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Re: filmscanners: Stains and Grains (was Yellow Stain)
Lynn Allen wrote:
> Thanks, Art. So as I see it from your diagram, there *could* be a light
> fall-off outside the areas seen most clearly by the lens. I don't know how
> that would be measured, but with the Yellow Stain phenomenon, it's clearly
> in Kelvins, since it goes to yellow from what should properly be blue, but
> does not approach red in anything I've seen (although if "red" were there to
> begin with, it would be darkened).
I guess I should explain that the little drawing I did is very stripped
down, and unlikely to show what any scanner really looks like. Due to
the need to increase depth of field, most scanners actually use a folded
optical path which requires some mirrors, thus increasing the length of
the path and the potential DOF, but also complicating the number of
components and places for problems to develop. Without seeing the
insides, I would be hard pressed to guess at the cause of the lowered
light source/ and or color temperature at the edges of the scans.
The need for the folded light path explains, in part, why film scanners
are as large as they are.