| 摘要 |
PURPOSE:To omit the high positional accuracy and the delicate adjustment needed in a production process for a photoelectric converting means and to obtain a reader which is highly resistant to vibrations, by changing a space between a recording medium and an image forming optical system in response to the output results of 1st and 2nd photoelectric converting means that receive the reflected beams from different images formed on plural data trains of an optical recording medium. CONSTITUTION:Three beams (a)-(c) delivered from a laser oscillator 44 form images on a data recording line 32 and a tracking line 31 on an optical card 11 through a diffraction grating 45, a polarized beam splitter PBS46, a lambda/4 plate 47 and an image forming lens 48. Then the reflected beams (a)-(c) travel back and reflected again by the PBS46 to be made incident on the photodetectors 50, 52 and 51. The outputs of photodetectors 51a and 51b are supplied to a tracking servo circuit while the outputs of photodetectors 50 and 51 are supplied to a focusing servo circuit. Then the lens 48 is moved up and down for focusing in accordance with the difference of signals between both servo circuits. |
