| 摘要 |
PROBLEM TO BE SOLVED: To provide a method for controlling an objective lens with little out of focus even in the case of accessing an optical recording medium having a plurality of recording layers. SOLUTION: An out of focus is detected by a characteristic value other than the focus error signal, such as the amplitude of a push-pull signal amplitude for a tracking error signal for example, utilizing the nature that the maximum amplitudes of both an RF signal and the tracking error signal are obtained when the recording surface spots of the optical information recording medium having the plurality of recording layers are optimum, and that the recording surface spots are blurred with a defocusing and the amplitudes of both the RF signal and the tracking error signal are decreased. The defocusing due to an interlayer crosstalk or an error of the layer distance can be reduced in the case of accessing the medium having the plurality of recording layer, by correcting the defocus deviation by superposing an offset amount, on the basis of the detection result.
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