Metering Systems

Most modern cameras include sophisticated meters for measuring the amount of light reflected from the area being focused on. This is how these cameras are able to automatically expose a scene under most circumstances: it calculates both the shutter speed and aperture (f number) based on readings from the meters.

The default is to use matrix (or honey comb) metering where measurements are taken from the entire area being focused using a regular pattern. The average of all such measurements is then used to calculate the correct exposure. This works well in a large number of cases.

If the scene has parts which are very brightly lit while others are in the shadow, the end result may be good but not what you expect. Perhaps what is in the shadows cannot be seen at all (under exposed) or, the brighter areas are far too bright and washed out (over exposed).

One possible solution to this problem is to use spot metering. In this case, a much smaller area in the centre is used to take measurements. You would then focus the part of the scene you want sharp and clear, lock the focus, move the camera until you achieve your perfect frame and...release the shutter. You are now able to bring details out of the shadows or, conversely get a clear and sharp view of that intensely iluminated part of your scene.

A third metering system known as center-weighted gives more importance to the measurements taken from the lower two thirds of the scene. This is intended to be used for landscape photography where the top third is dominated by a bright sky. A similar effect can be obtained with matrix metering and a gradient filter (but this should be the topic of a separate article).

On my camera, I can select the metering system from the menu options under Photometry.

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