All modern DSLR cameras have a selection of different metering modes. They all work to assist the photographer in obtaining the best exposure for the scene they are photographing. Understanding the difference between them and when to use them is essential to taking better photos.
What is Metering?
Essentially, metering is a method used by the camera to assess the amount of light in a scene. The camera then uses this information to adjust the shutter speed, aperture and/or ISO in order to correctly expose the photo.
The human eye is a very complex and versatile lens. When presented with a scene of varying levels of light, your eye can adjust itself to expose very accurately for all of them. Let’s say, for example, you are standing in front of a friend who has the sun directly behind them. Your eye can simultaneously adjust for the direct sunlight while also correctly exposing their face, even though it is in shadow.
In comparison, a DSLR camera can only adjust exposure for an entire scene as a whole. Therefore, the user needs to tell the camera how to meter the scene. Do you want it to expose for the direct sunlight, or expose for the face, or perhaps you want to expose somewhere in the middle of the two extremes? How about manually selecting a point in the frame to correctly expose for?
Which exposure variable your camera adjusts (aperture, shutter speed or ISO) will depend on which shooting mode you are in. If, for example, you’re shooting in Aperture Priority mode with your ISO set to Auto, your camera may adjust both your shutter speed and ISO in order to obtain a correct exposure. Set your ISO to a particular value and only your shutter speed will be adjusted. In addition to this, if you’re shooting in full Manual mode (where you’ve set the shutter speed, aperture and ISO yourself), the metering mode you set will no longer affect the final exposure of your shot since there are no exposure variables left for the camera to adjust. However, when in full Manual mode, your camera’s visual exposure meter will still adjust to show you the exposure of your shot based on the manual exposure settings you’ve dialled in and the metering mode you’ve set.
It can be tricky and no matter how advanced a photographer you are, there are still times when ‘trial and error’ plays its part. Arm yourself with an understanding of your camera’s different metering modes, however, and you’ll be better prepared the next time you need to take control.
Multi-Zone Metering or Matrix / Evaluative Metering
Often the default setting on most DSLRs, this method works best on scenes which are fairly evenly lit. Your camera divides the frame in to zones and individually measures their exposure, adding bias to any zones which have active focus points. It then takes all this information and makes an educated calculation on the best overall exposure for the entire image. Some older DSLRs may have an ‘Average Metering’ mode, which works like a multi-zone system except no bias is given to any particular area of the metered area.
In this aviation shot, below, the camera metered for the whole frame but also added bias around the four active focus points. Because this scene was evenly lit, the ‘Evaluative Metering’ setting was the best option.
Like evaluative metering, centre-weighted metering measures light across the whole frame but adds approximately 60-80% bias towards the centre. This is a great option for when you want to give exposure preference to what is dominating your shot.
Using the example given earlier of a friend standing in front of you with the sun directly behind them, your aim is to expose their dark face while adding some control over the exposure of the bright background. Centre-weighted metering tells the camera to concentrate on exposing the face, but to also bear in mind the background exposure. (FYI – a better approach here would be to have your subject turn 90 degrees to the sun thus helping to eliminate bright sunlight and dark shadows from the shot).
In the image below, I used centre-weighted metering to prevent the model’s dark shirt and the dark carpet from overly affecting the overall exposure. I wanted the main metering bias to fall on the model’s face, while also giving consideration to the darker areas within the frame.
Partial Metering (Canon DSLRs)
Partial Metering (found on most Canon DSLRs) sets the camera to meter for approximately 6-8% of the viewfinder area around the active focus point(s). This option is useful when you have very bright or dark areas in the shot which you don’t want affecting the overall exposure of the image. (This area was fixed to just the very centre of the frame on older digital cameras).
Often the second most popular setting behind matrix / evaluative metering. On certain new cameras, spot metering takes a measurement at the active focus point – even if this focus point has been manually selected by the photographer. On other cameras, spot metering may only be active on the central focus point, so you need to check your user manual to identify which is true for the camera you’re using. With spot metering, only 1-3% of the frame is metered, so this method is very useful if you want to expose for one specific point. In practice, this setting is useful in studio portrait photography when shooting a model against a brightly-exposed, white background. Here you would spot meter on your subject’s face or eyes to ensure an accurate exposure, thus ignoring the background. Similarly with the opposite extreme such as concert photography, like in this shot below, when I didn’t want the dark background to affect the exposure of the highlight I was focusing on.
As with most settings on modern digital cameras, metering modes are there to help us photographers. Understanding them and knowing when and how to use them in the field will lead to you taking better photos and getting it right in-camera, first time – and that’s the goal of every photographer.
Author – Oliver Pohlmann
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