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Colour filters?

Discussion in 'Projectors, Screens & Video Processors' started by gnarvster, Apr 14, 2005.

  1. gnarvster

    gnarvster
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    Hi!

    What's the deal with colour filters? I suppose they are just coloured lenses for the optics right? Then, is it possible to buy colour filters and install yourself, sort of like you install colour filters on a camera lens.

    If filters improve colours as much as people say, where do i get them? :)

    Or perhaps it is not that easy.
    Sorry if this is a dumb question, I'm all new to the CRT (in projected form ) business ;) (had my share of monitor repairing in my days)
     
  2. Roland @ B4

    Roland @ B4
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    HI Gnarvster

    Colour filtering has become the next stage in tweaking CRT's to achive better saturation.

    The reason filtering is nessary is that the phosphors used in CRTs are not pure. Both the Red and Green carry too much yellow. Tending to make the reds a bit orange and the greens a bit light. (the blue is about right)
    Manufactures did not fit them as standard because any form of filter cuts down the light and that is not good on the specs ( most projectors were only showing spead sheets and presentations to the corporate market any how)

    Once we start using these projectors for cinema, colour becomes more important and light output is less of an issue so filters are OK.

    There are essentailly three ways of doing it.

    Replacing one of the elements within the lens with glass that has the correct colour (ie red or green). In practical terms these means replacing the whole lens assembly. This tends to be expensive especially with the largere lenses like the 808. There is a whole buzz going around at the moment concerning the replacement of the standard 8" lenses on 808 with the colour filtered ones designed for say Cine 7.

    Some projectors use an element "C" of the lens attached to the front of the tube itself. The void behind this is filled with a special optical fluid. It is possible to change this part of the lens with a coloured one.


    The second more basic way of colour filtering is to put, as you say, a coloured filter in the light path. Finding glass of the right colour, size & thickness is a real problem so most people have used coloured gells. the biggest issue with these is adding another surface in any optical path will induce further internal refections. but it is an excelent way of improving colour on a budget.

    The third and less common is to add a colour dye to to cooling fluid that sits in between the glass surfaces of all CRTs
    In some projectors
     
  3. gnarvster

    gnarvster
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    Thank You very much Roland for this kind and thorough explanation! My projector is an old NordMende TVP-100 which I think has only about 300lumens output, so perhaps colour filtering is a bad idea.

    (BTW Does anyone know anything about this projector?)

    I haven't received the projector yet so i don't know how the colours are, and in what condition the tubes are. I'll know in a few days. This is my first CRT projector, and I know it's not particulary good. It's going to be interesting to see what it can achieve picturewise.

    Anyway, thanks again for the info, much appreciated !
     

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