Does the cooling fan protect slides in projection?

[P3D Dr. George A. Themelis <fj834@xxxxxxxxxxxxxxxxxxxxx>]

I made this statement and has not been challenged yet.  It appears to me
that the cooling fan is there to protect the projector and not the slides. 
This is a result of the observation that the temperature of the slide in
the projection beam rises steadily as it absorbs radiation.  One would
expect that the cooling stream of air will cause the temperature to reach
an equilibrium point. However, my observation has been that the temperature
is still rising in the short period of time that the slide remains in the
beam's path.  The heat-absorbing filters or cold mirrors block the IR
radiation from heating the slide and these are the ones that essentially 
protect the slide.

So:  - heat absorbing system (filter, mirror) protects slides
     - cooling fan protects projector

Is this roughly correct?  If it is, those who have problems with melting
RBT mounts should check the fitlers.  If the projector feels very hot and
parts of the projector are cracking from excessive heat then the fan is in
fault.

George Themelis


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