The Metering Matter - A Weighty Issue
20 June 2008

Exposure is so important that it's gone beyond the simple matter of how much light is getting through. Cameras these days come with an important exposure metering system that carefully calculates the correct exposure for the image based on the parameters you set. Should it concentrate on your subject in the middle? Or the whole area? It's one of those computing smart features that tirelessly calculates and recalculates the exposure to fine tune it, depending on if you are zooming into something or have a filter over the lens. Whether you are using the auto mode, shutter or aperture priority mode or manual mode it's a good idea to choose a metering system to suit the situation.

Centre Weighted
In this mode, the camera puts the emphasis on the centre of the frame which means it measures the exposure information from the light that's coming through the middle of the frame though it still takes some data from the rest of the frame. This is good for situations where your most important subject is in the centre of the frame such as portraits or you are taking close-up shots of things like flowers. This allows the camera to zero in on the subject in the middle and not be influenced too much by dark or light backgrounds.

Spot Metering
This mode is more selective than the centre weight, as it takes light information from only a small space. Some cameras let you choose which spot on the viewfinder you want the camera to focus on and some cameras let you choose how big an area that spot can be. Any light outside the area is ignored when calculating the exposure value in this mode. Some cameras let you change the spot area from the centre to other points in the frame. This is great for when the subject is small and the background lights are confusing like trying to take a picture of a person at night when there are lamps around them. Set the spot to the person and the camera will ignore the lights around the person.

Matrix Metering
Also called multi-spot or multipoint metering, this is generally the default mode where it takes light information from all points in the frame. It then uses certain algorithms to decide which points are most important and calculates the exposure. This is where the camera can make educated guesses such as when the top half the picture is brighter then the bottom. Cameras will often set more weight for the bright areas as it's easier to retrieve data from underexposed scenes then it is for overblown highlights. This is the default mode and basically used in any situation where you don't require the other two modes. Whether its landscape or portrait, assuming there isn't anything in the frame that is distracting like background lights or a candle on the side, this mode will do the job well.

While choosing the wrong metering mode won't entirely destroy your photos, they can come out a little weird with faces that are blacked out and highlights that are overblown, so as with most of your camera's functions, it's always a very good idea to become familiar with the metering modes as just another way to control exposure and to use them for the accordingly to various photo shooting situations.