Focus detection method involving cutting more than half of light beam reflected from disc

摘要

A knife edge type focus detection method for optics associated with an optical pickup is disclosed. A light intercepting member is interposed between an object lens and a light receiving element for focus detection in order to cut 60-95% of a reflected flux for focus detection before the flux reaches the light receiving element. The intercepted part of the flux includes a light ray which propagates through the optical axis of the optics.