| 摘要 |
PURPOSE: To provide an optical system capable of focusing a luminous flux on two kinds of disks having different thicknesses by reducing aberration to the minimum and reproducing them by adding only a simple function to the signal optical system. CONSTITUTION: This system comprises a changeover means for changing a relative interval between the optical axis directions of a semiconductor laser 1 and the luminous flux of a collimator lens 7 so that the interval becomes at least two different distance. The system has a structure for focusing a luminous flux on the signal recording surfaces of at least two kinds of recording media 9, 14 having different thicknesses of protection layers with a smaller aberration. |
