| 摘要 |
PURPOSE:To reduce an out-of-focus generated due to influence of an eclipse of an objective lens even when a distance between an optical disk and the lens is varied. CONSTITUTION:Focusing is regulated by a floated travelling function of a floating slider 5 for placing an objective lens 4 of a moving unit 1 of an optical system separately having the unit 1 and a fixed unit 2 and a driving function of a relay lens 9 of the unit 2 based on a focus error signal detected by a Foucault method. A shielding plate 13 having an opening 20 for transmitting only a light of a luminous flux center part by shielding a light of the outer peripheral side of the flux of a reflected light is installed between a beam splitter 10 of the unit 2 and a photoreceiver 17 of a detecting optical system 12. Even if the distance between an optical disk 3 and the lens 4 is varied, a luminous flux diameter of an incident light on the photoreceiver 17 and hence a light quantity becomes constant by partial shielding operation of the reflected light by the plate 13, an out-of-focus can be reduced. |
