| 摘要 |
PROBLEM TO BE SOLVED: To preform the recording/reproducing of disks whose thicknesses are different like disks of a standard thickness type (CD, HDCD) and a thin thickness type (SD). SOLUTION: This reproducing device irradiates a laser beam on signal recording surfaces 51a, 52a of optical disks 51, 52 via an objective lens 24 and also reproduces a signal by guiding the laser beam to be reflected on the signal recording surfaces 51a, 52a to a photodetector 40. At this time, the effective numerical aperture is controlled by throttling the effective numerical aperture of the objective lens 24 in accordance with the ticknesses of substrates by a polarizing filter 31 so that a laser spot is made to be focused on the signal recording surface of the optical disk or by changing over the laser spot so as to be transmitted without throttling the spot by the polarizing filter 31 with respect to plural kinds of the optical disks whose thicknesses of substrates are different. Moreover, focal distances are changed in the inner peripheral part and the outer peripheral part of the objective lens 24. |
