iris diaphragm(n = noun.artifact) iris - diaphragm consisting of thin overlapping plates that can be adjusted to change the diameter of a central opening;
is a kind of diaphragm, stop

   An adjustable diaphragm, reminiscent of the iris of the eye in its action, 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. [Webster 1913 Suppl.]

apatura iris, bearded iris, beardless iris, bulbous iris, contraceptive diaphragm, dalmatian iris, dame jean iris murdoch, diaphragm, dutch iris, dwarf iris, english iris, florentine iris, genus iris, german iris, gladdon iris, iris, iris cristata, iris family, iris filifolia, iris florentina, iris foetidissima, iris germanica, iris germanica florentina, iris kaempferi, iris kochii, iris murdoch, iris pallida, iris persica, iris pseudacorus, iris scanning, iris tingitana, iris verna, iris versicolor, iris virginica, iris xiphioides, iris xiphium, japanese iris, persian iris, spanish iris, stinking iris, vernal iris, xiphium iris, yellow iris