| 摘要 |
PURPOSE:To obtain an out-of-focus detecting system capable of self-adjusting the target of focusing by finding the modulation degree of two input signals modulated with a mark and making this difference signal an out-of focus detecting signal. CONSTITUTION:Reflected beams 10b, 10c by an optical disk 8 are attained to photodetecting elements 11b, 11c, by the elements 11b, 11c, light quantity signals 12b, 12c are outputted. When the disk 8 is moved to the horizontal direction of the paper face, the beams 10b, 10c are modulated by the mark of a pit, etc. The amplitude of the modulation of the signals 12b, 12c are outputted as a modulation degree signals 14b, 14c by that the upper level and the lower level of the amplitude of an inputted signal are detected and the upper level is divided by the lower level in an envelope detecting circuit 13b, 13c. A differential arithmetic circuit 15 is inputted with the signals 14b, 14c, and the difference signal is outputted as the out-of-focus detecting signal 16. Thus, the out-of-focus detecting system generating no offset to the out-of-focus detecting signal even when a part of a luminous flux is erased and capable of self-adjusting the target of focusing. |
