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Saturday, January 17, 2009

Meter from a Middle Tone

You probably know this already, but all light meters are designed to give accurate readings only when metering a subject of average tone. This is often referred to as "middle gray" because an average tone sits in the middle of a tonal gray scale halfway between pure white and pure black. If you're not reading from a middle tone, your light readings can never be accurate--unless you make exposure adjustments (using "exposure compensation," for example) based on personal experience.

It's far simpler to find an area within your scene that is of a middle or "average" tonality. Fortunately these things are quite prevalent--green foliage, green grass, blue sky, most gray objects--are close enough to middle gray in tone to provide very accurate metering results. This is particularly useful when a scene contains a lot of very bright subject matter (like the snow in this scene) or very dark areas (big shadow areas or a dark-colored building, for example) because these dark or light areas will fool the meter. But if you meter from the neutral/average tonal area, the light or dark areas where fall exactly where they belong.

Careful metering is important and it's why your camera probably has a center-weighted metering mode--so that you can choose what to meter precisely. In that mode your meter is concentrating almost all of its metering attention on a small area in the center of the frame (indicated in your viewfinder by a circle in the center). And once you've metered the best area, simply use your meter-lock feature (holding the shutter-release button down halfway) to lock that reading and your exposures will be perfect. For more on the theory and practical uses of light metering, be sure to see my latest book Exposure Photo Workshop--hopefully your local library has a copy so you can borrow it for free.

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