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RE: filmscanners: LED Illumination for Film Scanners




-----Original Message-----
From: owner-filmscanners@halftone.co.uk
[mailto:owner-filmscanners@halftone.co.uk]On Behalf Of Austin Franklin
Sent: Wednesday, June 20, 2001 9:00 PM
To: filmscanners@halftone.co.uk
Subject: RE: filmscanners: LED Illumination for Film Scanners


> LEDs have been around for a very long time, and they are reasonably
> inexpensive, as well as very easy to control.  I am sure that if this was
> such a great idea, and the implementation worked near as well as you
> believe, it would have been done some 15-20 years ago as a commercial
> venture, but, alas, it wasn't.


An LED light source for enlargers was not done 15-20 years ago because it
was not possible. Blue LED's did not exist as anything other than laboratory
curiosities until within the last 5 years. High volume commercial production
of blue LED's has come about within the last 3 years, and high-brightness
versions have only been available for a about a year. Here's some history:

http://www.sciam.com/2000/0800issue/0800profile.html

http://ledmuseum.home.att.net/1990.htm

LED's are available from many manufacturers with many forms of diffusion and
light distribution patterns. With the right combination of molded LED
lenses, diffusion materials, and possibly optics a very good enlarger source
could be constructed. With the current decline of chemical imaging such a
source would possibly not be commercially viable, but it is technically
feasible. As far as the uneven character of the source shown at
http://www.trailing-edge.com/www/led.html , it's no worse than the three
lamp sources found in RGB color heads in some additive enlargers. The
individual bulbs used there are spaced a couple of inches apart and yet
their light is mixed to provide an even, color controlled source.

The light source shown on the above site is obviously a prototype; it uses
what appear to be narrow beam clear lensed LED's. If diffuse lensed wide
angle LED's were used along with a secondary diffuser or lens, you'd see
much more even illumination. There's no reason that desire and a little
innovative engineering could not produce an acceptable source. Economics
might be a tougher nut to crack though.

Cliff Ober




 




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