Metering Modes: Getting Your Exposure Right
Whenever your camera isn’t in full manual mode, it measures the amount of light reflected from the scene (a process called ‘metering’) and uses inbuilt algorithms to decide how to set the aperture, shutter speed and/or ISO.
The camera doesn’t understand what exactly you are trying to capture, so by default chooses exposure settings that result in the tones in the image averaging to a mid-grey tone. Adjusting the metering mode changes which parts of the image frame the camera meters from, which is particularly useful when photographing a scene that is backlit or high contrast.
For example, if you were shooting portraits on a bright, snowy day, with pure white scenes behind your subject, the camera would underexpose the scene in order to render those white tones as mid-gray. If you were photographing a dark-skinned subject wearing dark clothes on a dark background, the camera would compensate for all those heavy tones by overexposing the image.
Equally, if your scene is high contrast, with a light subject in front of a dark background or vice versa, the camera’s default metering mode is likely to get the exposure wrong. Here’s what the different settings mean:
This setting is known by several names: evaluative metering – Canon; matrix metering – Nikon; and multi-segment metering – Sony. It is the default metering mode on most DSLRs, and uses light readings from multiple areas across the frame, biasing the exposure settings depending on which area of the frame which has the focus point selected. Although this mode works well on most low-contrast scenes, it can let you down when there are extremes of light and dark tones. Using exposure compensation is a quick and easy way of compensating for over- or underexposure when using this mode.
In this mode, the camera meters from a large proportion of the frame, but with a bias towards rendering the central tones as an average mid-gray. It works well when your subject is in the middle of the viewfinder. Unlike multi-zone metering, it doesn’t take into account which area of the image is in focus.
This mode takes the light readings from as little as 2% of the frame, only taking into account a small area in the very centre. This mode is ideal for high contrast scenes. Don’t worry if you don’t want your subject to be in the exact middle of the frame in the final image; push the shutter release halfway down while the central focus area is on your subject’s face (or nearest eye), then hold it there while you reframe your shot, before pressing all the way to take it.
This mode is similar to the spot metering mode, but instead measures the amount of reflected light from a slightly larger central area, roughly equivalent to about 10% of the whole frame. Like spot metering, this mode is useful when there are extremes of light and dark tones in a scene, but would be used when the key area of the image – usually your subject’s face – is slightly larger in the frame.
The area that you are metering from needs to be a mid-tone, otherwise the camera will under- or overexpose the scene. When using center-weighted, spot or partial metering, you may need to frame the shot differently at first to make sure that a mid-tone is in the center while the camera takes the meter readings. When you press the shutter release button halfway, the exposure settings are locked until the button is pressed fully.
This means that you can quickly reframe your shot before pushing the shutter release all the way. Alternatively, or if you want to meter from a part of the scene that you don’t want to also focus from, look for a button marked ‘AE-L’, which stands for Automatic Exposure Lock, and press this before focusing your shot.