Using Metering Modes
In photography, the metering mode refers to the way in which a camera determines exposure. The most common metering modes are spot, center-weighted and multi-zone/matrix metering modes.
The camera will measure on a very small area of the scene – about 1-5% of the viewfinder. By default, this is the center of the scene, but the photographer can select a different spot. Spot metering is not influenced by other areas in the frame. It is commonly used to shoot a high contrast scene, such as a backlit situation, when the photographer would want to expose a person’s face properly. Letting the camera evaluate the scene would result in under-exposure of the person’s face.
The meter concentrates on the central 60-80% of the scene. The balance “feathers” out towards the edges, giving no weighting to any particular portion of the metered area. This mode is best used for objects of interest in the center of the frame. Some cameras will allow the focus point to be moved off the image center, and the metering will occur around the new focus point.
This is the default setting for most cameras. The camera measures the light intensity in several points in the scene and then combines the results to find the setting for the best exposure. The design concept behind Evaluative/Matrix Metering is to reduce the need to exposure compensation.