| 摘要 |
PURPOSE:To detect easily an in-focus time and prevent surely the erroneous confirmation of the in-focus time, by providing the third photodetecting cell for detecting the in-focus time between the first and the second photodetecting cells for detecting the out-of-focus state. CONSTITUTION:The reflected light from an information forming layer 4 is irradiated to a photodetector 26, and the quantity of light irradiated to the third photodetecting cell 26b is monitored by a comparator 32; and when this quantity exceeds a voltage sent from a standard voltage generator 33, it is reported to a CPU31 that it is the in-focus time, and a focus loop is operated. At the out- of-focus time, a difference is generated between quantities of light irradiated on the first and the second photodetecting cells 26a and 26c, and an object lens driving driver 35 is operated in accordance with this difference of the quantity of light, and an object lens 17 is moved in such direction that the out-of-focus state is dissolved. When the degree of the out-of-focus state is higher and the quantity of light irradiated to the third photodetecting cell 26b exceeds a certain value, this state is detected by the CPU31, and the operation of the focus loop is stopped. |
