Optical range finder with variableangle exponential prism

Claim 1

AN OPTICAL RANGE FINDER FOR DETERMINING DISTANCE TO AN OBSERVED OBJECT HAVING A KNOWN DIMENSION AND ADAPTED TO BE HELD TO THE EYE OF A VIEWER, THE RANGE FINDER COMPRISING (A) A PRISM HAVING AN ANGLE BETWEEN ITS FACES THAT VARIES AS AN EXPONENTIAL FUNCTION OF DISTANCE ALONG AN EDGE OF THE PRISM, SUCH ANGLE BEING ORIENTED SUBSTANTIALLY PERPENDICULAR TO SUCH EDGE, (B) A SIGHT OF LIMITED OPENING ARRANGED IN ALIGNMENT WITH SUCH EDGE FOR VIEWING THE OBSERVED OBJECT THROUGH A PORTION OF SAID PRISM AND SIMULTANEOUSLY VIEWING THE SAME OBJECT WITHOUT THE INTERVENTION OF SAID PRISM, THE SIGHT BEING MOVABLE WITH RESPECT TO THE PRISM ALONG A DIRECTION IN WHICH THE ANGLE OF THE PRISM VARIES, (C) A PAIR OF COOPERATING LOGARITHMIC SCALES, MOVABLE WITH RESPECT TO EACH OTHER, RELATING DISTANCE TO THE KNOWN DIMENSION OF THE OBSERVED OBJECT, IN ACCORDANCE WITH A RATIO THAT VARIES WITH THE POSITION OF ONE SCALE RELATIVE TO THE OTHER, AND (D) MEANS CONNECTING ONE SCALE TO SAID PRISM AND ONE SCALE TO SAID SIGHT FOR RELATIVE SCALE MOVEMENT WITH THE MOVEMENT OF SAID SIGHT RELATIVE TO SAID PRISM.