Method for revealing optically distorting flaws in transparent sheet

摘要

A method of revealing the presence of flaws causing optical distortion in transparent sheet materials (1) of glass or plastic employs a focused (3) light beam projected at right angles to the sheet surface to impinge on a translucent viewing screen (2). Several alternative arrangements are suggested including an overhead projector, at metal-vapour point source lamp with or without a parabolic reflector and suitable beak control components (3). A video camera (6) is mounted behind the screen (2) and the various types of manufacturing flaw are observable as characteristically different images appearing on the screen (2).