Re: Cooling Stereo Projectors

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

Thanks to Peter Pehnallow for reposting a very interesting article by
world renown projection expert, Colin Clay in UK.  Peter, somehow your
message appeared at a 48K (very long!) posting with lots of weird
characters (is this the FIGS.ZIP attached file?)...

>From this posting I picked up three interesting items:

>      9.  Only small amounts of air should be allowed to flow past 
>quartz-halogen lamps as they arc designed to operate at high temperatures 
>in order to maintain the tungsten-halogen operating cycle.

In practical terms, does that mean that when we switch from the common
tungsten to halogen bulbs we will need to change air circulation to
reduce the cooling of the halogen bulbs?  And doesn't that increase
the potential of cracking the bulb holders, especially the bakelite
ones in the TDC 116?

>      HEAT FILTERS
>    3. The filters should be protected from moisture due to their rather 
>unstable surfaces.
>       Condensation can be a problem if the projector becomes cold in 
>transit and is then taken in to a warm, humid environment.
>    4. The filter surfaces should be examined at periodic intervals to 
>see if they have deteriorated. It may be possible to restore the surfaces 
>using glass polishing compounds such as those used for producing 
>telescope mirrors. Alternatively it could be worth trying paint cutting 
>compounds made for cleaning car paintwork, and finishing off with metal 
>polish.

Good advice and good solution, especially for TDC 716 owners using 750W
bulbs.  By now I have seen a few cases of etched heat filters, result,
I believe of humidity + high temperature.  TDC 716 owners w/750W bulbs
should examine the filter surfaces per Colin's suggestion.

>    LOCATION OF POLARISING FILTERS
>    As mentioned in previous Clinics, I have found it to be of 
>considerable advantage to position the polarising filters behind the 
>slide. This considerably reduces the heat transmitted to the slide and 
>hence offers significantly better protection to our valuable and often 
>irreplaceable slides.

This is an interesting point... From previous discussions the conclusion
was in the air that the best position (I guess in terms of polarization)
is after the lenses... But cutting heat from the slide is an advantage
that was not considered...

>    Particular care should be taken to obtain a good flow of cooling air 
>over the filters, as they will obviously become quite warm in operation. 
>Their polarising properties are greatly reduced if they become 
>excessively hot for protracted periods. The selected location in the 
>projector should ensure that the beam of light has the greatest possible 
>diameter, so the preferred location is close to the bi-convex condensers. 
>This distributes the heat over the biggest possible area and avoids the 
>concentration of heat...

Thanks Peter and Colin!


------------------------------