Digital SLR Camera Metering Modes
Digital SLRs have several ways to measure reflected light. They are called metering modes. Your camera will have three or more modes for you to choose from. They differ in how they evaluate different areas of the scene. One mode takes the entire frame into account. Other modes measure the center or very small spots.
Refer to the figure as you read. The green areas in the viewfinder represent the areas the camera uses when metering in each mode.
When this mode is selected, the camera divides the scene into zones and evaluates the brightness of each separately. Each manufacturer has its own system for how it weighs each area and combines the information into a single overall exposure. Camera manufacturers call their multi-zone metering modes by different names: 3D color matrix metering (Nikon), evaluative metering (Canon), and multi segment metering (Pentax and Sony). You may also hear it referred to as segment or multi-pattern metering.
Multi-zone is a good general-purpose metering mode and is the default for most cameras. You need not switch from it unless you’re dealing with strong backlighting or want to measure light reflecting off of specific objects or areas in the scene.
Center-weighted mode meters the entire frame but gives more weight to elements in the center than around the edges. Though the bias varies, it’s in the range of 70 percent center to 30 percent edges. Canon refers to this as center-weighted average metering mode.
Center-weighted metering is a good mode for portraits and other photos with relatively large subjects in the center of the frame.
Spot metering measures light in a small circle in the center of the frame and ignores everything else. This metering mode is useful if you need to measure reflected light from a specific object or point in the scene. Some cameras let you change the size of the spot circle. Canon has an extra mode that covers a larger central area, called partial metering. Some cameras (more expensive Nikon models) enable you to link the spot meter to the current AF point, which is very handy.
Spot metering is good when you want the camera to calculate the exposure from a very precise spot in the scene. This can be your main subject, or an object that you don’t want under or overexposed.