Patent ID: 7878721

Claim:
A light amount adjuster for adjusting a size of a diaphragm aperture on an optical axis of an optical system, the light amount adjuster comprising: a pair of straight moving diaphragm blades so provided at a portion to which the diaphragm aperture is opposed as to slide along a plane orthogonal to the optical axis in a direction of getting close to or separated from the optical axis; a pair of swing diaphragm blades so provided at a portion to which the diaphragm aperture is opposed as to swing about a center axis in parallel to the optical axis in a direction of getting close to or separated from the optical axis; and a drive mechanism for adjusting the size of the diaphragm aperture by sliding the pair of straight moving diaphragm blades and by allowing the pair of swing diaphragm blades to swing, wherein there is provided a plurality of the pairs of swing diaphragm blades, one of the swing diaphragm blades of each pair of swing diaphragm blades of the plurality of pairs is provided on one face of the two faces to which the pair of straight moving diaphragm blades are opposed in the optical axis direction, and the other one of the swing diaphragm blades of each pair of swing diaphragm blades of the plurality of pairs is provided on the other face of the two faces to which the pair of straight moving diaphragm blades are opposed in the optical axis direction.