Color Contrast Filters

This is a discussion on Color Contrast Filters within the Darkroom forums, part of the FILM PHOTOGRAPHY FORUM category; Enrolled in "studio B/W photography II" at school and after a summer focusing on digital processing, its been fun to go back to film. While ...


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  1. #1
    Senior Member
    Join Date
    Jan 2008
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    256
    Enrolled in "studio B/W photography II" at school and after a summer focusing on digital processing, its been fun to go back to film. While doing so I learned to use the "filter" function on Canon DPP and Photoshop and enjoyed the results. When I got back to school I noticed that all the contrast filters were magenta (rather than green, yellow, orange). Is this filter function simulating a contrast filter used in the darkroom, or a filter attached to a camera lens? When I asked my instructor if there were any other colors, he said "nope, just shades of magenta." Or is it simply a "digital thing?" If not does anyone know where to find these filters?

    Thanks,
    "rookie-ish" film printer, Monkey.
    Canon Rebel 400D/XTi, EF-S18-55mm, EF 70-300mm IS USM, EF-S 60mm f/2.8 Macro, EF-S 10-22mm, Speedlight 430EX II


  • #2

    Join Date
    Nov 2009
    Location
    Lawrence, KS
    Posts
    186
    I am not sure if I'm understanding your question right, but here's what I know...

    The magenta and yellow filters used in the darkroom are to control the amount of green and blue light the photo paper gets. Variable contrast BW papers have several layers of emulsions that react differently to variations in the green and blue light. When a strong magenta filter is used green light is blocked, and blue light gets through resulting in high contrast. When a strong yellow filter is used blue light is blocked and green gets through resulting in low contrast. Varying the amount of green and blue allows for a range of contrast. But this effect is manufactured into the paper. Blue and green light are what the emulsions are sensitive to, but if the emulsions were sensitive to red light it could have just as well been that. Which particular color is used is not important other than that's what the chemicals in the emulsions happen to be sensitive to. If you put these filters on a camera lens it would not give the same effect on contrast. For one the green/blue sensitivity contrast adjustment is only built into the paper, not film or digital sensors. You could load a camera with BW paper, but then you'd still have to deal with real world color which would also effect the amount of blue and green light. The filters are meant to be used with an enlarger lamp projecting through a BW neg.

    Variable contrast filters are available anywhere they sell darkroom equipment and on Ebay.

    Check out split contrast printing http://www.photogs.com/bwworld/splitfilter.html

    Putting a colored lens on a camera loaded with or set to shoot BW or using the channel mixer in Photoshop to convert to BW is subtracting or adding gray scale tone value based on the colors of visible light. A strong red filter makes cyan darker because it is blocking most of the cyan colored light so those areas expose less. It is also blocking some green and blue. More orange and yellow light are getting through, and no red light is blocked making anything red get more exposure than the rest. The channel mixer in PS, and the grayscale sliders in newer versions of LR and ACR are similar.
    "I donít use an exposure meter. My personal advice is: Spend the money you would put into such an instrument for film. Buy yards of film, miles of it. Buy all the film you can get your hands on. And then experiment with it. That is the only way to be successful in photography. Test, try, experiment, feel your way along. It is the experience, not technique, which counts in camera work first of all. If you get the feel of photography, you can take fifteen pictures while one of your opponents is trying out his exposure meter." -Alfred Eisenstaedt


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