Mark writes:
===========================
I understand the basic theory but your equation is at variance (no pun with
mean, standard deviation and variance) with John Petrush's equation of:
(1/R)**2 = (1/Rl)**2 + (1/Rf)**2
============================
They are both just approximations that give a fairly reasonable estimate of
what is going on. In a real system, there also are other factors that
contribute to less resolution, eg focusing errors, vibrations, etc.
So I personally prefer the more conservative estimate given by the
equation 1/R = 1/Rl + 1/Rf but you can pick whichever you like, as they are
just estimates. the root-mean-square form, given by John is probably a
better estimate if you are looking at only the lens and film together
as a system with all else operating at perfection.
And John writes:
===========================
However, film resolution is not fixed. It too varies with lens aperture,
and inversely with lens resolution.
===========================
I've never heard that film resolution varies with lens aperture, and it
is rather counter-intuitive-- might you be able to explain why this
would be?
Cheers,
Joseph
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