Determining the Correct Exposure

When Daniel was in high school, one of his most precious possessions was a cigarette-pack-sized Weston III light meter. It was a very expensive professional photographer's tool for reading the light of a scene and determining the appropriate exposure—so expensive for a 15-year old kid that he bought it used. Daniel carried that Weston meter everywhere he went, whether or not he had a camera along with him. At every opportunity, in good weather or bad, sunrise or twilight, he would whip it out and take a reading of the light, training himself to recognize the correct combinations of f-stops and shutter speeds. Sounds sort of geeky for a kid, but he still retains the uncanny ability to look at a scene and know the correct exposure settings he'll need to take a perfect picture.

Sally prefers to simply use a light meter and concentrate on her composition. After all, that's what the devices are for.

Digital cameras have sophisticated and highly intelligent light meters built into them that make the Weston seem downright primitive. Turn on your camera, point the lens at your subject, press the shutter button halfway down, and the internal meter will read the scene and set (or suggest) the appropriate settings.

For most consumer digital cameras, all this is done automatically, especially if you are in the default point-and-shoot mode. However, prosumer and professional cameras have various metering options urn that you can choose, depending on how even the lighting conditions are. Why bother, you ask? Because more accurate light readings can lead directly to better exposures and superior images that need little or no image-editing corrections.

The most common metering choices are:

■ Matrix metering—Matrix reads several areas throughout the scene and averages their values. Many (but not all) digital cameras use matrix metering as their default setting. When the lighting in a scene is somewhat even, and when no specific area needs a greater attention than others, this is generally the best all-around mode.

■ Spot metering—Spot takes its exposure reading from a small section in the middle of your frame, often marked in the viewfinder by a circle or square brackets. Use spot metering when you want to be sure that a certain small area of your picture is properly exposed, such as a portion of a face falling in shadow or backlit. (See Figures 6-8a and 6-8b.)

■ Center-weighted metering—Center weighted reads the lighting conditions in the general area of the center of your frame, with input from the corners as well. A good compromise between matrix and spot, center weighted is the preferred mode for portraits and other compositions in which the main subject fills a significant portion of the frame.

In more advanced cameras, you can actually move around the center of the area you wish to meter, creating your own weighting of what portion of your photo you are most concerned about being properly exposed. If your camera has this capability, play around with it for a fun learning experience.

Figure 6-8a: Daylight streaming in behind the toy leopard skews the auto-exposure settings to the background, making the leopard too dark.

Figure 6-8b: By taking a spot meter reading on a shadow in the leopard's face, locking down the exposure, then composing and shooting, we get a better exposure. However, the best solution for this photo (so both the background and the leopard would be well exposed) would be to use a fill flash. (See Chapter 9.)

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