Stopping projector heat build up

[P3D <Alan.Hancock@xxxxxx>]

Bob Aldridge
Stereoscopic Society Projectionist wrote:-
>> Personally, I think it's unrealistic to expect your mount to protect
>> your emulsion from projection. You have to use a properly designed and
>> maintained projection machine, and handle the slides carefully.

>> Some slides entered for the Third Dimension Society Annual Exhibition
>> last year were slightly cooked by a Dual Hawk projector. Colin Clay
>> sorted out that problem - I'm not sure what he did to fix the projector,
>> but the machine that I use in London runs very cool. I've projected a
>> slide for SEVERAL HOURS without ANY detectable ill effects! Not even
>> perceptable bleaching...

    During my search for replacement Heat Absorbing Glass (HAG) at
    reasonable cost I had the pleasure of meeting Colin Clay at a
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Date: Wed, 4 Dec 1996 18:13:36 -0600
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    Stereoscopic Society Meeting. Although I have not yet managed to
    overheat a slide in a projector I do wish to aviod it, and we discussed
    various methods of ensuring that slides do not get overheated during
    projection. Colin was very helpfull on the subject, and subsequently
    wrote me a letter and sent copies of an informative article he published
    a while back concerning measurements that he had made with various
    projector cooling fan configurations and designs, also how to achieve
    the best level of cooling from a projector fan arrangement. I will
    contact Colin Clay and ask him if his article on projector cooling can
    be made available to all - I would be pleased to transcribe it into a
    Web site document (with appropriate acknowlegments) for all to see.

    Having recently received the Edmund Scientific Optics & Intstruments
    catalog the following HAG items are listed that I feel could be used in
    a TDC 3D projector with some adaption of the original carrier:-

    Commercial Grade
    StockNo.   Price   Diam.    Thickness
    A31,500   $16.15   63mm.    6.4mm.
    A42,783   $16.85   76mm.    6.4mm.

    Experimental Grade
    A42,784   $12.05   55mm.    4.0mm.

    Above have approx 88% absorption from 975 to 1230nm. (Infra Red band)

    'Hot Mirror'
     A43,452  $46.55   50x50mm. 3.0mm.

    The original HAG size for the TDC seems to be 59mm. diameter but the
    carrier recess will accept a 60mm. size which is an available size for
    scientific quality HAG filters. Unfortunately the cost of HAG filters of
    scientific quality in Europe is either in the region of $100 each or the
    companies able to supply are not interested in small numbers of items.
    It should be easy to add some extra clips to the TDC carrier, or
    make/improvise an adapter ring (lens adapter ring?) to use the above
    reasonably priced HAG as replacements.

    Another idea that I had was to work out if it is posible to use a 'hot
    mirror' to help stop heat build up in projectors, and I believe some
    modern projectors use this method. 'Hot mirrors' reflect infrared
    radiation (heat) while allowing visible light to pass through and
    usually have a similar percentage transmission of visible light at
    90deg. incident angle to HAG.  When using high power illumination forced
    air cooling is also recommended for 'hot mirrors' so an efficient fan to
    disperse the heat is still needed.

    Any advice or details of experiences in the use of 'hot mirrors' for
    projector cooling are welcomed.


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