IR radiation & Projectors

[P3D Dr. George A. Themelis <DrT-3d@xxxxxxxxxxxxxxxxxxxxxxxxxxx>]

Elliott mentioned that he is trying to get IR radiation specs from
GE for their halogen bulbs.  I don't think you'll get much out of
"official" specs Elliott.  What you need to do is get an estimate
of the IR radiation in your own projection system.  This can be done
by measuring the temperature seen by the slide, using one of the
following methods:

1. (most elaborate) Use a real film chip with thermocouples attached!
2. Use a temperature probe with black tape attached (certain voltmeters
   from Radio Shack come with temperature probes.
3. Use a household thermometer with black tape attached to the probe.

Note:  I insist on the black tape because black will absorb the radiation
and make your temperature measurements high, indicating the worse-case
scenario.  If you don't have any thermometers then:

4. Stick the black side off an RBT mount in front of the projector
   (don't even need to put it in the film gate).  If it melts, you have
   a problem.
5. If you are like John Ohrt who does not have any stereo mounts, then
   stick a piece of black electrical tape.  If it smokes/melts, then
   you have a problem.

These ideas are valid for any projection, not just the Stereomatic 500.
I was talking to someone today who told me that the VM projector has
(one of?) the condenser lenses made out of Heat Absorption material to
avoid sticking extra filters. I don't know if this is correct or not.

Another idea for the VM projector, since it uses mirrors to direct the
light from one bulb to two paths, is to replace the common front 
surface mirrors with "cold mirrors" (i.e. mirrors which absorb IR
radiation and reflect light that will not heat damage the slides).
These are available from Edmund.  Only problem:  Mirrors will get hot 
and that's where you need a good fan.

-- George Themelis


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