Re: Digicam

[Kennedy McEwen <rkm@xxxxxxxxxxxxxxxxxxxx>]

In article <NEBBKHCFDGIGIJEHDJFCOEMNDJAA.pderocco@ix.netcom.com>, Paul 
D. DeRocco <pderocco@ix.netcom.com> writes
>This is interesting info. Are these rolloffs caused by the random variations
>in the grain size? Or is it related to diffusion in the emulsion?
>
Its not so much variation of grain as the finite size of the grain that 
causes this, but diffusion (caused by imperfect photon absorption) also 
plays its part.  This results in the MTF being a function of the 
emulsion thickness, which is why colour films have much poorer 
resolution than monochrome film and why the MTF is always worse for the 
red layer (bottom emulsion) than the blue (top emulsion).

And, of course, when you start working at fast apertures with thick 
emulsions the limited depth of focus means that there is no requirement 
for the lens to even approach diffraction limited resolution.

All in all, you have to work damned hard to justify sampling at more 
than 4kppi, but there is no justification for sampling at 40kppi.
-- 
Kennedy
Yes, Socrates himself is particularly missed;
A lovely little thinker, but a bugger when he's pissed.
Python Philosophers
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