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  1. #11
    Lee L's Avatar
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    Quote Originally Posted by Leigh B View Post
    However, its measurement is accomplished by analyzing the red and blue components of the spectrum with absolutely no regard to green
    You are conflating what Gossen does specific to metering color balance for photography with the definition of color temperature, and assuming that their method is the only one used. Gossen chooses one way to do it that works well with three layer color film, and their meter does measure green relative to magenta (a mix of both blue and red). Their method isn't the only way to measure color temperature.

    However, your statements about measuring color temp with only blue and red, disregarding green are simply wrong, and misleading.

    Astronomers measure color temperature with Ultraviolet, Blue, and Visible (green-yellow) passband filters, that don't reach deep into red. And yes, they do use green wavelengths as a component to measure color temperature. That's where the V component filter peaks in sensitivity.

    You can also use a spectrograph to measure color temperature, which includes green components.

    It's nice that you taught color theory. My mom, who is an artist, taught me additive and subtractive color theory when I was a child. I've also used a Minolta color meter for commercial/advertizing photography on location and in the studio.

    I also wrote and taught curriculum for physics labs on color temperature at a top ranked college, which was reviewed and also taught by physicists with Ph.D.s from Cornell and U.C. Santa Barbara.

    You should recognize that there is more than one way to measure color temp, and that stating that it's always and only a blue-red ratio is wrong.

    Lee

  2. #12
    Leigh B's Avatar
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    Quote Originally Posted by Lee L View Post
    However, your statements about measuring color temp with only blue and red, disregarding green are simply wrong, and misleading.
    Astronomers measure color temperature with Ultraviolet, Blue, and Visible (green-yellow) passband filters, that don't reach deep into red. And yes, they do use green wavelengths as a component to measure color temperature. That's where the V component filter peaks in sensitivity.
    I also wrote and taught curriculum for physics labs on color temperature at a top ranked college...
    You should recognize that there is more than one way to measure color temp, and that stating that it's always and only a blue-red ratio is wrong.
    You'll forgive me for presenting an answer that's relevant specifically to photography.

    This is after all a photography forum, not one for astronomers or physicists.

    Since you appear to be well-versed in the theory, you should know that the "color temperature" of any visible black-body spectrum can be calculated by comparing the amplitudes at any two points on the curve. Accuracy is enhanced by choosing two points that are as far apart as possible in wavelength (i.e. color).

    It's convenient and less expensive from a manufacturing standpoint to measure red and blue components and compare them. This DOES NOT include green, which is measured separately if at all.

    We're dealing with visible light here, with CT in the range roughly 2500° to 6500° k.

    Photographers don't care about UV.

    - Leigh

  3. #13
    olleorama's Avatar
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    Reminds me of this:


  4. #14
    Lee L's Avatar
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    Quote Originally Posted by Leigh B View Post
    Photographers don't care about UV.
    That must be why no one manufactures or buys UV filters for camera lenses.

    Lee

  5. #15
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    Quote Originally Posted by Lee L View Post
    That must be why no one manufactures or buys UV filters for camera lenses.
    Are we to be perpetually bombarded by your nonsensical remarks?

    My comment was in the context of color temperature calculation, as a rebuttal to your mention of UV measurements being used for that purpose.

    As to UV filters, they're sold and used primarily as physical protection for the front element of the lens, not for their attenuation characteristics.

    - Leigh

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