Patent ID: 7625142

Claim:
A light quantity adjusting device comprising: a substrate that is substantially flat and comprises an optical path aperture, a blade mounted on a front surface of the substrate operable to adjust a quantity of light passing through the optical path aperture, and an electromagnetic driver mounted on a rear surface of the substrate to drivingly open and close the blade, the electromagnetic driver comprising a rotor shaft with a permanent magnet, the rotor shaft including a narrowing first shaft end at one end and a cylindrical second shaft end at the other end; an exciting coil that applies a rotating force to the rotor shaft; an arm coupled to the first shaft end, the arm being coupled to the blade to adjust a quantity of light passing through the optical path aperture; and a frame that rotatably bears the rotor shaft, the frame comprising a conical bearing recess that supports the first shaft end and a cylindrical bearing hole that supports the second shaft end, wherein the electromagnetic driver is mounted so that the first shaft end of the rotor shaft is located at a rear surface side of the substrate, the exciting coil is wound around the frame and is configured to apply a rotating force to the permanent magnet, the frame has a sleeve-like yoke of a soft magnetic substance fitted around an upper half thereof and a tube fitted around a lower half thereof, the yoke exerts a magnetic attractive force on the rotor shaft to urge the first shaft end toward the bearing recess, and a magnetic detecting element is supported between the tube and the frame to detect magnetism in the rotor shaft.