread sheet and, from my experiences so far, seem to be on the money.
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