| 摘要 |
PURPOSE:To obtain an optical pickup which is easy in optical axis alignment in an optical system and excellent in mass productivity by providing a cylindrical lens whose generating line intersects the plane of incidence of a half mirror at right angles in the optical path of the light transmitted by the half mirror in such a way that the departure line of the cylindrical lens connecting the central axis with the principal point can be inclined in the opposite direction to the inclination of the normal line of the half mirror in the plane of incidence. CONSTITUTION:A cylindrical lens 8 whose generating line intersects the plane of incidence of a half mirror 1 at right angles is provided in the optical path of the light transmitted by the half mirror 1 in such a way that the departure line of the lens 8 connecting the central axis with the principal point can be inclined in the opposite direction to the inclination of the normal line of the half mirror 1 in the plane of incidence. Since the magnitude of the astigmatism determined by the curvature of the cylindrical lens 8 is overwhelmingly larger than the magnitude of the astigmatism produced by some other reasons, the range of focus error detection can principally be determined by the curvature of the lens 8. Therefore, an astigmatic optical system can be designed independently regardless of the value of coma aberration to be corrected. |
