Choosing an Exposure Metering Mode with a Nikon D5100
To fully interpret what the exposure meter on your Nikon D5100 tells you, you need to know which metering mode is active. The metering mode determines which part of the frame the camera analyzes to calculate the proper exposure. The metering mode affects the exposure-meter reading as well as the exposure settings that the camera chooses in the fully automatic shooting modes (Auto, Auto Flash Off, and the Scene modes) as well as in the semi-auto modes (P, S, and A).
Your D5100 offers three metering modes:
Matrix: The camera analyzes the entire frame and then selects an exposure that’s designed to produce a balanced exposure.
Your camera manual refers to this mode as 3D Color Matrix II, which is the label that Nikon created to describe the specific technology used in this mode.
Center-weighted: The camera bases exposure on the entire frame but puts extra emphasis on the center of the frame.
Spot: In this mode, the camera bases exposure entirely on a circular area that’s about 3.5mm in diameter, or about 2.5 percent of the frame. The exact location used for this pin-point metering depends on an autofocusing option called the AF-Area mode, which determines which of the camera’s 11 focus points the autofocusing system uses to establish focus.
Because of this autofocus/autoexposure relationship, it’s best to switch to one of the AF-Area modes that allow focus-point selection when you want to use spot metering. In the Auto Area mode, exposure may be incorrect if you compose your shot so that the subject isn’t at the center of the frame.
Matrix metering is the default setting, and you can change the metering mode only in the P, S, A, and M exposure modes. Make your selection via the Quick Settings display. (Press the Info Edit button once to bring up the Shooting Information display and a second time to shift to the Quick Settings screen.)
In theory, the best practice is to check the metering mode before you shoot and choose the one that best matches your exposure goals. Until you’re really comfortable with all the other controls on your camera, just stick with the default setting, which is matrix metering. That mode produces good results in most situations, and after all, you can see in the monitor whether you disagree with how the camera metered or exposed the image and simply reshoot after adjusting the exposure settings to your liking. This option makes the whole metering mode issue a lot less critical than it is when you shoot with film.