Interference film filter for copying machine

摘要

An interference film filter for use in a copying machine as mounted on an optical path of light traveling through an image-forming lens for preventing transmission of the light in a predetermined wavelength range. The filter comprises a transparent glass substrate, and interference films each consisting of a plurality of layers formed by vapor deposition on the substrate. The interference films include a film disposed centrally of the substrate, and an opposed pair or pairs side films. Each of the side films has a greater optical film thickness than the center film or a film disposed immediately inwardly.