An 18 Percent Gray Card is a simple gray-coloured card which uniformly reflects 18% of the light which falls upon it. Gray cards can be used as a reference to set the camera exposure or to calibrate a light meter (light meters are used to determine which exposure setting is required to produce a medium gray tone).
Gray cards are usually made from coated cardboard or polystyrene and come with a protective cover. They are an inexpensive and useful addition to the photographers' kit.
How to Use a Gray Card
To set your exposure with a gray card, first make sure the camera is in manual mode or is able to hold its settings when you half-depress the shutter button.
Position the card immediately in front of the subject, ensuring that the lighting on the card is exactly the same as the lighting on the subject. If you are using a light meter, take your reading now. Otherwise, half-depress the camera shutter button to save the exposure setting until you fully depress the button (and take the picture).
A lot of discussion was then surrounding "over and under" exposing images.
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The point was also that almost all digital cameras are programmed to average out the light in a picture to 18%. Knowing that, we can trick the camera in causing over/under exposure to achieve what we want.
e.g.
If we have an area with large areas of light and dark, and we want to see detail in the dark area, point the camera at the dark area, press the shutter halfway and hold. Move the camera to re-frame the shot, including the lighter area, and press the shutter all the way. The picture will be overexposed, but we get what we want. Isabelle`s architerture shots in this gallery are a perfect example of this.
Bob
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Please feel free to post a maximum of 3 images from our trip!!!
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