Evaluative metering
Evaluative metering is the default metering mode on the Rebel XSi/450D, and it analyzes light from 35 zones throughout the entire viewfinder and links it to the autofocus system. The meter analyzes the point of focus and automatically applies compensation if the surrounding areas are much lighter or darker than the point of focus. To determine exposure, the camera analyzes subject position, brightness, background, front- and backlighting, and camera orientation.
2.10 This image was taken using Evaluative metering. Subsequent images show the same subject in different metering modes. Exposure: ISO 100, f/6.3, 1/5 second.
Evaluative metering produces excellent exposures in average scenes that include a distribution of light, medium, and dark tones. However, in scenes where there is a large expanse of predominantly light or dark areas, the metering averages the tones to middle gray, thereby rendering snow scenes and large expanses of dark water as gray. In these situations, it's good to use Exposure compensation to increase or decrease exposure by one to two stops for scenes with predominantly light or dark tones, respectively.
Note Evaluative metering mode is the default for all Basic Zone modes.
To select Evaluative metering mode, set the camera to a Creative Zone mode, press the Metering mode (top cross) key on the back of the camera, and then press the up or down cross key to select the icon showing a solid dot within a circle within a rectangle.
Note ^ pictures are slightly underexposed, the camera automatically corrects them using Auto Lighting Optimizer. This optimization is applied to all images taken in Basic Zone modes, and to JPEG images taken in Creative Zone modes other than M mode. Optimization is handy if you print directly from the media card. But if you prefer to see the original exposure, you can turn off the optimization by disabling C.Fn-6. See Chapter 5 for details on Custom Functions.
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