Photo tip - Metering modes

03rd January 2010
The metering mode selected on a digital camera decides how the camera’s exposure sensor will react when a photo is taken. Different metering modes measure the light in a scene in different ways. But first here’s some background before I explain the different modes…
When a camera takes a picture it tries to make everything in the scene an average brightness (18% grey to be precise). Therefore it makes the blacks a bit lighter and the whites a bit darker. This is basically because cameras sensors are not able to ‘see’ as wide a range of contrasts as the human eye so it has to stick to the middle of the range.

So when you have extreme contrasts of light your camera tends to reproduce the colours poorly. Sunsets are a great example because you’ll either end up with a nice sky and a landscape that’s too dark, or a nice landscape and a sky that’s too bright.

Using the right metering mode can help, although often you need to use one of the following techniques if the contrast is beyond your camera’s scope:

- Use filters
- Use HDR software that merges several exposures
- Use your creativity to work around the problem. To take the sunset example, you could silhouette a church or boat (or any other well defined shape) so that it’s black against the properly exposed sky. Or you could over expose a bride’s white dress to give her an ethereal look while the rest of the image is well exposed.

Don’t worry if you’re confused as I’ll explain the difference between the four main metering modes and how to choose between them to take better photos.

Matrix / Evaluative metering mode
The Matrix or Evaluative mode splits the scene into many segments and then averages the exposure across the whole image. It’s great in most situations because you don’t need to think about it, however it can be fooled by high contrast scenes, in which case one of the other modes is preferable.

Partial metering mode
This mode looks at the central 10% of the image and assesses the amount of light in that area and ignores the rest of the scene. This can be useful when you have a particularly bright or dark background and you don’t want the matrix or evaluative mode to be fooled by the large expanse of black or white.

Spot metering Mode
This metering mode can provide excellent results for high-contrast scenes because it assesses between 1 and 10 percent (depending on your camera) of the scene, giving you a pretty accurate reading for that small area. To use it you need to half press your shutter button and then press the star button (Also called the AE lock button, which stands for Auto Exposure) to meter the area you want to expose for. You can recompose your camera after doing this so you don’t always have to expose for the middle of the image. In fact you can use any of the sensors on your viewfinder to expose from.
This is a great mode to practise with as it provides very different results even if you meter from slightly varying areas of brightness. It can even be used in relatively low contrast scenes to give different results, so fiddle at will and enjoy the creativity it brings.

Center-weighted metering mode
In this mode, the meter concentrates between 60 to 80 percent of the sensitivity towards the central part of the viewfinder. The balance is then "feathered" out towards the edges and averaged. One advantage of this method is that it is less influenced by small areas that vary greatly in brightness at the edges of the viewfinder; as many subjects are in the central part of the frame, consistent results can be obtained. This is the least commonly used mode though as it’s a bit of a half way house.

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