Re: filmscanners: Glass slide mounts

[Arthur Entlich <artistic@ampsc.com>]

Neil Cotty wrote:


> 
> One side effect though, maybe someone can tell me why this is happening.
> With a few slides, say 10%, I am getting this erm, multi-coloured circles
> and unusual shapes appearing on the slide. I guess it is the film itself
> perhaps slightly curved, and light playing tricks - or could it be some left
> over residue from development? It does look like a liquid! Odd, but even so,
> if it happens I just use a std slide mount instead as it does show up in the
> scan. Ideas?


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 is a big problem with glass slide mounts.  The "answer" is buying 
anti-Netwon-ring glass mounts, which have a microscopic etched surface 
to reduce the contact points.

  I find your observations about focus very interesting since I have 
been given a lot of cr*p about my postings about this problem with Nikon 
film scanners.  I was told it "didn't exist" and that I was trying to 
hurt Nikon or carry on a vendetta.

Nikon scanners use a low brightness LED illumination system which causes 
problems with depth of field, since the lens had to be quite wide to 
allow the light to pass through.  It seems to me you have empirically 
proven both the existence of the problem and one solution.

One other issue with glass mounts... they add 4 more surfaces which have 
to be kept clean of dust and dirt.  Of course, dICE is available on 
Nikon scanners to help reverse this problem.

> 
> Lastly, the Quickpoint slides seem to have a matt side, the viewing side. I
> didn't like the look of that interferring with the scans so mounted them
> reversed. Any issues with that? Having never used glass slide before - is
> that there for projection?
> 


Aha!  That matt surface is likely the anti-newton coating or surface. 
That is the side you need to have in contact with the glossy surface of 
the film to prevent the undesired colors.


Art


> Cheers,
> Neil
> 
> .
> 
>