Prism periscope

Claim 1

A periscope for observing an object comprising prism means adapted to pass light beams within the confines of two limiting light rays which define an acceptance angle for said periscope having a generally horizontal median and to prevent reflection of light back to said object, said prism means including an elongated body of transparent material defined by a plurality of contiguous, angularly related surfaces relatively arranged to define said acceptance angle and of a size not substantially greater than that necessary to accommodate rays within said acceptance angle, said surfaces including generally parallel side wall surfaces, a planar entry surface adjacent one end of said body for passing light incident thereon into said prism. Two substantially parallel internally reflecting surfaces positioned to transmit light within said prism means from said entry surface to said exit surface, said reflecting surfaces being inclined so that light incident on said entry surface within said acceptance angle makes an angle other than a right angle with said reflecting surfaces, said exit surface being inclined with respect to said reflecting surfaces so that beams of light incident on said exit surface and derived from light incident on said entry surface within said acceptance angle after reflection by said reflection surfaces make an angle other than a right angle with said exit surface, and a plurality of light absorbing surface means on said side wall surfaces extending between said entry, exit and reflecting surfaces, said absorbing surface means being angularly arranged relative to said entry, exit and reflecting surfaces to prevent light reflected therefrom from emerging from said entry surface in a direction which lies along or above the horizontal and to receive light rays therefrom outside the angle of acceptance, and a protective casing means for supporting said prism means with said entry surface of said body fully exposed over a major portion of the working range thereof and inclined forwardly to the vertical at its upper edge at an acute angle within the range of from 10* to 40* to form an angle other than a right angle between the entry surface and the median of said acceptance angle.