Calibrating color heads for B&W printing.

Discussion in 'Enlarging' started by Eric_Fr, Apr 27, 2004.

  1. Eric_Fr

    Eric_Fr Member

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    Hello,

    I'm new to your forum; I just discover it few weeks ago and find it very
    interesting for a newbie in Darkroom process.

    I have seen in a previous topic "Determining contrast grade in the Darkroom" that some people consider that the exposure time stay the same as you change contrast grade. I'm surprise by this affirmation and I would like
    to know if some of you have realize a calibration of their system like
    define by Paul Butzi in is web site.

    http://www.butzi.net/articles/vcce.htm

    Excuse me for my poor english.

    Best regards,

    Eric.
     
  2. clogz

    clogz Subscriber

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    Hello Eric,
    Welcome to APUG
    Butzi's method is very precise. If you are a newbie to darkroom work it may be better to use dual filtration (Y+M). The exposure time you find with a test strip remains the same for grades 1-3 VC paper.Grades 4 and 5 need double length of exposure.
    Hope this helps
    Hans
     
  3. Ole

    Ole Moderator Staff Member Moderator

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    Poor English is not a problem on this site, Eric!

    I adjust the illumination to give the same exposure at all grades: My Opemus 6 colour head has four filters: C, M, Y, and N. The N is a neutral filter giving two stops fine-tunability.

    It just so happens (intentionally?) that my EM10 exposure meter will give the lightest near-white a reading of 85 on all grades of Ilford MG IV RC at 10 seconds exposure. So I twiddle the "N" until the EM-10 shows 85 for the densest part of the negative that I want almost, but not quite, white.'

    The meter setting at the thinnest part of the negative (my shadows) determines the grade needed to fit everything onto the paper without burning/dodging. I have a diagram made up that I consult.

    So I start without filter, adjust "N" and aperture to give 85 in highlights. Then I measure shadow, determine wanted grade, set "Y" or "M", then change aperture and "N" until highlights are 85 again. Expose 10 seconds, develop and fix.

    Then I'll probably decide that the contrast is too flat, change the settings again, and start burnig and dodging. But I stick to that 10 seconds base exposure.
     
  4. Thilo Schmid

    Thilo Schmid Member

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    Eric,
    welcome to APUG.

    It is sometimes useful to know some "basics" in order to understand why certain things are the way they are.

    VC-Paper is built of two emulsion layers with different spectral sensitivity and different gamma (grade). As long as you stay with grades 1-3, both layers are exposed in a way that the overall speed stays the same. At grades 00/0 and grades 4/5, basically only one layer, with each about half the speed, is exposed.