Re: filmscanners: Glass slide mounts

[RogerMillerPhoto@aol.com]

In a message dated Fri, 19 Oct 2001  4:22:32 AM Eastern Daylight Time, Arthur 
Entlich <artistic@ampsc.com> writes:
> The effect you are seeing is called Newton Rings, and it happens 
> whenever two glossy surfaces come in contact.  I believe the colors are 
> determined by how many molecules of air are between the surfaces, a type 
> of defraction.
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.)