The present invention is directed to a lens diaphragm device that can avoid a
degradation of an image due to both diffraction of a light beam and flares. The
diaphragm device includes two diaphragm vanes (2 and 4) that respectively
have notches (28 and 36) opposed to each other in a single plane
perpendicular to an optical axis (O), and two of the vanes are moved close to and
apart from each other in the single plane so as to vary an aperture of the lens
diaphragm. The lens diaphragm device also includes two optical filters (6 and
8) used to reduce a quantity of a beam of light passing through the diaphragm,
and an aperture of the diaphragm defined by edges of the optical filters and the
notches of the vanes is shaped to be asymmetrical about straight line which crosses
the optical axis and is perpendicular to directions of the motion of the vanes.
