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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

Word Origin for ISO rating

C20: from I nternational S tandards O rganization
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012