Metering mode#Average metering
When metering is the most common form of exposure measurement ( entire scene ), in which the entire photographic image field is used for light.
The metering is used both for SLR cameras with viewfinder cameras with built-in light meter as well as manual exposure knives. Similarly, work with private Flashes sensor with integral measurement.
The light intensity is on the whole area under an assumption of a standard gray level that would reflect exactly 18 percent of the light falling thereon is measured. In practice, this method often results in its pure form, especially at high subject contrast to incorrect exposures, as for example overvalued in landscape images of the bright sky or portraits with very bright or very dark environment, the real motive is mispriced.
Since the image important motifs are often located in the center, center-weighted average metering has very early enforced in a more or less large area of the picture section in the middle is rated stronger than the image area between the center and the edges. This yields under most circumstances related to the object proper exposure.
Manufacturers of SLR cameras have developed several refinements to the center-weighted metering. For example, the different evaluation for the Olympus OM -2 is realized by a printed on front-curtain pattern. In this system detects a arranged in mirror box measuring cell after closing the lens iris reflected by the light curtain and thus controls the exposure time. Minolta used CLC measurement in the two measuring cells are arranged so that the measuring ranges overlap in the middle in the SRT and the XE-series. Many cameras do not use circular, but rather a trapezoid measuring surface, wherein the lower half of the screen in landscape mode is considered stronger than the upper.
These measures will improve the reliability in average designs, and are obtained in a large part of the photographs ordinary results. If unusual lighting conditions, however, some experience with the peculiarities of the particular camera model is necessary for the photographer to take corrective.
The main disadvantage of the integral measurement compared to the spot metering is that the zone measuring method according to Fred Archer is not as feasible without further ado, the determination of the contrast range of a subject is only very inadequately possible.
The counterpart of the integral measurement is the partial metering or spot metering with concentrated measurement to a very small defined area, excluding the picture environment. Modern microprocessor- controlled cameras also offer the matrix measurement method. Some camera models also allow switching between different measurement methods. For digital cameras, except for very simple models, the choice between the different measurement method is standard today.