You may find three or four choices of metering mode on your camera. I will cover the four possibilities in this post. The meter selection mode can be found somewhere within the menu function on your camera or via a separate dial on the main camera body. Within the menu function it will look something like this:
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The modes, reading from left to right, are evaluative (as selected in the picture), partial, spot and center-weighted.
Evaluative - this is usually the default metering mode on DSLR cameras. The evaluative metering mode will take an exposure reading across the entire frame of the photograph which you are composing. The exposure will average out the light and dark across the picture and will bias the exposure towards the autofocus point on which you have focused the shot. This mode will usually offer a good exposure across the photograph and will suit many situations. Evaluative mode (Canon) may be referred to by different terms on different models, for example, it is referred to as Matrix Metering on Nikon cameras.
Partial - the partial metering mode will take an average exposure across a smaller area than evaluative. Again, the mode works out the average exposure around the focal point of the picture but in this case, it extends to around 8% of the area around the focal point rather than using 100% (i.e. the full picture).
Spot - this metering mode again works out the exposure around the point of focus in the picture. However, as for partial metering, the average exposure is then calculated on a much smaller proportion of the actual picture. In the case of spot metering around 2.4% of the picture area is used for the exposure.
You might wonder when you would use spot metering as it only works on such a small percentage of the picture. Because the mode uses just a very small area to set the exposure, it can be useful when you want a really accurate exposure to make something in the picture stand out, especially when there are big differences in light across your shot. For example, shooting someone against a bright window or a dark background. Using evaluative metering will average out the exposure and you will lose definition in the features. Using spot metering and focusing on the person's face will average out the exposure around the face and bring out features which would otherwise be lost.
When you select the area of the photograph which you would like to use for the exposure reading, you will need to lock the exposure here. If you don't do this, the exposure point will re-set when you move the lens to compose the final picture. Locking the exposure in on a Canon is simply a press of the star button (you should see a star icon in the viewfinder after pressing this button). On a Nikon, it is an AE-L button.
Center-Weighted Average (US spelling) - this mode works in a very similar way to evaluative metering but, as the name suggests, the exposure reading is averaged around the centre point of the picture which of course may, or may not, be where you have focused the picture.
I am still getting used to the metering modes and tend to shoot most of my pictures in the evaluative mode. However, understanding the difference between modes is a useful part of digital photography and will come in useful during anyone's photography journey.
That's all for now and as always, enjoy your photography.
