Chromega Subtractive Color Calculator - How to use?

Discussion in 'Color: Film, Paper, and Chemistry' started by kb3lms, May 5, 2012.

  1. kb3lms

    kb3lms Subscriber

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    I received a "Chromega Subtractive Color Calculator" along with some other darkroom things I purchased. Everything appears to be in the box (actually it appears unused) except for the instructions. How does one go about using this device to get your color balance? I am about to start printing again and would like to try it out.

    Thanks!
     
  2. Cruzingoose

    Cruzingoose Member

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    It is very easy to use.....

    *With the negative you want to print in the enlarger, set your timer for 10 or 15 seconds, and lens at F5.6.
    *Put the diffuser under the lens, in the holder if you have it.
    *Place the calculator on top of the paper, centered.
    *Start your timer and make your exposure. Develop as normal.
    *You will have a series of color squares. Using the gray plastic with punched holes to find the grayest patch. If you have a match, add or subtract filters as indicated on the top and side intersecting rows. If the print is too light or dark, adjust exposure.
     
  3. Mike Wilde

    Mike Wilde Member

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    The only thing I would add is to make sure your start with the recommended filter pack.

    Staring from no filters you will be printing a fair number of iterations to get close to true colours.

    The other thing that the device can fail by is what is know as 'subject failure'.
    Most scenes shot outside will integrate to grey when diffused.
    Scenes with a large preponderence of one colour do not integrate to grey.

    Your best tool here is to make a habit to shoot a grey card on the film you work with, and project it to calibrate filteration.
    When I started to print my own colour I shot a grey card on each different type of film I shot.
    It need not be in focus, but should fill most of the frame.
    I would hold a 4x5 grey card dragged from the camer bag out at arms length, and let light fall on it the way that the light was illuminating the rest of the frame, usually mid day pointed towards the northern sky.

    No diffusion is needed when analysing using a grey card as the negative subject matter, other than you should to account for light fall off in the density judgement patches that presume a diffuser is in use.
    You then have the actual grey card colur reference to compare print hues against as an added check on colour.

    It sounds rinky dink, but shooting a grey card with each film is actually a powerful tool to help you learn to print colour a lot easier.

    Also be aware the dye colours in the calculator may have shifted though the years.

    I have two of these; one by Unicolour and one by Kodak, and they disagree by about 5-10cc in a couple of directions of filtration but not in others.