What does Metering mean in Photography?
When is metering used? Well, it's being used every time you take a photograph. Metering tells the camera the settings to use for aperture, shutter speed, and ISO speed before it captures a photograph. In the automatic modes, the camera takes the settings from the metering data and sets the exposure accordingly. In the semi-automatic modes or manual mode, it displays whether the exposure settings will give an underexposed or overexposed or a properly exposed photograph, as displayed in the exposure level indicator inside the viewfinder or the LCD screen.
There are different metering modes inside the camera, they are:
Multi zone metering
Center-weighted average metering
In multi zone metering, also called evaluative, matrix, honeycomb, or segment metering, the camera measure the light intensity in several points in the scene and based on it, finds the settings for the best exposure. It is the metering mode that is most likely to suit most of your photography, but it doesn't do well in certain challenging situations, like backlit scenes, and scenes with uneven light distribution.
In center-weighted average metering, the camera takes in all of the view but gives more weight, or emphasis, to the light level around the center of the image, tailing off to little response at the edge. So a bright light at the edge of the image will have no effect on the reading. This way, center-weighted metering mode produces consistent results. In spot metering, the camera measures the light from a small portion (typically 1-5% of the frame) at the centre of the scene to determine the best exposure settings.
Since it meters only a very small portion of the scene, it is highly accurate in properly exposing the scene to get the right exposure. It is commonly used to shoot very high contrast scenes, a person standing against the Sun, for example. Spot metering can be used to measure the light coming off the person's face to expose it properly, rather than getting a dark silhouette had multi-zone metering been used. In contrast with spot metering, partial metering meters the central 10-15% of the image. It's useful when there are very dark or bright areas at the edges of the frame.
If any of the metering modes produces consistently underexposed or overexposed photographs in certain situations, then one can use the feature of exposure compensation to compensate for the incorrect exposure. For example, when photographing in snow, around +1 exposure compensation will always be required whereas in a low key photograph, negative exposure compensation may be required.
Like with everything else in photography, experimenting with the different metering modes is the way to go when trying to learn them. In different lighting situations, the mode may need to be changed to see the effect it brings on the photograph. It's best to mount the camera on a tripod and use the different metering modes one after the other to photograph the same scene and see the change and learn from it.
Written by : Ritesh Saini, IIT Mumbai (India)
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Edited by: Rajesh Bihani ( Find me on Google+ )