Oblique Interference Filter for Nonparallel Light

Narrow-band multilayer transmission filters for use in an oblique position have been made to exhibit substantially uniform peak transmittance for all rays in a strongly converging beam. The required increase of film thickness with distance from an asymmetrically placed axis can be produced by appropriate baffling. Residual errors of ±3 A are approximately equal to reported random variation in thickness of evaporated films. Filters of 13 layers designed for binocular visual use have shown transmittances above 70% over a field 10° square.