Re: scanner glass replacement

["Ernst Dinkla" <E.Dinkla@xxxxxxxxx>]

----- Original Message -----
From: "Arthur Entlich" <artistic-1@shaw.ca>
To: <scan@leben.com>
Sent: Sunday, April 28, 2002 3:13 AM
Subject: Re: scanner glass replacement


> Where are there good sources for such glass?  Do most glass
suppliers
> carry it, or is it only available from certain facilities?  Is
it made
> to order for scanner companies, or is it a generic glass they
simply
> order? About how much is it a square foot, or is it only sold
in set
> sizes?  Does it vary in thickness?  Is there a standard
thickness used
> for most letter and legal sized scanners?

I did some searches on the web as I intend to make a DIY glass
carrier for the Nikon 8000 based on a non glass carrier (ordered
it 2 weeks ago but it takes time).

There's an English version on this website of a German optical
glass distributor;

http://www.optische-komponenten.de/intl/index.html

I think for most flatbed scanners the optical glass quality falls
in the category 'selected white float glass'. Above that is the
same glass but with an extra polishing on both sides. With float
glass the side that was in touch with the molten tin is the most
plane side, the flame polished upside can show some
irregularities like stria. The usual faults are bubbles in the
glass and tiny parts of tin that stick to the underside, the last
show up as tiny mirrors. For the sizes of  flatbed scanners it
should be possible to find good pieces at a local glass shop I
guess. Flatness and an even thickness can hardly be a problem.
Ask them to cut more sheets carefully, the price can't be a
problem. Handling afterwards and polishing the edges is more of a
problem. Then select the best on close inspection.

What surprised me is that float glass in larger sizes doesn't
have to be plane entirely. One would expect that the tinbed
method always creates a planeness equal to the worlds radius.
Changes in the weigth of the glass within the machines production
size can create differences though. Not important for scanner
glass.

Ernst







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