Re: filmscanners: Anti-Newton Rings powder

[Winsor Crosby <wincros@earthlink.net>]

>My understanding of "Newton Rings" is that they came from the same source as
>the rainbow on an oil-slick or a thin prism put on a reflector.  Namely you
>are getting 1/2 wave interference patterns from the light reflected at each
>"boundary layer" - a "boundary layer" is where the optical density, (or
>transmissivity etc ie the "C" of nu = C/lambda aka Freq = C/Wavelength),
>changes.  At all such boundary layers,  light gets reflected in proportion
>to how steep the gradient is (this is why lenses are coated to improve
>contrast - the coatings reduce the gradient).
>
>So the way to reduce Newton rings is to insure more than 1-2 wavelenths of
>separation between these reflective regions.  Putting some translucent dust
>of sufficient diameter, between the surfaces in effect acts as a separator.
>But such dust would also act as a diffuser, reducing contrast and acuity

I know people used to use it for projected slides.  I was told that 
is was composed of microscopic glass beads.  I would be concerned 
about picking them up in a scan.
-- 
Winsor Crosby
Long Beach, California