ISO rating
noun
photog a classification of film speed in which a doubling of the ISO number represents a doubling in sensitivity; for example, ISO 400 film requires half the exposure of ISO 200 under the same conditions. The system uses identical numbers to the obsolete ASA rating
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Word Origin for ISO rating
C20: from I nternational S tandards O rganization
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
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