GB529417A - Improvements in or connected with optical observation instruments - Google Patents

Abstract

529,417. Range-finders. BARR & STROUD, Ltd., and FRENCH, J. W. May 31, 1939, No. 15992. [Class 97 (i)] In conjunction with monocular or binocular telescopes, and like hand instruments not ordinarily adapted for range estimation, reflecting means directs into the field of view a beam reaching the instrument at a position outside the normal entrance pupil, and is adjustable so that the two resultant images of a distant object may be brought into set relative positions ; knowledge, or assumption, of a dimension of the object then enables the range of the object to be read from a scale indication. As shown, a prism E above the objective H of one limb A of prismatic binoculars reflects to a prism G reflecting into the field of view. The prism E is rotatable in a carrier D by an arm 4 pressed by a spring 8 into engagement with a rod 7 engaging an annular cam 6 rotatable about the objective axis by an operating head 9. A fixed scale 10 graduated in accordance with object dimensions is provided in a groove in the head 9, and the range is read from a scale on the head 9 ; for station keeping at sea, the head may also carry scales indicating the increase or decrease of distance necessary for the observer to keep station. The prisms &c. are carried by a mounting C of annular form fitting over the body of the limb A, and the carrier D &c. may be movable on the mounting to displace the prism G from the field of view.