iris diaphragm

American  

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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iris diaphragm British  

noun

1. Sometimes shortened to: iris.  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

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Etymology

Origin of iris diaphragm

First recorded in 1885–90

Example Sentences

In the lower power objectives the angular aperture is to be reduced by the iris diaphragm.

From Project Gutenberg

They are also fitted with indicator for registering each exposure as made and iris diaphragm.

From Project Gutenberg

The shutter leaves are formed of segments opening in star shape, giving even illumination over the entire plate the instant the exposure is started, and it has an iris diaphragm.

From Project Gutenberg

Rack the condenser down slightly and cut down the aperture of the iris diaphragm so that the light, although even, is dim.

From Project Gutenberg

Tycho Brahe invented, and applied to the pointers of his instruments, an aperture-sight of variable area, like the iris diaphragm used now in photography.

From Project Gutenberg