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Gray card

A handy exposure tool for the digital or film photographer.


A reflected-light meter reading off a gray card that's in the same light as your subject will provide proper exposure.
A reflected-light meter reading off a gray card that's in the same light as your subject will provide proper exposure.

Most scenes and subjects reflect an overall average of about 18% of the light that strikes them. This is why exposure meters that read reflected light, such as the light meter built into a camera, are calibrated to provide accurate exposure settings for subjects that reflect 18% of the light striking them. If a subject reflects more or less than 18% of the light, the reflected light meter reading will provide settings that under-expose or over-expose the subject. Scenes that have a great deal of snow or sand in bright sunshine are typically problematic for a reflected-light meter, as are scenes that contain large, dark areas. But average scenes containing grass, foliage, neutral-colored clothing and other mid-tones usually compare closely to the average 18% reflectance.

When a camera’s light meter is aimed at a scene that contains large areas that are unusually bright or unusually dark, its readings tend to render these subjects as if they were less bright or less dark. So bright, white snow in a scene will be photographed as if it were gray, and a black shadow area will also be rendered on film or your digital camera's sensor as gray when you use the meter’s recommended exposure settings. You can get around this problem with very bright scenes by manually increasing exposure (a wider aperture or a slower shutter speed). You would decrease exposure (a smaller aperture or faster shutter speed) when you want dark areas to look black, not light gray.


HOW MUCH SHOULD I CHANGE EXPOSURE?

When a scene doesn’t have average illumination, you can guess. When shooting bright snow, for example, an exposure increase of around two stops will generally provide proper exposure, and your snow should look naturally white, not gray.

USE A GRAY CARD FOR A REALLY ACCURATE EXPOSURE READING

For real accuracy, however, you can take a “substitute reading” off a gray card that is placed in the same light as your subject.

WHAT IS A GRAY CARD?

Also known as the Kodak neutral test card, a gray card is an 8" X 10" sturdy card, about 1/8" thick. It is uniformly gray on one side, which reflects precisely 18% of the white light that strikes it (corresponding to the calibration of a reflected-light meter), and uniformly white on the other, which reflects 90% of the light. (Using metric measurement, the card is a little over 20 cm by 25.5 cm in size.) You can purchase a gray card from just about any photography retailer.

If you rely on your camera's built-in meter for proper exposure of a bright snow scene, snow turns out looking gray instead of white.
If you rely on your camera's built-in meter for proper exposure of a bright snow scene, snow turns out looking gray instead of white.

A gray card is useful for obtaining proper exposure of bright snow scenes.
A gray card is useful for obtaining proper exposure of bright snow scenes.

HOW DO I USE A GRAY CARD?

(1) Hold the card in the same light that is falling upon the area of the scene that you wish to be properly-exposed.
(2) Be sure that the gray face of the card is directed straight at the camera position.
(3) Point your light meter (or camera lens if using a built-in light meter) directly at the face of the card.
(4) Be sure the card is close enough so that the light meter reads only the light reflected from it. If you are looking through the lens, bring the card so close that it occupies the entire viewframe.
(5) Take a light meter reading, and use the resulting exposure settings to photograph your subject, which will now be properly-exposed.


THE WHITE SIDE OF A GRAY CARD

When there is insufficient light for you to take a reliable meter reading from the gray side, use the white side, and multiply the exposure given by 5. Why 5? Because the white side reflects five times as much light as the gray side (90% versus 18%).

The white side of a gray card can also be quite useful as a reflector for bouncing flash onto your subject. (See our section entitled “Bounce flash”)

The white side of a gray card has practical uses, too.
The white side of a gray card has practical uses, too.

Any scene that contains a wide expanse of white can trick your camera's meter.
Any scene that contains a wide expanse of white can trick your camera's meter.

REPLACE YOUR GRAY CARD PERIODICALLY

You will find that a gray card that gets frequent use may become soiled or scratched over time, or may fade, particularly when improperly-stored. A good indicator of its condition is the white side, because deterioration shows up better. If its white side has become yellowed, it's time to get a new one. You can also have a look at a new gray card next time you're in a camera store, and compare it with your own gray card. If you see differences, better buy a pristine replacement to avoid inaccurate exposure readings.


A HANDY LITTLE GRAY CARD

For those of you who may have purchased our popular, handy and unique "Guide to Posing the Female Model" book, you will have noticed that it has a gray card conveniently printed on the inside back cover.

It is a handy place for it, easy to use and always available.

The inside back cover of the popular PhotographyTips.com
The inside back cover of the popular PhotographyTips.com "Guide to Posing the Female Model" book is a gray card.
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