Using a gray card.

Discussion in 'Beyond the Basics' started by NEPats37, May 1, 2007.

  1. NEPats37

    NEPats37 TPF Noob!

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    Well I've never used a gray card before and had a few questions. I'll be using it during an air show in order to avoid under exposing the planes. So I simply wanted to know when metering the gray card do I hold it in the same light as the plane will be in. For example if the plane is in a really bright sky do I try to get the gray card in the same light.
    I also read that you should increase exposure by +0.5 stops from the reading you get from the gray card. Is this true?
    Thanks
     
  2. spazoid1965

    spazoid1965 TPF Noob!

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    I would get the light reading off the grey card in as close to the same light as you will be photographing. I wouldn't increase the exposure from that reading. Airshow photos can be very tricky. If it's a bright day you will have heavy shadows on the undersides of the planes.
     
  3. JDP

    JDP TPF Noob!

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    Basically yeah, that's how you do it. Place the card in the same light that you will be shooting your subject in. You could always try locking the exposure of the blue sky and see how that works. There's a book by Bryan Peterson called 'Understanding Exposure' and it's a great reference, check it out.
     
  4. Flash Harry

    Flash Harry TPF Noob!

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    Lock exposure of blue sky will underexpose the planes, try locking exposure on the grass or take your reading for the sky and overexpose by three to four stops, especially if this is neg film and real bright skys.H
     
  5. NEPats37

    NEPats37 TPF Noob!

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    thanks for the replies.
    Any other suggestions for the airshow?
    thanks
     
  6. EOS_JD

    EOS_JD TPF Noob!

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    Perhaps I'm wrong here but I thought a grey card was not used to determine exposure. It's used for colour balancing your images. Setting the white balance using the grey card will mean all your images will not be affected by the colour of the light....

    When metering a grey card, you'd still need to add exposure compensation (as we spoke about in the previous post) if it's being placed against a bright sky....

    Regards
    Jim
     
  7. Torus34

    Torus34 No longer a newbie, moving up!

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    I'm sorry that I can't provide an iron-clad ideal exposure for your situation -- the best I can do is to try to provide an understanding of grey card use.

    Forget color for a moment and think in terms of b&w. A good b&w negative has a range of greys going from almost clear to almost full black. The middle of that range is called 18% grey. That's the same grey as a grey card. If you hold a grey card so that the light which falls upon your photographic subject falls on the grey card, and if you take a reading of the grey card with an accurate exposure meter, you'll get an exposure recommendation. If you use that exposure recommendation and photograph the grey card itself, the developed negative will be [Yup, you guessed it!] middle or 18% grey.

    But what will happen if you use the reading from the grey card to photograph your subject? Those parts of your subject which are the same grey as the 18% card will end up as middle grey on the film. Those parts of your subject which are lighter will end up darker on the film [lighter in the final print.] Those parts of your subject which are darker will end up lighter on the film [darker in the final print.]

    Now let's go to color. Think of colors in terms of pale, light shades and deep, intense shades. A pale color in full light is at one end of the scale. A deep color in shade is at the other end of the scale. But a reading of exposure for the ol' 18% grey card will still end up in the middle of the scale. Colors of medium intensity are the ones that will also end up in the middle of the scale if you use the recommended exposure for the grey card.

    When photographing planes against the sky, the underside of the plane, if in shadow, will be at the dark end of the scale, especially if it's painted a deep color. Parts of the plane in full sunlight, especially if they're reflective silver, will be at the light end of the scale. A light blue sunlit sky will fall toward the lighter end of the scale. White sunlit clouds will also be at the far light end.

    The very best you can hope for will be an overcast day. Light on such a day results in more even lighting and a smaller range of light to dark. A small error in exposure will matter less on overcast days. The grey card reading will probably let you capture all of the color intensities in the scene with room to spare.

    If you have bright sunlight there's a risk that colors in deep shadow will go to black or light colors in full sunlight will go to full white, depending on where you set your exposure. The grey card will tell you which exposure to use for the middle colors to end up in the middle of the film's [sensor's] range, but cannot tell you if you will capture the darkest or lightest colors correctly. If the range of colors seems to be extreme, you can shift a stop or two toward the end of the scale you don't want to lose. That means reducing the total exposure if you don't want to risk losing the lightest shades, or increasing the exposure if you don't want to risk losing the darkest shades.

    Again, I can't provide a single correct answer to your question. The choice will remain yours. If you're using a digital rig with histogram capabilities, you can get a pretty good idea of the range of color intensities in the scene and adjust if necessary.
     
  8. NEPats37

    NEPats37 TPF Noob!

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    wow thanks torus34 that was a awesome answer. one question though. when im metering the grey card do i point it up towards the sky or away from the sky (back of card towards sky)?
    Thanks
     
  9. EOS_JD

    EOS_JD TPF Noob!

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    THe problem is your grey card is NOT in the same light as your subject. (Unless you get it a few hundred feet in the air). Honestly, I say forget the grey card.

    Also I kind of agree that an overcast day for most photography is better than bright sunshine however what images below have more impact?

    This
    [​IMG]

    Or these?

    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]
    Sunny bright days with a nice deep blue sky are better for getting impact on your images. Use exposure compensation to get a correct exposure.#

    Regards
    Jim
     

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