| 摘要 |
PURPOSE:To improve the precision of focusing detection by setting a plane formed by rotating around an axis intersecting orthogonally with the optical axis of an optical means, which forms plural discrete optical images or a contin uous optical image on a straight line, so that this plane is not in parallel with the straight line or the optical axis. CONSTITUTION:A principal beam 3 of a luminous flux 1 from an information recording medium is made orthogonally incident on the axis of a cylindrical lens 2 and is received by light detecting faces 5A and 5B in a plane formed by rotating around an axis 7 and is formed to a bobbin shape 9 which is constricted at the intersection between a linear image 4 and the plane 8. The light quantity density is maximum at the middle between light receiving faces 5A and 5B in the focusing state, and the light quantity density is reduced according as going away from said intersection when the width of light receiving faces 5A and 5B is made narrower than that of the linear image 4 in this point, and the same quantity of light is made incident on light detecting faces 5A and 5B at the time of focusing, and the change of the quantity of light is photoelectrically converted to detect focusing. |
