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ISO rating

noun
  1. 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 © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012