| 摘要 |
PURPOSE:To read information with even a lens with low-capability, by using a magnetic field generating means to drive a projection lens with high efficiency in the vertical direction and the information track direction. CONSTITUTION:If a light spot is deviated from the information track in the vertical direction, the intensity of the light transmitted through a disc 1 is unbalanced between the left and the right of the center of the information track, and it is detected by a two-quadrant detector 8 connected to a potodetector 7, and the output is supplied to a coil 103 through a lead wire 106 to allow a force in the direction of an arrow A to act, and a projection lens 101 is moved in the direction of the arrow A, namely, in the direction vertical to an information track T. When the reduction magnification of the projection lens is denoted as M, the deviation of the light spot from the optical axis is the extent of movement of the lens, namely, M times as large as the accentric quantity of the information track; and M is reduced to zero when a parallel luminous flux is condensed, so that the projection lens has no aberration only for one point on the optical axis is sufficient. |
