Automatic focussing device

摘要

An automatic focussing device which functions to bring a video disc surface in focus with an optical system is disclosed. The device comprises a hologram for producing a focussing luminous flux having astigmatism with or without coma and a video signal reading out luminous flux without having astigmatism with or without coma, a relay lens having an optimum image forming plane, and an objective lens arranged such that said optimum image forming plane and said video disc surface are conjugate with respect to said objective lens.