Canon PowerShot G12, Metering Modes for Portraits

For most portrait situations, the Evaluative metering mode works well. (For more on how metering works, see the “Metering Basics” sidebar.) This mode measures light values from all portions of the viewfinder and then establishes a proper exposure for the scene. The only problem that you might encounter when using this metering mode is when you have very light or dark backgrounds in your portrait shots.

In these instances, the meter might be fooled into using the wrong exposure information because it will try to lighten or darken the entire scene based on the prominence of dark or light areas (Figure 6.2). You can deal with this in one of two ways. Or, you can change the metering mode from Evaluative to Spot metering. The Spot metering mode uses only the center area of the viewfinder to get its exposure information (Figure 6.3). This mode is also great to use when the subject is strongly backlit.

Figure 6.2 The light background color fooled the meter into choosing a slightly underexposed setting for the photo.

Figure 6.3 When I switched to the Spot metering mode, I was able to specify the woman as the metering target, which made the camera adjust the aperture.

Metering Basics

You camera has multiple metering modes, but the way they work is very similar. A light meter measures the amount of light being reflected off your subject and then renders a suggested exposure value based on the brightness of the subject and the ISO setting of the sensor. To establish this value, the meter averages all of the brightness values to come up with a middle tone, sometimes referred to as 18 percent gray. The exposure value is then rendered based on this middle gray value. This means that a white wall would be underexposed and a black wall would be overexposed in an effort to make each one appear gray. To assist with special lighting situations, the G12 has three metering modes: Evaluative (Figure 6.4), which uses the entire frame; Center-Weighted Average (Figure 6.5), which looks at the entire frame but places most of the exposure emphasis on the center of the frame; and Spot (Figure 6.6), which takes specific readings from small areas (often used with a gray card).

Figure 6.4 The Evaluative metering mode uses the entire frame.

Figure 6.5 The Center-Weighted metering mode looks at the entire frame but emphasizes the center of it.

Figure 6.6 The Spot metering mode uses a very small area of the frame.

Setting your metering mode to Spot metering

Press the Metering Light button, located at the upper right of the Control dial.
Use the Control dial to scroll through the metering modes until you find the symbol for Spot metering mode.
Press the Metering Light button to return to shooting mode.