Re: filmscanners: Glass slide mounts

["William Nowlin" <williamnowlin@hotmail.com>]

Roger is quite correct.  Interference is happening all the time, even with
anti-newton-ring (ANR) glass.  Low humidity is another possible answer to your
problem.  The lower the humidity, the less problems you will experience with
Newton's Rings.  Even if you are also using ANR glass.  I have a room
dehumidifier in my darkroom and in my digital lab area.  I prefer not to use ANR
glass because I can sometimes see the pattern etched into the surface of the ANR
glass on my enlargements, scans, and contact prints.  The amount that I notice
it seems to depend on the type of image -- it's worse in areas of almost even
tonality such as clear, blue sky.  Sometimes I can't get rid of the rings
without using ANR glass, though.  I wouldn't recommend using ANR sprays or
powders.  (I'm paranoid about putting anything like that on my film.)  If you do
choose to go that route, use it very sparingly.  Less sometimes works better
than more.  Tetenal makes an ANR spray that I have tried and used successfully.

--Bill Nowlin

----- Original Message -----
From: <RogerMillerPhoto@aol.com>
To: <filmscanners@halftone.co.uk>
Sent: Friday, October 19, 2001 10:49 AM
Subject: Re: filmscanners: Glass slide mounts


It's "interference," not difraction.  The surface of any transparent ojbect
reflects at least some of the light and that light then adds to or subtracts
from the wave front traveling towards it.  Depending on the distance (as
measured in wavelength of light) between the two surfaces, the light at a given
point becomes brighter or darker.  An anti-newton surface is simple a rough
surface that doesn't reflect light as uniformly as a very flat surface, so you
don't notice the dark and light rings.  But the reflections and interference is
still going on and has the result of reducing the contrast of the image ever so
slightly.  The same thing happens in multi-element camera lenses where
reflections from each glass surface unavoidably reduce the contrast of the lens.
If you don't want to mess with glass anti-newton slide mounts, you might
consider upgrading your Nikon to a Polaroid.  (On that issue, I agree with Art
and his comment that Nikons have more of a focus problem due to!
 their weak light source and there
fore require corrective measures with curved film, such as using glass mounts.)