You might want to select a particular metering mode for your first shots, although the default Evaluative Metering (which is set automatically when you choose a Basic Zone mode) is probably the best choice as you get to know your camera. To change metering modes, press the Metering Mode/WB button and spin the Main Dial to cycle among the choices shown in Figure 1.10:
Evaluative metering. The standard metering mode; the 40D attempts to intelligently classify your image and choose the best exposure based on readings from 35 different zones in the frame, with emphasis on the autofocus points.
Partial metering. Exposure is based on a central spot, roughly nine percent of the image area.
Spot metering. Exposure is calculated ...