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Infra red filter

Discussion in 'Colour or Not' started by John_K, Sep 15, 2010.

  1. John_K

    John_K Well-Known Member

    I have just uncovered my Cokin IR (opaque red) filter. Can anyone remind me how many stops should I allow when using this. I seem to remember something like 8 or 10. It will be on Ilford SFX Film nominally rated at 200ISO.
     
  2. taxor

    taxor Well-Known Member

    Hi John, is that the Ilford dedicated SFX filter? If so, I got very good results with +4 stops. Mind, I suppose it depends how you dev the film. I used D76 for 10.5 mins 1+1. Good luck.
     
  3. John_K

    John_K Well-Known Member

    I bought the film at the same time as the filter as a special offer and they came bundled together. The filter mount is embossed Cokin but the filter itself is a gelatine sheet.

    I used it a while back and have forgotten how many 'stops' to allow. I seem to remember 6 or 8 but I may be mistaken. I also remember developing it 1-1 in ID11 for the time recommended by Ilford. That worked out fine for me.
     
  4. taxor

    taxor Well-Known Member

    Yep, you're using the SFX filter. Mine also came bundled with a roll of SFX. The SFX tech sheet gives a filter factor of 16(4 stops). I got my dev. times wrong. I actually used Ilford's recommended time for D76 of 14.5 mins 1+1.
     
  5. John_K

    John_K Well-Known Member


    Filter factor of 16? Well in old money that should be 8 stops! An ordinary yellow filter with a factor rating of 2 was one stop. An orange with a factor of 4 was 2 stops. A red (normal not IR) was 6 = three stops so 16 should be 8 stops. Or is there something I have not taken into account?
     
  6. taxor

    taxor Well-Known Member

    Hiya John. Filter factors double up for every 1 stop increase.
    Filter factor 2 = 1 stop
    4 = 2 stops
    8 = 3 stops
    16 = 4 stops
     
  7. John_K

    John_K Well-Known Member

    Thanks for that I thought there must be something. I will bracket anyway.
     
  8. Mojo_66

    Mojo_66 Well-Known Member

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