| 摘要 |
In a focus detecting optical system wherein a beam transmitted through an objective optical system is divided to thereby effect focus detection, a beam reflected by an optical disk is transmitted through an objective lens and a half mirror and is condensed by a condensing lens. The light beam from this condensing lens is divided by a dividing member comprising a pair of obliquely disposed plane parallel plates and becomes divided beams parallel to each other, and these divided beams arrive at a four-division detector. The dividing lines of this detector are on the meridional plane of the objective optical system.
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