Focusing screen

Abstract

A focusing screen for use in the finder system of a camera such as a single-lens reflex camera, and a method of forming a microstructure array suitable for use in the production of such a focusing screen. The focusing screen includes an optical material in plate form having on one surface a plurality of small lens portions that project in a regular array of equilateral triangles from the optical material and each of which has concentric contour lines, with a central apex. A flat portion is formed between adjacent small lens portions and a constricted portion is formed in the middle portion of the inclined surface of each small lens portion, with an irregular pattern of finer asperities is formed on the surfaces of the small lens portions and the flat portion. The high and low spots can be reversed. The method of forming a microstructure array includes the steps of forming a fine pattern of elements on a layer of light-sensitive material capable of transforming a distribution of light intensity to a surface relief by exposing the layer through a microlens array to rays of light with an intensity distribution corresponding to individual elements of the fine pattern. The microlens array may be replaced with a group of pinholes.