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iris diaphragm

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noun Optics, Photography.
  1. a composite diaphragm with a central aperture readily adjustable for size, used to regulate the amount of light admitted to a lens or optical system.
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Origin of iris diaphragm

First recorded in 1885–90
Also called iris.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

British Dictionary definitions for iris diaphragm

iris diaphragm

noun
  1. an adjustable diaphragm that regulates the amount of light entering an optical instrument, esp a camera. It usually consists of a number of thin metal leaves arranged so that they open out into an approximately circular apertureSometimes shortened to: iris
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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