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Thread: mcds

  1. #1

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    mcds

    Does anyone know offhand if mcds are a purely physical measurement...
    or, a psychophysical measurement?

    I think its the former but want to double check.

    Ray

  2. #2

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    Somewhere in between. The measurement is weighted by a model of the spectral response of the human eye, so it depends on colour.

    http://en.wikipedia.org/wiki/Candela

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    Thanks.

    Guess I'm a bit confused about how light meters work...
    are those readings also biased in favor of human vision?

    If you illuminate a subject in green light vs Blue or Red, is there an intentional bias in the meters logic?

    What is the purely non-psychophysical measurement of light for photographic purposes?

  4. #4
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    1⁄683 watt per steradian of green light is pretty much set in stone since 1979. It is a purely physical measurement.

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    Quote Originally Posted by ic-racer View Post
    1⁄683 watt per steradian of green light is pretty much set in stone since 1979. It is a purely physical measurement.
    Does that 1⁄683 watt per steradian apply to all wavelengths?

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    Quote Originally Posted by Ray Rogers View Post
    Does that 1⁄683 watt per steradian apply to all wavelengths?
    No. only visible light which is peaked in the green.

  7. #7

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    Ok, so the different wavelengths are weighted differently... in mcd;

    Jumping from mcd to photographic light meters, is this also true of light meters?

    or do they use a purely physical measurement?



 

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