| 摘要 |
PURPOSE:To detect stably out-of-focus, and also to discriminate an off-position direction by constituting a photodetector by providing at least eight photodetecting parts consisting of four in side photodetecting parts and four outside photodetecting parts. CONSTITUTION:In case an objective lens has approached a disk from a just focus position, when it is separated enough from the just focus position, a signal Le+Lh is detected, and thereafter, a signal Lf+Lg is detected, and in case said lens has gone away, the signal Lf+Lg is detected first, and thereafter, the signal Le+Lh is detected. An out-of-focus detecting circuit 51 always monitors the signals Le+Lh, Lf+Lg which are inputted from an out-of focus detecting signal processing circuit 50, detects an off-position direction by an out-of-focus and which signal is detected first, when an output has appeared in one of them, and outputs the signal to a focusing driving circuit 41.
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