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  1. #11

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    Sorry ... I noticed a typo ... my cold light system is accommodated to green and blue tricolor. Didn't
    mean to say red. (I had just responded to an additive COLOR printing question on a completely different forum, where red is also relevant).

  2. #12
    ic-racer's Avatar
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    Quote Originally Posted by David Lyga View Post
    The other day I tried exposing VC paper using a circular blue camera filter (the one for exposing color film under tungsten), instead of the standard VC filter, and found out that using the highest grade magenta filter (intended for VC printing) gave slightly more contrast. I thought that 'blue' was the color needed for the highest contrast. Comments? - David Lyga
    The 'blue' filter you used passes too much yellow to achieve the maximum contrast available from the paper. What is wrong with using the #5 VC filter?

  3. #13

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    IC- the blue filter passes too much green, not yellow.

  4. #14
    David Lyga's Avatar
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    cliveh: the magenta is best for highest contrast because, as others have re-iterated, it stops most of the green. The green (and yellow) LOWERS contrast. The lighter blues let it through. - David Lyga

  5. #15
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    It's worth a look at Ilford's data sheet for variable contrast papers. They state that all of the emulsions are sensitive to blue and the varying contrast layers have varying amounts of green sensitising dye added.

    When the paper is exposed to blue light, all parts of the emulsion react and contribute equally to the final image. This image is of high contrast because of the additive effect produced by three emulsions with the same speed and contrast.
    When the paper is exposed to green light, only the parts of the emulsion with the larger amounts of green sensitising dye react initially. This is because the three emulsions have very different sensitivities to green light. This image is of low contrast because of the additive effect produced by three emulsions with different speeds to green light but with the same inherent contrast.
    http://www.ilfordphoto.com/Webfiles/...8932591755.pdf

    So a bit more complex than one emulsion sensitive to blue and another sensitive to green.


    Steve.
    Last edited by Steve Smith; 12-21-2012 at 10:01 AM. Click to view previous post history.
    "People who say things won't work are a dime a dozen. People who figure out how to make things work are worth a fortune" - Dave Rat.

  6. #16
    RalphLambrecht's Avatar
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    drew is spot on, butdon't forget one other variable, and that is light intensity. regardless of color. more light willgive more xposure. even a narrow-band red diode will expose the paper over time and make a poor safelightgiven enough time.
    Regards

    Ralph W. Lambrecht
    www.darkroomagic.comrorrlambrec@ymail.com[/URL]
    www.waybeyondmonochrome.com

  7. #17
    ic-racer's Avatar
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    Quote Originally Posted by Michael R 1974 View Post
    IC- the blue filter passes too much green, not yellow.
    Of course, thank you.

    Anyway, getting back to the topic on hand I would predict a speed advantage using the Ilford #5 filter. I'm surprised I did not test for speed when comparing the #5 to all my magenta dichroic filters. But if you just look at the #5 you see it is not just a magenta filter. I suspect the #5 has some some unique spectral parameters, but Ilford does not give the specs. I have subsequently given away my Ilford filters so can't test it now.
    Last edited by ic-racer; 12-21-2012 at 11:33 AM. Click to view previous post history.

  8. #18

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    Even among papers offered by Harman the different VC papers have different nuances, which one
    just has to learn by experience. But if one is going to jump into the pool in the first place, it's easiest
    to teach simple Blue versus Green tricolor, or basic Magenta versus Yellow variable filtration. Once
    these basics are understood, then the more complex interactions of the actual paper engineering can
    be fine-tuned, like adjusting the water temperature after you dive in. It's a lot easier to demonstate
    on test strips than it is to explain. No need to make a religion out of any single method.

  9. #19

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    Quote Originally Posted by ic-racer View Post
    Of course, thank you.

    Anyway, getting back to the topic on hand I would predict a speed advantage using the Ilford #5 filter. I'm surprised I did not test for speed when comparing the #5 to all my magenta dichroic filters. But if you just look at the #5 you see it is not just a magenta filter. I suspect the #5 has some some unique spectral parameters, but Ilford does not give the specs. I have subsequently given away my Ilford filters so can't test it now.
    I'd be glad to send you a spare set. You make a very interesting point here. I've wondered why when examining the current Ilford MG filters, the #3 seems to visually appear the most Magenta in colour, and the higher numbers look more orange again.

  10. #20

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    Variable contrast paper is essentially two emulsions coated on one paper base. The low contrast emulsion is green sensitive and the high contrast emulsion is blue sensitive (positive filtration). Magenta and yellow are negative filtration. With a VCL aristo head the two tubes are blue and green, green at 100% out put and blue a various percentage of out put controlled by a rheostat to create various contrast grades.

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