Question: I’ve heard the term metering but I don’t know what it does and why it’s important. Can you explain what it is?
Answer: When shooting in auto or the semiautomatic modes, your camera has to estimate one or more settings to give you the most balanced possible exposure. It does this by intelligently analysing the intensity of the light that comes down the lens and reaches the sensor. Metering is also active in manual mode, though this is purely to provide you with a lightmeter reading. The problem is, most scenes have a wide variety of light levels that go from deep shadows to bright highlights, so the camera often has a really difficult job producing an accurate overall exposure. Let’s imagine you’re shooting an indoor portrait against a bright window, for example.
The camera doesn’t know whether you want a perfectly exposed face with a blown out background or whether you’re actually going for a silhouette effect.
Understand metering modes
To help your camera make the most accurate possible exposures, all DSLRs, CSCs and serious compacts have several metering modes you can choose from to suit different shooting conditions. They work either by considering light from across the whole frame, or by placing greater or complete emphasis on one specific part. Once you know what these modes do, and when to use them, you’ll be able to get much more accurate exposures in any shooting situation. Let’s check out the four most common metering modes in more detail.
Metering modes - which one to use when...
This is usually the default metering mode for most cameras, taking light into account from across the whole frame. It places greater emphasis on the active focus point, as this is the area you’re most likely to want exposed correctly.
As with evaluative metering, the camera takes into account light from across the whole frame, but with more importance placed on the central area. The active AF point isn’t taken into account, so a bright or dark focal point is less likely to affect your exposure.
Partial metering is similar to spot, but takes into account around 10% of the frame area, ignoring the other 90%. The active area usually follows the active focus point. This mode is ideal for making sure the subject on your active AF point is correctly exposed.
This very precise mode takes readings from around 3% of the frame area, ignoring the other 97%. On most cameras, this area immediately surrounds the active AF point. Spot metering is often used for portraits, though its results are very unpredictable.