RE: filmscanners: 6x8

[Bruce Kinch <pvx@ma.ultranet.com>]

>There should not be as we are using Newton free glass as one of the two
>pieces. Why only one is Newton free I frankly don't know but I am told that
>is all that is necessary.
>David

Newton rings are an interference cancellation from light trying to 
get through two transparent but reflective surfaces that are less 
than a wavelength apart.

Anti-Newton glass is very slightly rough or textured. The AN glass 
normally is used only on the base (top) side of the film. Most roll 
film, esp 35mm, has a shiny base, partly to reduce scratches during 
film advance I presume, but that makes it prone to the problem. Most 
sheet film has a "retouchable" surface, with enough "tooth" that a 
pencil can be used, and that alone eliminates Newton Rings. The 
emulsion side of any film is itself sufficiently rough to not need AN 
glass. Besides, if used between film and optics, AN glass would 
degrade the image.

Dust is less of a problem than it might seem (most is out of focus), 
and is worth noting that you may not need any glass on the bottom at 
all, if the film is supported by the carrier on all four sides. The 
Leica Ic enlarger was (and still is) legendary for it's image 
quality, and it used a single condenser lens directly atop 35mm film. 
They later sold a special AN glass that slipped under the condenser 
when the problem became apparent with modern films. As an aside, I've 
refurbed a couple of these for friends, and as the AN attachment is 
impossible to find used, I have used slide mount AN glass or an 
unmounted soft-focus filter as substitutes-they worked perfectly.

Old timers used to buff glass enlarger carriers with "Jeweler's 
Rouge", an ultrafine abrasive. No need to today. I've had students 
make AN glass carriers for years, using "non-glare" picture framing 
glass on top, and plain below, with a tape hinge. Amazing how much it 
improves sharpness in conventional printing. Probably do the same in 
a scanner. In fact I may make one for my 4000SS before David does:-)




-- 
Bruce C. Kinch
Associate Professor of Photography
The Art Institute of Boston at Lesley University