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  1. #1

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    Why don't reflective meter reading of zone V card and an incident reading match?

    Trying to calibrate exposure, film and dev with meter and wedge step:

    I thought I already understood this well but now I'm getting confusing results.

    Equipment:

    Stoufer RZ1 (with zones)
    Weston Master V meter with diffusion cone
    Kodak 18%

    The Kodak 18% grey matches zone V on the Stouffer step wedge. As I thought.

    If I take an incident reading with the cone on I get exposure value 8.

    Then if I take a reflective reading using the card, I get a full stop difference at exposure value 9.

    I have assumed for years that incident readings taken with my meter would give an exposure for equivalent of a zone V card reflective reading. Am I wrong?

    Which is the true mid-grey (V) exposure?

  2. #2
    Bill Burk's Avatar
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    The incident reading is calibrated to the dome itself.

    The 18% gray card is a "known reflectance" that is suitable for determining exposure - but from what I gather and am starting to believe... It's NOT what the reflected light meter is calibrated to.

  3. #3
    MattKing's Avatar
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    Did you read the instructions that go with the gray card?

    I ask, because very few seem to read them.

    The angle you hold the card is important - if done properly, it will tend to give a reading that is about 1/2 stop less than reading the card "straight on".
    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

  4. #4
    johnnywalker's Avatar
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    I've never had any luck getting them to read the same. Even after reading the instructions, I've decided it's all in the way you hold your tongue.
    If I had been present at the creation, I would have given some useful hints for the better arrangement of the Universe.
    Alfonso the Wise, 1221-1284

  5. #5
    Bill Burk's Avatar
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    That's why I held my tongue.

    Yesterday I was experimenting with flare. In a backlit scene, with lots of flare, I aimed spotmeter at graycard and it measured same as incident mode... when I was close enough with the spotmeter to minimize flare. When I backed away enough to induce flare, my spotmeter reading went up a stop.

    In a low flare situation, the two modes agreed.

  6. #6
    bobwysiwyg's Avatar
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    Quote Originally Posted by johnnywalker View Post
    I've never had any luck getting them to read the same. Even after reading the instructions, I've decided it's all in the way you hold your tongue.
    I tend to agree.
    WYSIWYG - At least that's my goal.

    Portfolio-http://apug.org/forums/portfolios.php?u=25518

  7. #7

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    Quote Originally Posted by MattKing View Post
    Did you read the instructions that go with the gray card?

    I ask, because very few seem to read them.

    The angle you hold the card is important - if done properly, it will tend to give a reading that is about 1/2 stop less than reading the card "straight on".
    I knew you had to hold it at angle (1/3 towards camera axis) but this gives around 1/4 to 1/3 stop difference for me. That counts for a bit but still around 2/3 stop out.

  8. #8

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    Quote Originally Posted by Bill Burk View Post
    The incident reading is calibrated to the dome itself.

    The 18% gray card is a "known reflectance" that is suitable for determining exposure - but from what I gather and am starting to believe... It's NOT what the reflected light meter is calibrated to.
    Bill, so are you suggesting that the incident reading with dome is a more reliable method? i.e independent of tongue locations?

  9. #9
    markbarendt's Avatar
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    It is a pretty safe assumption that the incident meter is "right" as far as the ISO standard.

    When using any target in the scene it is important that it be used in a consistent manner and that you know what the offset is.

    The grey card, as Bill indicated, isn't necessarily a match for the ISO standard.

    Take a reading with the incident meter then with any target in that same spot, take a reflected reading with your spot meter. The difference is the offset you need to use for that target.
    Mark Barendt, Ignacio, CO

    "We do not see things the way they are. We see things the way we are." Anaïs Nin

  10. #10
    Bill Burk's Avatar
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    There are techniques for holding the incident meter as well (towards the light vs towards the camera) that can affect the result too.

    But in general, I think the incident meter gives you a direct calculation that you are able to use directly off the calculator dial, while the 18% gray card gives you a reading that you are supposed to adjust.

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