| 摘要 |
PROBLEM TO BE SOLVED: To make it possible to converge plural luminous fluxes to the prescribed positions of recording media by using one condenser lens and to reproduce the recording media varying in recording densities by specifying the ratio of the distance B between a second light source and a condenser leans to the distance A between a first light source and the condenser lens to a specific value. SOLUTION: The condenser lens 17 converges the luminous flux 2b from the light source 2 as the luminous flux 2d to the high-density optical disk 18 and converges the luminous flux 9b from the light source 9 as the luminous flux 9d to the low-density optical disk 19. The reflected light of the disk 18 is received by a photodetector 3 and the reflected light of the disk 19 is received by a photodetector 10. The ratio (L2/L1=H) of the distance L2 between the light source 9 and the condenser lens 17 to the distance L1 between the light source 2 and the condenser lens 17 is specified to 0.55<H<0.75. The wave front aberration amount existing in the incident light on the condenser lens 17 is thereby confined within a permissible range with respect to the light from the light sources 2 and 9. As a result, the reproduction of the low- density optical disk 19 by using the condenser lens designed for the high-density optical disk 18 is made possible. |
