A light-quantity adjusting apparatus which can temporarily suppress an MTF
(contrast) from being deteriorated by small-aperture diffraction is
disclosed. The light-quantity adjusting apparatus comprises a main body
in which an opening is formed, a light-blocking member moved with respect
to the opening to change an area of a light-passing aperture, an optical
filter moved with respect to the opening to insert and remove with
respect to a region opposed the light-passing aperture, an actuator
serving as a drive source, a drive mechanism for driving the
light-blocking member and the optical filter by drive force from the
actuator.