An optical comparator is an essential device required for constituting an optical communication system, or an optical measuring System wherein various instruments, apparatuses, equipments or optical circuit components are connected to each other via optical fibers. An optical comparator compares an optical signal with an optical threshold and indicates whether the threshold has been exceeded. Optical comparators incorporate a set of lenses which magnify an object placed in the field of view. The magnified image appears on a screen where it can be compared with templates or measured directly from the screen. Optical comparators impinge a beam of Light on a component part to be inspected. The shadow being brought into coincidence with an outline of a master or reference part engraved or otherwise formed on the screen.