Metering mode
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In photography, the metering mode refers to the way in which a camera determines the correct exposure.
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[edit] Examples of Metering Modes
Cameras generally allow the user to select between spot, center-weighted average, or matrix metering modes.
[edit] Spot Metering
With spot metering, the camera will only measure a very small area of the scene (between 2-5% of the viewfinder area). This will typically be the very centre of the scene, but some cameras allow the user to select a different off-center spot, or to recompose by moving the camera after metering. Some cameras (including the Olympus OM-4 and Canon T90) support a Multi-Spot mode which allows multiple spot meter readings to be taken of a scene that are averaged. Both of those cameras and others also support metering of highlight and shadow areas.
Spot metering is very accurate and is not influenced by other areas in the frame, one common use is in very high contrast scenes. For example, if your subject's back is being hit by the rising sun and the face is a lot darker than the bright halo around their back and hairline, this is called being backlit. Spot metering allows the photographer to measure the light bouncing off of the subject's face and expose properly for that, instead of the much brighter hairline and a dark face. The area around the subject's back and hairline will then become over-exposed. Spot metering is a method upon which the zone system depends.
[edit] Center-weighted average metering
In this system, the meter concentrates between 60 and 80 percent of the sensitivity towards the central part of the viewfinder. The balance is then "feathered" out towards the edges. 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.
[edit] Average Metering
In this metering mode the camera will use the light information coming from the entire scene and and averages for the final exposure setting, giving no weighting to any particular portion of the metered area.
[edit] Partial area metering
Some cameras support metering of just the central area of the frame. This mode meters a wider area than spot metering, and is generally used when very bright or very dark areas on the edges of the frame would otherwise influence the metering unduly.
[edit] Matrix metering
This mode is also called multi or evaluative; and honeycomb metering on some cameras. This metering mode was first introduced by the Nikon FA, where it was called Automatic Multi-Pattern metering. Here the camera measures the light intensity in several points in the scene (more expensive cameras generally measure in more points) and then combine the results to find the settings for the best exposure. How they are combined varies from camera to camera. Many cameras use focus distance from the lens (if that is available) or data from the autofocus system to help with this decision. More advanced cameras with many autofocus points will know what parts of the matrix of metering zones are in focus and thus likely to be part of the main subject. Such metering is sometimes called 3D Matrix Metering. The actual number of zones used varies wildly, from several to over a thousand. However performance should not be concluded on the number of zones alone, or the layout.
On a number of cameras this the default/standard metering setting. However, some photographers, including some advanced photographers and some older photographers who are accustomed to more traditional metering methods, may be uncomfortable with matrix metering, this tends to stem from a lack of clarity about "how" the camera reacts in certain situations.
Many manufacturers closely guard the exact calculations used to determine the exposure. In general a number of factors are taken into consideration, these include: Autofocus point, distance to subject, areas in focus or out of focus, colours and hues of the scene, and back lighting. Matrix tends to bias its exposure towards the autofocus point being used, thus ensuring that the point of interest has been exposed properly. A database of many thousands of exposures is often pre-stored in the camera, and the processor can use a selective pattern to determine what is being photographed. Some users have problems with wide angle shots in high contrast, due to the large area which can vary greatly in brightness, it is important to understand that even in this situation, the focus point can be critical to the overall exposure.
[edit] External links
- Metering in the Digital Photography Review glossary.
- Camera Metering & Exposure: discusses incident vs. reflected light, evaluative, partial and spot metering.
- Understanding Metering: A very basic explanation of various metering modes with example
