Patent GB-605492-A (GB)
Title: Improvements in or relating to range finders
IPC: G01C3/14
Filed: 1945-12-20
Abstract: 605,492. Range-finders. KODAK, Ltd. Dec. 20, 1945, No. 34575. Convention date, June 23, 1943. [Class 97 (i)] In range-finders of the type having a comparison plane or planes in which object images are formed by the optical system of the finder and which also has adjustment marks, images of which are formed by part of or all the optical system, one or both comparison planes contains a reflector having at least two reflecting surfaces for receiving the mark image beam and for reflecting it back through the optical system so that each image beam traverses the system at least twice, thereby increasing the sensitivity of the adjustment indication. The invention may be applied to coincidence and stereoscopic range-finders. In the stereoscopic finder shown in Fig. 4 images are formed in comparison planes 52 by optical squares 50 and lenses 51 for observation by eyepieces 56, a light deviator 68 effecting stereo coincidence of the images with marks in the comparison field. The right-hand field carries an adjustment mark 66 illuminated by lamp 60, light from which passes through lens 51 and is reflected to the other comparison plane via reflector 50, prisms 63, 64 and reflector 50 and lens 51. There the beam strikes a porro prism 65 and is reflected back through the system to form an image adjacent the mark 66. Coincidence of image and mark indicates correct adjustment. Alternatively, each comparison field may have an illuminated mark and a reflector for returning the beam from the other. The central prism system 53 may be replaced by the crossed reflectors of a coincidence finder, the illuminated mark being carried in the single comparison plane thereof. Alternatively, the marks may be external to the finder and be projected into it by suitable prisms and the adjustment mark images viewed by an. external eyepiece or eyepieces. Various modifications of such systems are described. The coincidence finder shown in Fig. 8 comprises reflectors 120, 128 reflecting light from the object to form an image in comparison plane 124 by a symmetrical objective 122. The second object image is formed in plane 124 by semi-transparent reflector 121 which reflects light to a reflecting surface 123 in the centre of the objective whence it is reflected back through mirror 121, the two images being seen in the eyepiece 125. Also in the plane 124 is an adjustment mark illuminated by lamp 126, light from which is collimated by the objective and is reflected from mirror 128 to the bevelled edge 129 of mirror 120, whence it passes via a bevelled edge 130 to the lens reflecting surface 123 to be focused thereby on the roof reflecting surface 131 in the comparison plane whence the light once more traverses the system and returns to form a mark image in the plane 124. An alternative form in which single mirrors, one at each end of a base, reflect light from the object through a single objective is also described. In the system shown in Fig. 16, a rotatable disc 190 bearing a spiral coincidence line 192 is mounted in the comparison plane of a coincidence finder. A portion of the line is illuminated by lamp 191, light from which passes through the range-finder system of the type shown in Fig. 4 and falls on a triple reflector 194 whence it is reflected back through the system to form an image 195. The rangefinder is adjusted until the object images coincide and the disc 190 is then rotated until line 192 and image 195 coincide, when the range may be read on a scale 196 against an index 197. Specifications 605,488, 605,490 and 605,491 are referred to.