Begin Forwarded Message:

From: Mark Fontana <fontana@cis.ohio-state.edu>¶
Subject: Re: Light Sources for Optical Reader¶
To: rhodes@foxtail.com (Robbie Rhodes)¶
Date: Sun, 7 Jan 1996 20:41:08 -0500 (EST)

You wrote...

> To get the best efficiency from the a light source some sort of
> condensing lens system is needed ...

This is something I haven't explored yet with my (admittedly crude)
scanner.  I got the light rays "parallel enough" by putting the light
source about 3.5 feet above the tracker bar.  Having the light
any closer (or more than one light source) caused light to spill
through one exposed hole over to the adjacent detectors.

The software and digital I/O side of my scanner is pretty good.
But the machine itself needs a lot of work, and I just don't have time
to mess with it right now. ... {snip}

> The rays of the light source ideally converge at the iris stop
> in the projection lens.

Never tried this, but this is essentially what I did when focusing
the lamphouse in a 35mm movie projector.  (Instead of the filament,
you see a round dark spot- the shadow of your carbons (or the xenon
bulb's electrodes).

> You could easily use an overhead projector for the light source ...

I should try this -- it might reduce the spillage I mentioned earlier.
One attempt I made to reduce the spillage was to fill the tracker
bar holes with black paint and then scrape away just enough to
trigger the detectors.  This was also an attempt to get the detectors
to all trigger at about the same threshold.

If I end up scrapping the scanner, I guess I can always use the
digital I/O boards for output and build a computer-controlled
orchestrion.  :-)

Mark