How to make (where to buy) a swinging center filter for HID source?

Discussion in 'Alternative Processes' started by guruguhan, May 29, 2006.

  1. guruguhan

    guruguhan Member

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    Hello,

    I'm looking for pictures/instructions or where to buy a kit to add a swinging center filter to an HID source (as described in Sandy's light sources article on UnblinkingEye).

    I have no idea what these look like/how they connect/anything.

    Thanks a lot

    Gu
     
  2. donbga

    donbga Member

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    AFAIK, you will need to make your own.
     
  3. sanking

    sanking Member

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    Gu,

    You will have to make your own, and calibrating it is not easy.

    In principle, the filter is just a round disk (I used phenolic plastic) about 5-6" in diameter which you place several inches under the center of the bulb of the HID lamp. It is held in place by a very small diameter rod or bar that you attach to an adjacent wall. Depending on design, you may also place small holes in the disk to even out the light source.

    In essence, the filter eliminate the light that comes from directly above so that the print is exposed with reflected light. The theory works, but getting it just right takes a long time so in practice it is best to just increase the distance of the bulb from the printing frame and even the light out this way. Exposure times will be about the same both ways.

    Sandy
     
  4. mark

    mark Member

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    How big a print are you making?

    You said you were using a 1000 watt bulb so why would you need a center filter? You can get very good and even illumination from a 1000 watt MH bulb over an area that measures roughly twenty four inches square, with light fall off being very moderate up to 36 inches square. I print 8x10 POP with no issues what so ever and I never have it centered under the bulb. Might be easier to find a good reflector on the used hydroponics market, than to build a center filter and try to calibrate it.
     
  5. guruguhan

    guruguhan Member

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    Thanks a lot for the info everyone.

    Mark: size of print is 16x20 (up to), but the initial light-to-print distance I was hoping on was 20-25", prompting the filter question. I'm probably going to set the light up in another area so I can avoid the filter and increase the distance.

    Gu