Projector Heat filters

[P3D <Alan.Hancock@xxxxxx>]

Dr. T wrote:-
>> I have seen this condition in only one TDC 716 projector that eventually
>> sold to Alan H. in England.  It appeared that something (liquid) was
>> spilled into the glass?  It was in both sides.  I wondered if it was the
>> result of humidity of something.  I tried my best to clean the filters.  I
>> removed most of it but there was more left.  I was hoping that Alan would
>> be able to either fix them or replace them.  Sorry to hear that this is
>> still a problem.  I have not seen this condition in any other TDC projector
>> that I have examined.  -- George

    Dr. T. - Thank you for your concern. The TDC 716 projector you sold me
    was a bargain and I was very pleased to be able to afford to purchase
    one at all. The condition of the filters is such that it does not stop
    the projector from being used. Being a bit of a perfectionist, as I am
    sure Dr. T. also is, I decided to investigate the possibility of direct
    replacement with modern high performance filter material.

    At the same time I was curious to find out if other people had
    experienced the problem with other TDC heat filters and heat filters in
    projectors in general.

    A theory that I have about the white fogging that has been seen on
    several TDC heat filters, is that the it is a result of a deposit
    from a vapour sticking to the hot or over heated surface of the filter.
    Over a period of time the surface contamination changes the properties
    of the glass at the surface helping it to become slightly ridged and
    pock marked. A possible source of such a vapour being an oil vapour
    generated by the cooling fan or cigarette smoke being drawn in from the
    room.

    A source of supply of the 60mm x 3mm (nominal) sized heat filters at
    economical cost is yet to be found. Edmund Scientific have some heat
    filters in their optics catalogue that might suffice with a home made
    adapter ring or filter carrier.

    I am also looking into making a kit to convert the VM 500 Stereomatic
    projector to take heat filters. The size required of filters for the VM
    500 are more readily available.


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