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Unless you set your camera to manual mode, it will need to work out how much light is required to make the perfect exposure. To do this it must make a decision based on the bright, middle and dark tones in the image. The area in which the camera looks is dependant on the metering mode you choose. This article will discuss each of the modes and help you decide which one to use in various lighting conditions.
The Metering Modes
Each camera manufacturer may differ slightly in what it calls each mode, and how you select them, but there are generally three different ways (four if you shoot Canon) in which your camera will calculate the 'perfect' exposure:
This metering mode has a myriad of names depending on which camera brand you use. Its generic term is Multi-segment Metering, but is known by Matrix Metering (Nikon), Evaluative Metering (Canon), ESP (Olympus), Classic (Leica), Multi-pattern (Pentax)... the list goes on.
Multi-segment metering is the 'standard' metering mode that most people will use most of the time. In this mode, the camera breaks down the scene into different zones (segments) and evaluates each one for what it thinks is the correct exposure. It will then decide on an overall exposure value based on the zone values. The algorithms used are quite complex (and very secret), but priority will usually be given to the zone(s) that are in focus.
This metering mode works best when the scene has a relatively even distribution of tones and the subject lighting doesn't differ significantly from surrounding areas. Most cameras do a pretty good job in this mode and combined with a little exposure compensation (explained below) will often be the best choice.
In centre-weighted metering mode your camera will consider the entire scene, but put much more emphasis the centre of the frame. This mode doesn't consider where your focus point is like multi-segment metering does.
This metering mode works well when the subject is large in the centre of the frame and the exposure at the edges of the scene are less important than the subject. Portraiture is a good example of this.
Finally (except for Canon), spot metering works in a similar way to centre-weighted metering, but only looks at a very small area around your selected focus point. If you are focused on the eye of an animal the camera will evaluate the eye and surrounding area to make a decision about the exposure.
This mode should be used when your subject has a significantly different brightness to the rest of the scene. The camera will expose correctly for your subject and if the background differs by a great deal it will be under or over exposed.
A good example of this is when taking photos of the moon at night. The moon is quite small in the frame and very bright compared to the dark sky around it. In Matrix metering mode the camera will evaluate the scene to be overall quite dark, and the moon will be overexposed. Changing to spot metering will expose correctly for the moon and underexpose the sky.
Partial metering is an extra mode available on most Canon DSLR cameras. It works in a very similar way to spot metering but evaluates a larger area around the selected focus point.
Highlight Weighted Metering
In addition to the above, some camera manufactures also have an extra option added to all three of the above modes called 'Highlight Priority'.
When this option is selected it will meter as per your chosen mode, but will make sure that any bright areas in the scene are not over-exposed. This can be useful if you want to ensure that there are no 'blown out' bright areas in your photo that can't be recovered.
If the bright areas are much brighter than the overall scene this can lead to the image being underexposed. The highlight areas will be protected, but the darker areas will be underexposed as a result and will need to be pushed up in post-processing.
This feature works well when you want to make sure you don't overexpose the bright areas of an image, but the overall scene doesn't vary too much from the bright areas.
Overriding Your Camera
As good as modern metering systems are, they will never be perfect. If your camera has chosen an exposure that is too dark or too bright you can adjust it by dialling in some exposure compensation. This tells the camera to adjust the exposure up or down by whatever value you choose.
For example, if you are taking a photo of a primarily white scene, your camera might choose an exposure that is much darker than you'd like. In that case you would dial in some positive exposure compensation to tell the camera to brighten up the scene.
The method of applying exposure compensation will vary from camera to camera, so you may need to consult your manual. The compensation value is usually indicated somewhere in your camera's viewfinder so you can easily tell when and how much compensation has been applied. It is usually indicated by a +/- symbol.
How To Change Modes
Unfortunately this isn't an easy question to answer. Not only do different manufacturers have different ways to do this, often it will vary between camera models as well. Sometimes there will be a dedicated button on the body (Higher end Nikon Bodies), or a combination of buttons (Canon) or sometimes you will need to go into the menu settings.
It is certainly best to consult your camera manual to find out the exact method. You can also get in touch with us, or leave a comment below if you get stuck.
Your camera needs to decide on an exposure before you take a photo. How it does this depends on the metering mode you choose.
- Multi-segment Metering: Evaluates the entire scene to come up with an exposure that should work best in most situations
- Centre-weighted Metering: Evaluates the entire scene, but will prioritise what is in the middle of the photo to determine the exposure.
- Spot Metering: Looks at a small area around your chosen focus point to evaluate the correct exposure.
In most cases multi-segment metering will do a good job. When combined with manual exposure compensation for tricky scenes, this mode will probably suit most of your photography needs. When photographing scenes with extreme exposure differences between your subject and background you can switch to one of the alternatives.