[1] : The Collaborative International Dictionary of English v.0.48

iris diaphragm \i"ris di"aphragm\
   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. +pjc

[2] : WordNet (r) 2.0

iris diaphragm
     n : diaphragm consisting of thin overlapping plates that can be
         adjusted to change the diameter of a central opening
         syn: iris
see also:
iris 

Iris Diaphragm >> I Words
Iris Diaphragm, definition of term: Iris Diaphragm
iris+diaphragm_pag1.html

Iris >> I Words
Iris, definition of term: Iris
iris_pag1.html

Diaphragm >> D Words
Diaphragm, definition of term: Diaphragm
diaphragm_pag1.html