Re: Glass for UV exposure frames?

From: Sandy King (sanking@hubcap.clemson.edu)
Date: Mon Dec 06 1999 - 20:49:59 /etc/localtime


You may be correct in the assumption that glasses which transmit a high %
of light below 350 nm will give you "the best results you are going to
get", but I would not assume that to be so without a closer understanding
of exactly what the words "best results" mean, and some actual tests to
verify results. It may be true that normal glass does not transmit as much
UV light as the B-270 type glass but it is also true that there are some
very undesirable qualities of light below 350 nm,including 1) additional
risk to human eyes, and 2) the very low contrast of light sources below 350
nm. With dichromated colloid systems in particular you get images
increasingly low in contrast with light sources in the far UV range. The
system is much more sensitive to the light in this range but the resulting
images are increasingly lower in contrast with decreasing # nm . This has
been know for a very long time. J. M. Eder did experiments with this
(sorry, don't have reference on hand) and his results agree with my own
long term observations about light wave length and image contrast with
colloid systems.

Sandy King

>Michael,
>Try contacting Glennview through Photomall.com. He sells sheets of
>multicoated optically clear glass. I don't have the specs, but knowing a
>bit about glass and such, I would say that this glass is probably B-270
>glass or equivalent which transmits 30% at 325 nm assuming no coating
>and a 8% loss due to the two air/glass interfaces. Since it is
>multicoated, there will probably be only 2% loss in the visible
>spectrum, but probably a little higher in the UV. "Normal" glass does
>not transmits as much UV as this does. It isn't real cheap, but I would
>invest in this glass. I'm sure it will give you the best results you are
>going to get. I'd be interested in seeing those spectral curves if you
>don't mind sending them to me either by email or fax. (978-657-8643)
>Thanks!
>
>Dave



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