iris diaphragm

Etymology
Its action is reminiscent of the iris of the eye.

Noun

 * 1) An adjustable diaphragm by which the diameter of an approximately circular opening may be controlled, as for regulating the aperture of a lens; it consists of a number of movable thin curved plates fastened at regular intervals around the inside of a ring, the positions of which are simultaneously adjusted by a single knob on the outside of the lens. It is used in cameras and microscopes.

Translations

 * German: Irisblende
 * Tagalog: