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.
- Also called iris.
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How to use iris diaphragm in a sentence
Rack the condenser down slightly and cut down the aperture of the iris diaphragm so that the light, although even, is dim.The Elements of Bacteriological Technique | John William Henry Eyre
They are also fitted with indicator for registering each exposure as made and iris diaphragm.Kodaks and Kodak Supplies, 1914 | Canadian Kodak Company
The simplest way of achieving this is by means of what is called an iris diaphragm.
To illustrate the functions of the iris diaphragm we will take the Williamson instrument.
By the aid of the iris diaphragm the diameter of the aperture may be varied from approximately ⅗ to ⅛ of an inch.
British Dictionary definitions for iris diaphragm
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 aperture: Sometimes shortened to: iris
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