Re: To David Soderman: A Little Test

[Kennedy McEwen <rkm@xxxxxxxxxxxxxxxxxxxx>]

In article <000401c1e25d$55712980$0100a8c0@KAIROS>, Ernst Dinkla 
<E.Dinkla@chello.nl> writes
>
>Kennedy, what kind of glass could I use for a film carrier ?
>Some companies that sell optical glass sell quality picked float
>glass, nothing special in fact. Up to 1.1 mm the thickness
>variation is within 0.05 mm. On a piece of 300 x 115 mm it will
>be less than that. The Nikon carrier + scanner would allow  up to
>1.5 mm thick glass maybe 2 mm but nothing above that.
>
I would be more concerned with the surface quality (digs and scratches) 
and the colour purity than the thickness variation itself.

The main issue that you will have from the glass thickness is a focus 
shift (which the autofocus should accommodate) due to the optical path 
being around 0.67x the thickness of the glass on the CCD side of the 
slide.  Secondary issues like spherical aberration and defocus due to 
the thickness variation should be negligible.

Most float glass should be adequate, but if you can get selected glass 
for a sensible price step then go for it.  Can you get hold of some 
etched anti-newton ring glass?
-- 
Kennedy
Yes, Socrates himself is particularly missed;
A lovely little thinker, but a bugger when he's pissed.
Python Philosophers
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