Microfiche scanning - test-drb@ccmp.vtda.org

22 Apr 2005

...
 From: "Paul Koning" <pkoning at
equallogic.com>

 >>>> "John" == John Foust
<jfoust at threedee.com> writes: 
 John> At 07:21 PM 4/21/2005, you wrote:
 > You could just remove the fiche viewer
screen.  You don't need the
> screen to form the image, you only need the (virtual) image from
> the viewer's lens system to be focussed in the same plane as the
> scanner's optics.  Actually, since the image is usually focussed
> on the back surface of the viewer screen, you'd want to remove it
> anyway. 
 John> Pointing the scanner at the plane in space that happens to be
 John> the viewing plane of the fiche viewer isn't going to result in
 John> an image.  The scanner wants to see reflected light.  Focusing
 John> the fiche projection at the scanner's sensor is a different
 John> sort of problem that would involve changing the scanner's
 John> optics, no?

No.  An image is an image.  There's nothing magical about "reflected
light", it's the same as any other light.

The one issue you might run into is light loss due to mismatched
apertures. 
Hi Paul
 That is what he is talking about. The scanner would
most likely have severe vignetting. As in a telescope,
you want two things to happen where the eye is. One
is that you want the image to focus at the back of the eye.
The other is that you want the image of the aperture
to focus at the iris of the eye. In this case you'd want
the image of the source to focus near the scanners
sensor to gather the most light. This most likely doesn't
even come to a focus as is typical in projection systems.
Dwight

...

	paul