Definition: The light sensitivity of a film or equivalent digital sensor sensitivity. The larger the number the less light is needed to capture the image. This sensitivity is measured by a formula developed by the international Standard of Organization and is abbreviated as ISO. Occasionally film speed is still designated by ASA, which is an older measurement standard from the American National Standards Institute.
Common Film Speeds
64
100
200
400
800
1600
3200
Also Known As: ISO, ASA
Source : http://photography.about.com/
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