Metering and Exposure

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Introduction To Metering and Exposure

A camera’s metering mode generally refers to the way the camera itself decides which is the correct exposure for a picture. A cameras metering system is the brains behind how your camera determines the shutter speed and aperture, based on lighting conditions and ISO speed; in-camera metering is standardized based on the luminance of light which would be reflected from an object appearing as middle gray.
Today, digital cameras users have the ability to choose and adjust the wide range of metering mode, or how the camera measures the brightness of the subject. Understanding these can improve one’s photographic intuition for how a camera measures light.
Here is a brief introduction to the most common metering modes available.

Spot metering:

Spot metering takes a reading from a very small part of the image and ignores the exposure of the rest of the scene.
About 1 – 5% view finder area is measured.
The readings are usually taken from very centre of the scene.
This method of metering is very accurate.
Spot metering is usually used very high contrast scenes.
Center-weighted average metering:

Here a metering is taken from the whole of the scene first, then the central spot an average reading is then calculated.
60 to 80% view finder area measured.
It is usually possible to adjust the weight/balance of the central portion to the peripheral one.
Less influenced by small areas that vary greatly in brightness at the edges of the viewfinder, more consistent results can be obtained

Average metering:

Light information comes from the entire scene and is averaged for the final exposure setting.
No weighting to any particular portion of the metered area.

Partial metering:

This is most common in Canon cameras.
10-15% of the view finder area is measured.
Partial metering is used when very bright or very dark areas on the edges of the frame would otherwise influence the metering unduly
Partial metering is found mostly on Canon cameras.

Multi-zone metering:

A type of metering first introduced by the Nikon, zone is a type of metering which takes readings from several different areas – or zones – within the scene to produce a calculated average.
Also called Evaluative/Matrix (Nikon), Evaluative (Canon). This is the default/standard metering setting on a number of cameras.
Light intensity measures from several points in the scene, and then combined to find the settings for the best exposure.
The idea behind multi-zone metering is to reduce the need to use exposure compensation


Author:
Chas Demain

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