Apparatus for detecting optically defects

Abstract

An apparatus for detecting optically defects in object such as original glass disc for use in manufacturing video and audio discs by projecting a laser light flux onto the object includes an objective lens for focussing the incident laser light flux onto the object as a small light spot, the laser light flux passing through the objective lens at only its central portion. When the object has no defect in the light spot area, the laser light flux is regularly reflected by the object surface, but when the object includes a defect in the light spot area, the light flux is scattered by the defect. The directly reflected and scattered light fluxes are collected by the objective lens and are then separated from each other by means of a small mirror arranged in an optical axis of the directly reflected light flux. The directly reflected and scattered light fluxes thus separated are received by first and second light detectors. A cylindrical lens is inserted between the small mirror and the first light detector having four divided light receiving regions. The objective lens is driven into an in-focussed position under the control of a focussing error signal which is derived by processing output signals from the four divided light receiving regions. A defect signal is derived by processing output signals supplied from the first and second light detectors.