Patent ID: 8465218

Claim:
An aperture unit used in an optical path of an optical system and configured to change a size of an aperture so as to adjust an amount of light passing through the optical system, the aperture unit comprising: a plurality of diaphragm blades linearly movable in a first direction perpendicular to an optical axis; and at least one diaphragm blade linearly movable in a second direction opposite to the first direction, wherein two of the plurality of blades that move in the first direction, one moves a larger distance at a high speed in the first direction than the other, wherein the two of the plurality of blades have shapes of apertures edges different from each other and the two aperture edges have parts parallel to each other which form a part of the aperture while a size of the aperture is changing, and wherein, there is a section where a predetermined polygonal aperture with more than four angles is formed by the aperture edges of the plurality of diaphragm blades that linearly move in the first direction and the aperture edge of the at least one diaphragm blade that linearly moves in the second direction during a part of a time period when the plurality of diaphragm blades that linearly move in the first direction and the at least one diaphragm blade that linearly moves in the second direction move so that the size of the aperture is decreased from an open aperture state, and there is a section where the predetermined polygonal aperture is formed by the aperture edge of the one of the two diaphragm blades among the plurality of diaphragm blades and one of the aperture edges of the at least one diaphragm blade that linearly moves in the second direction during a part of a time period when the plurality of diaphragm blades that linearly move in the first direction and the at least one diaphragm blade that linearly moves in the second direction move so that the size of the aperture is further decreased.