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  1. #11
    PeterB's Avatar
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    Thanks for the additional replies. There were two important lessons I learnt from this thread.

    1. It is up to the photographer to place "darker" colours on lower zones, lest they be rendered the same shade as "lighter" colours.
    2. Light meters, panchromatic film and our eyes all have different spectral sensitivity curves. Refer to the following excerpt from p.190 of WBM Ed.2, Copyright 2011 Ralph W. Lambrecht, Chris Woodhouse (I'm satisfied I followed the "fair use" rules).

    Attached Thumbnails Attached Thumbnails Sectral Sensitivities of a film a meter and an eye. Copyright WBM Ed.2 p.190.jpg  

  2. #12
    RalphLambrecht's Avatar
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    Quote Originally Posted by PeterB View Post
    I have searched for hours trying to find the answer to this question.

    In the Zone System (for B&W) - why is the colour of the spot metered area unimportant?

    A hypothetical example - the reflectivity of indigo is much less than yellow. If I had two scenes , one with indigo in a shadow, the other with yellow in shadow (same incident light level to both colours) and I wanted to place them both in zone III, they will both turn out to be the same shade of grey. That isn't good since I'd like the indigo to be darker than the yellow.

    What am I missing ??!!
    the snswer is in the different spectralse sitivitiest of film ,meter and the human eye
    Attached Thumbnails Attached Thumbnails SpectralSensitivityMeter.jpg  
    Regards

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

  3. #13
    Stephen Benskin's Avatar
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    Quote Originally Posted by PeterB View Post
    A hypothetical example - the reflectivity of indigo is much less than yellow. If I had two scenes , one with indigo in a shadow, the other with yellow in shadow (same incident light level to both colours) and I wanted to place them both in zone III, they will both turn out to be the same shade of grey. That isn't good since I'd like the indigo to be darker than the yellow.
    Peter, I know what you are talking about, but you've stated it incorrectly. If the reflectance is different for two objects under the same illuminance, they will have different luminances; and barring any spectral sensitivity problems, the resulting exposure will produce different densities. What you're talking about is producing different tones from two objects of different colors having the same luminance.

    As Bill said, color filters are the answer. I've attached the Maxwell Triangle which "can be used to predict the effect of color filters on black and white film." As the color of the filter moves further from the subject's color, the resulting tone progressively darkens. Complementary colors darken. Supplementary colors lighten.
    Attached Thumbnails Attached Thumbnails Maxwell Triangle.jpg  

  4. #14
    Leigh B's Avatar
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    All(?) modern exposure meters incorporate filtration to match the response to that of "average" photographic film.

    The native sensitivity curves of silicon or selenium are not relevant.

    - Leigh
    “Wise men talk because they have something to say; fools, because they have to say something.” - Plato

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