| 摘要 |
PURPOSE:To narrow down a light beam into a sufficiently small light beam spot and to improve the reproducing output of an information signal by providing an opening diaphragm part and shielding the peripheral part of an objective lens. CONSTITUTION:The light beam is condensed through an objective lens 29 onto the surface of an information recording medium and the out-of-focus and track groove deviation of the light beam spot are detected. Then, a current corresponding to the amount of the detection is supplied to a coil 34 for focusing control and a coil 35 for tracking control and a lens holder 31 is rotated or vertically moved. Afterwards, the lens 29 is followed up in a focus direction or a tracking direction. In such a case, on the lens 29 side of a light beam incident hole 39 in the holder 31, an opening diaphragm part 40 is provided to shield the peripheral part of the lens 29 and the light beam is narrowed down into the sufficiently small light beam spot so as not to be incident to a part near a flange 41 of the lens. |
