[filmscanners] RE: IV ED dynamic range

["Austin Franklin" <darkroom@ix.netcom.com>]

> > As far as I remember, theoretical dynamic range's
> > maximum is 4.0 which is ideal ...
>
> There is no theoretical limit to dynamic range.  It's like a Richter or
> decibel scale, open-ended in one direction.

There IS a theoretical limit to DENSITY range, which is what you mean when
talking about what you're talking about:

6000°C black body (solar photosphere temp) emits about 3.405E25
photons/sec/ster/m^2 between 400 and 750nm.

25°C black body is around 3.884E-3 photons/sec/ster/m^2.

It is possible to get brighter surfaces, but the UV content would be a
problem for the sensor, and it is possible to run the scanner colder, so
getting a lower thermal black emission, but these are probably beyond
practical limits anyway.

Assuming a light source area of approximately 1000th area of the film
surface, being totally focused onto the film area, and "black" emission
from the film surface, that results in a contrast equivalent to a dMax
of 25.

Austin



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