| 摘要 |
PURPOSE:To attain the focusing with simple constitution by using the 2nd and 3rd photoelectric conversion means placed before and after the 1st photoelectric conversion means so as to output an electric signal in response to the sharpness before and after an image formed onto the 1st photoelectric conversion means and detecting a focal point from a difference signal of the outputs so as to move the 1st photoelectric conversion means to the focal position. CONSTITUTION:A reflecting light beams in response to the reflectance of each pit 11 of a recording sector 11a is obtained from an optical recording card 11 into which light beams are irradiated, the reflected light beams are magnified by an objective lens 23 and the result is made incident in a photo diode array 241 via a transparent member 25. The reflected light beams pass through parts 25a-25c of the transparent member 25, each optical path length is changed and the light is made incident in ranges B, C1 and C2 corresponding to the photo diode array 241. A signal in response to the emitting light beams whose optical path length is changed by the member 25 is outputted from the array 241 and a horizontal synchronizing signal is outputted from a control section. |
