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Thread: Grey card wrong?

  1. #11

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    Re: Grey card wrong?

    Quote Originally Posted by ic-racer View Post
    This article looks like a better summary than usual...

  2. #12

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    Re: Grey card wrong?

    Quote Originally Posted by swmcl View Post
    Hello all.

    I got out my Kodak grey card and decided to try something different. I had gone to the local craft shop and purchased a 150mm poly whatever (styrene I think) foam ball. You know, the white ones. I also purchased some cheap acrylic paint in tubes - one white, one black. I mixed up what I thought might be a good shade of grey and painted the ball with it. As it turns out it darkened a little upon drying.

    Then I sat my newly painted but dry (not glossy) ball on a stick and had my daughter hold the Kodak grey card alongside in even but afternoon light ...

    Guess what ? The centre of the ball came up with the same exposure as the incident reading yet the grey card - which does appear lighter and a little glossy I must say - gave a reading 2/3rds of a stop different. I was up pretty close to the ball and card so that the meter was reading in the centre of each.

    I'm using a very new Sekonic L758DR mind you which talks in 1 tenth stops.

    What do you think ? Could the grey card be out ? Should I now paint the grey card and the ball ?!?! Should I just get over it and leave the grey card alone from now on ? Lastly, should I use the grey card as-is but realise it is 2/3rds of a stop out of 'calibration' with my meter ?

    Measurements were within 10 seconds of one another if you're thinking there may be a time factor in it.

    This is not the first time I've queried the grey card mind you. It was out with my other meter too - an L358.

    Rgds,

    Steve
    Your test is flawed from the start. An 18% gray card is middle gray that reflects 18% of the light that illuminates it (18% reflectance). A styrene ball, being porous, will have a much lower reflectance value that 18%. So, using a reflective light meter, I owuld never expect to get the same exposure value when comparing an 18% gray card and a styrene ball (even assuming your styprene ball is really middle gray).

  3. #13

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    Re: Grey card wrong?

    The Kodak Neutral Test Card tells you to hold the card in front of the subject so that it faces half way between the camera and the main light.

    Importantly, it also states (this quote is actually taken from "Kodak Professional Black-and-White Films" but the card instructions say the same): "If you make a reflected-light reading from a gray card with incandescent illumination in the studio, use the exposure indicated by the meter. If you use the gray card to determine exposure outdoors in sunlight, increase the exposure indicated by the meter by 1/2 stop."

    In dimly lit scenes, you can use the 90% white reflectance side, keeping in mind that there is a difference of five stops between your neutral gray and white (18% and 90% reflectance).

  4. #14

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    Re: Grey card wrong?

    Quote Originally Posted by vinny View Post
    2/3 of a stop isn't much unless you're shooting chromes. Then it's a LOT and unnacceptable
    Agreed. What's color?
    Bruce Barlow
    author of "Finely Focused" and "Exercises in Photographic Composition"
    www.brucewbarlow.com

  5. #15
    Kirk Gittings's Avatar
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    Re: Grey card wrong?

    Quote Originally Posted by Bill Burk View Post
    There is plenty of Internet information that explains 18% gray card is not the equivalent of incident mode. Meters are not calibrated to 18%.

    I use the same meter and have the Sekonic gray card which includes patches in 1/3 stop intervals so I can find the patch that does give the same spotmeter reading as incident mode in the same light. I find the reading is closer to 12%, which agrees with correspondence I've had here and on APUG, and it agrees with Internet lore*.

    Instead of confirming exposure with a gray card, I satisfy my "sanity" by taking a spotmeter reading of the palm of my hand. When I "place the reading on Zone VI," my readings agree well with the incident mode, and then I feel more reassured.

    *But of course that doesn't prove the Internet lore is correct.
    However not everyones palm should be placed on ZI as pigmentation varies. Just saying as mine never reads one stop brighter than middle grey. But do I meter off it and place it on ZI in a pinch? You bet. Always gets me in the ballpark. In changing light with rapidly moving clouds etc. It gets me a quick relatively accurate exposure right off. Then for the next exposure I can take more time.
    Thanks,
    Kirk

    at age 73:
    "The woods are lovely, dark and deep,
    But I have promises to keep,
    And miles to go before I sleep,
    And miles to go before I sleep"

  6. #16

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    Re: Grey card wrong?

    Quote Originally Posted by Kirk Gittings View Post
    However not everyones palm should be placed on ZVI as pigmentation varies. Just saying as mine never reads one stop brighter than middle grey.
    Haaa, yes I keep forgetting people differ, and this is just what works for ME.

    swmcl, if reading YOUR palm and placing on ZVI matches the reading from incident mode... Then, like me, you'll have a confidence-building quick check.

    At least you will catch BIG mistakes like incident metering the light falling on your ear when you think you are spotmetering.

    I went through the same doubt when my meter was new, and I was about to remove the K factor from the meter (because you CAN).

    Until I found this much better plan... By USING the Zone System meter-and-place technique to confirm the Incident Mode.

    I gave up the confidence-shaking result of working with a Gray Card and trying to remember the exact relationship.

  7. #17
    8x10, 5x7, 4x5, et al Leigh's Avatar
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    Re: Grey card wrong?

    Quote Originally Posted by Bill Burk View Post
    ...USING the Zone System meter-and-place technique to confirm the Incident Mode.
    Sorry, Bill.

    Incident metering is significantly more accurate in all cases than using the ZS.
    Of course this assumes that you haven't mucked with the meter's calibration.

    The ZS relies on your perception of tonality, which is imperfect even in a highly experienced practitioner.

    The perceived reflectance (tonality or "zone") of a surface varies due to many factors.

    Human perception of reflectance can be influenced by color, angle of incident light, angle of surface to line of sight, and reflectance of adjacent areas.

    It's easy to demonstrate this fact by simply spotmetering a gray card at different angles.
    That's why the instructions tell you to position it quite specifically relative to incident and lens axis.

    - Leigh
    If you believe you can, or you believe you can't... you're right.

  8. #18

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    Re: Grey card wrong?

    Gray cards fade with time and with exposure to UV.

  9. #19
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    Re: Grey card wrong?

    Sounds like apples and oranges in technique. Either paint another flat card and then match the styles of reading, or recognize that you need to do an incident reading rather than a reflective reading from the ball because the shapes between flat and curved, no matter how small an area, change how the light reflects from the curve surface.
    "One of the greatest necessities in America is to discover creative solitude." Carl Sandburg

  10. #20

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    Re: Grey card wrong?

    The card should be oriented such that a line perpendicular to its surface bisects the angle between the light source and the camera.
    Disagree. This maximizes the (unwanted) specular reflection. Use your gray card with sun incident at 45°, and meter staring along perpendicular. Please try and report back.

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