Patent ID: 8657510

Claim:
An aperture stop mechanism comprising: a base plate having a fixed aperture hole; two aperture blades operative to be arranged so as to overlap each other and form a single light passage opening, into which light utilized in imaging is introduced, with the respective edge portions of the two aperture blades; and a drive mechanism operative to drive the two aperture blades in directions different from each other and thereby change an aperture area of the light passage opening while light-shielding the fixed aperture hole, wherein the two aperture blades are provided so as to form the single light passage opening, surrounded by boundaries including n (n=6, 8, 10) straight lines, with the respective edge portions of the two aperture blades, release light shielding of the fixed aperture hole so that the fixed aperture hole is opened at a predetermined maximum aperture position, form the light passage opening having an n-polygonal flat-shape at a predetermined minimum aperture position, form the light passage opening of a regular n-polygon at a predetermined proximate position between the maximum aperture position and the minimum aperture position, and form, from the maximum aperture position to a predetermined halfway position toward the predetermined proximate position, the light passage opening in which a part of the fixed aperture hole and the edge portions are combined.