| 摘要 |
PROBLEM TO BE SOLVED: To decrease the variations in the focus offset set by calibration. SOLUTION: A first mode using an outer periphery test region is set (St1). The averages of the error rates of reproduction data of three sectors and four sectors within one round are respectively determined at the respective change values of the focus offset (S2 to ST5). The optimum focus offset is determined from the quadratic approximation curve of the focus offset and the error rates relating to the three sectors of one round and the optimum focus offset is determined from the quadratic approximation curve of the focus offset and the error rates relating to the four sectors of one round. These focus offsets are averaged by addition to determine the final focus offset (ST6 to ST8). A second mode to use the inner peripheral test region is thereafter set (ST9, ST10) and similarly the final focus offset is determined. The final focus offsets determined in the first and second modes are used to determine the focus offsets in the respective zones of the disk by linear interpolation, etc. These focus offsets are stored as set values into a memory (ST11, ST12).
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