Aperture setting device

A center aligning device comprising:

• a first aperture setting means comprising a first frame having a circular outer circumference and inner edges each forming a portion of one side of a polygon, at least three first movable pieces circularly arranged inside said first frame for slideable movement relative to one another and relative to the edges of said first frame in a common plane, each of said first movable pieces being approximately triangular in a plane parallel to said common plane and having an elongated hole formed therein, a portion of one side of each of said first movable pieces forming one side of a first polygonal aperture to be set, and a first drive member disposed opposite one side of the faces of said first movable pieces and having first drive pins thereon, each of said first drive pins being inserted into a corresponding one of said elongated holes of said first movable pieces for simultaneously moving said first movable pieces relative to said first frame to set the size of said first polygonal aperture;
• second aperture setting means for setting a second polygonal aperture, said second aperture setting means comprising a second frame, second movable pieces, and a second drive member arranged in the same manner as those of said first aperture setting means;
• and
• coupling means for coupling said first and second aperture setting means to one another such that the axis of said first polygonal aperture coincides with the axis of said second polygonal aperture and the movements of said first and second drive members are independent of each other.