My quick study of this matter a few years ago had

me turn my attention to the purchase of an OM-10.

A more thorough study this pass confirms the

equation you use to be THE one to use. Print

size divided by negative size is specified

to be the method for deriving M&m.

Although a + 1 in each term appears to compensate

for aperture changes and the equation is described

as being accurate, I've not encountered any claims

of it being exact. So I wonder if the equation is

the last word?

Without the + 1s results will equal those of the

equation Nt = Ot x Ne^2/Oe^2; where the terms

are Old, New, time, and edge.

For more information on this subject and derivation

of other exposure related variables search Google

for, exposure enlargement calculations . Dan