Patent ID: 7649821

Claim:
An optical disk discriminating method to be used when information on an optical disk in which a plurality of information layers are laminated is reproduced by an optical disk apparatus comprising: a laser light source for emitting laser light beams to record or reproduce the information on the optical disk; a collimating lens for converting the laser light beams from divergent light beams to substantially parallel light ones; an objective lens for focusing the laser light beams as a light spot onto the optical disk; a spherical aberration correction circuit for correcting a spherical aberration on the light spot; a detector for detecting part of the light beams reflected by the optical disk; an information layer number detector for detecting a number of information layers of the optical disk based on the reflected part of the light beams; and a memory for storing the detected number of information layers of the optical disk, the method comprising the steps of; setting a first spherical aberration correction value in the spherical aberration correcting circuit, thereby performing a focus search to thereby obtain a number L 1 of layers; and setting a second spherical aberration correction value in the spherical aberration correcting circuit, thereby performing a focus search to thereby obtain a number L 2 of layers and determining the number of the information layers of the optical disk based on the numbers L 1 and L 2 .