Abstract: Prior to actual reproduction of an optical disk, test reproduction is performed with respect to a plurality of testing radial locations of the optical disk. In the test reproduction, waveform-equalization-characteristic parameters of the waveform equalization section are adjusted to optimal settings so as to optimize jitter of a reproduced RF signal detected at each of the testing radial locations of the optical disk. In the actual reproduction of the optical disk, the waveform-equalization-characteristic parameters of the waveform equalization section are adjusted to optimal settings that are predicted, from the optimal settings determined by the test reproduction, in accordance with a radial position or address, on the optical disk, of each location to be reproduced.

Abstract: A zoom lens includes a first lens group (1) having a positive refracting force that is fixed, a second lens group (2) having a negative refracting force that is movable along an optical axis and provided with a function of varying magnification, a third lens group (3) having a positive refracting force that is fixed, and a fourth lens group (4) having a positive refracting force that is movable along an optical axis and provided with a function of correcting fluctuations of an image plane resulting from varying magnification or changing an object distance (4), the first, second, third and fourth lens groups being disposed from an object side in this order, wherein the third lens group (3) and the fourth lens group (4) both include a positive glass spherical lens (L5, L8) and a plastic aspherical lens (L6, L7) having weaker refracting power. Thus, a compact zoom lens having a high magnification ratio of 20 times can be obtained at low cost.

Abstract: A zoom lens includes a first lens group (1) having a positive refracting force that is fixed, a second lens group (2) having a negative refracting force that is movable along an optical axis and provided with a function of varying magnification, a third lens group (3) having a positive refracting force that is fixed, and a fourth lens group (4) having a positive refracting force that is movable along an optical axis and provided with a function of correcting fluctuations of an image plane resulting from varying magnification or changing an object distance (4), the first, second, third and fourth lens groups being disposed from an object side in this order, wherein the third lens group (3) and the fourth lens group (4) both include a positive glass spherical lens (L5, L8) and a plastic aspherical lens (L6, L7) having weaker refracting power. Thus, a compact zoom lens having a high magnification ratio of 20 times can be obtained at low cost.

Abstract: Optical pickup is provided which includes a first reproduction channel for reproducing a first-type optical disk and a second reproduction channel for reproducing a second-type optical disk. When reproduction is to be performed on a third-type optical disk that is different from the first-type and second-type optical disks but reproducible via each of the first and second reproduction channels, the third-type optical disk is first test-reproduced both via the first reproduction channel and via the second reproduction channel, to thereby detect a jitter value of the information reproduced via the first reproduction channel and a jitter value of the information reproduced via the second reproduction channel. Then, the recorded information of the third-type optical disk is reproduced using one of the first and second reproduction channels that attains the jitter value closer to a predetermined target jitter value.

Abstract: A tilt control device for an optical disk device including a tilt error detecting section for detecting a tilt in radial tilt direction between direction of optical axis of an optical pickup at a point where the optical axis crosses an optical disk recording surface and direction perpendicular to the recording surface, a tilt actuator for driving the optical axis, a first tilt control circuit for driving the tilt actuator in accordance with a detected tilt error to correct the tilt error, a section for detecting a tilt amount from a reference position in the radial tilt direction of the tilt actuator, a section for detecting a position of the optical pickup in the radial direction of the disk, a storage section for prestoring tilt amount characteristics necessary for correcting tilt errors at respective positions in the radial direction of the disk, a second tilt control circuit for driving the tilt actuator in accordance with detection by the tilt amount detecting section for realizing a corresponding tilt a