Diaphram

The diaphragm is the mechanism that controls the amount of light going into the aperture, or the center of the lense. It is meant to block all other light coming into the lense. That is why at points the diaphragm is sometimes known as a stop or aperture stop. The two types of diaphragms consist of the traditional, or rather older diaphragm and the iris diaphragm. Compared to the iris, the traditional diaphragms consist of a serious of blades that create the stop for the aperture; the larger amount of blades, the blurrier the end result.

-Wisco