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  1. #51
    Alan Klein's Avatar
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    I've noticed that there is a stop difference between an incident reading and reflected light reading off a gray card all in the same light. Have you guys found the same thing?

  2. #52
    Bill Burk's Avatar
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    That's because the reflected light meter is not calibrated to 18% gray.

    Try metering the palm of your hand and opening up a stop (place on Zone VI). And compare _that_ to an incident reading.

  3. #53
    Alan Klein's Avatar
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    If its not calibrated to 18% gray, why do people use it? What's the point? Exposures are going to be different between reflected and incidence. The answer can't be read the palm of your hand. What if you're black? You should be able to use the meter to get the right exposure with a reflected meter. How do you use a reflected light meter? What is the purpose of the gray card?

  4. #54
    MattKing's Avatar
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    Are you following the directions for the grey card?

    They are quite specific with respect to the angles of incidence.
    Matt

    “Photography is a complex and fluid medium, and its many factors are not applied in simple sequence. Rather, the process may be likened to the art of the juggler in keeping many balls in the air at one time!”

    Ansel Adams, from the introduction to The Negative - The New Ansel Adams Photography Series / Book 2

  5. #55
    Bill Burk's Avatar
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    Alan,

    It's frustrating I know. I think it used to make Ansel Adams mad, and is the basis of a lot of internet discussions.

    The gray card is a "known" reflectance, 18%, from which you take a reading and then calculate the appropriate exposure for an 18% reflectance. Circular reasoning I know.

    The standard calibration of exposure meters, on the other hand, is not an arbitrary or mathematically centered gray. It's not 18%. The exposure meter is actually calibrated to pictures. Scientists studied sets of photographs. They put these photographs in front of people and asked them to pick the best ones. From the research, they established a standard that would lead to a statistically high percentage of successful exposures.

    So you "are supposed to" just point and shoot.

  6. #56
    kintatsu's Avatar
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    Quote Originally Posted by Bill Burk View Post
    That's because the reflected light meter is not calibrated to 18% gray.

    Try metering the palm of your hand and opening up a stop (place on Zone VI). And compare _that_ to an incident reading.
    My understanding was that both types were calibrated the same, modified for some K factor that varies between manufacturers. That K factor is part of the reason we use our working meters in film speed and developing tests.

    It's also possible that some manufacturers use a 12% reference, as that represent middle grey on a scale of 60:1 white to black ratio, and is used by ANSI, if I remember correctly.

    It would seem that measuring incident light would give a higher reading, as you're measuring the light source. It follows that a reflected reading would indicate less light, as the full intensity of the source is not involved. At least, that's my understanding.

    If I'm wrong, I apologize, and am glad to learn something new.
    Last edited by kintatsu; 12-30-2013 at 01:38 AM. Click to view previous post history. Reason: Poor wording

  7. #57
    David Lyga's Avatar
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    There is a case to be made for scrapping that '18%' card and using a '90%' pure white one, instead. That way you get to meter more scenes' ultra low lighting environments. You simply subtract a few stops to then get your actual reading. - David Lyga

  8. #58

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    Quote Originally Posted by David Lyga View Post
    There is a case to be made for scrapping that '18%' card and using a '90%' pure white one, instead. That way you get to meter more scenes' ultra low lighting environments. You simply subtract a few stops to then get your actual reading. - David Lyga
    Or you can just use a LunaPro.

  9. #59
    Alan Klein's Avatar
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    Kintatsu: I believe you're correct. I recall reading about the 12% vs the 18%. But of course, that begs the question. If the meters are set for 12% standard, of what value is using an 18% gray card? Shouldn't we be using a 12% gray card so our reflective and incident readings will match? Does anyone make such a thing?

    E. von Hough: Have you actually tried 18% gray card measurement and incident readings with the Luna Pro in the same light? Do you get the same readings? If so, it appears then that your meter is calibrated to the 18% reading not the industry standard 12%.

  10. #60

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    Quote Originally Posted by Alan Klein View Post
    Kintatsu: I believe you're correct. I recall reading about the 12% vs the 18%. But of course, that begs the question. If the meters are set for 12% standard, of what value is using an 18% gray card? Shouldn't we be using a 12% gray card so our reflective and incident readings will match? Does anyone make such a thing?

    E. von Hough: Have you actually tried 18% gray card measurement and incident readings with the Luna Pro in the same light? Do you get the same readings? If so, it appears then that your meter is calibrated to the 18% reading not the industry standard 12%.
    I was commenting on the Lunapro's low light capabilities, rather than it's calibration.



 

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