Patent GB-717822-A (GB)
Title: Improvements relating to optical range-finders
IPC: G01C3/12
Filed: 1950-05-15
Abstract: 717,822. Range-finders. BAUMGARTNER, W. J. Aug. 15, 1951 [May 15, 1950], No. 12090/50. Classes 97(1) and 98(1) A range-finder has a movable optical element which can be caused to move to set the instrument for various distances by actuating a driving member, and an optical element which is normally stationary but can be moved to zero the instrument, the movements of the driving member being transmitted to the movable optical element by an intermediate member, the path of movement of which may be altered to vary the velocity ratio between the driving member and the movable optical element, the arrangement being such that the position of the movable optical element when the range-finder is set at a particular distance, e.g., infinity, is independent of the velocity ratio. Instead of moving the normally stationary optical element for zeroing purposes. the movable optical element may be moved independently of operation of the driving member to fulfil the same purpose. The range-finder shown is of the horizontal split field type and includes prisms 6, 7 for receiv= ing light from windows 3, 4 and directing it into an eyepiece 5, the inner end of prism 7 resting on the corresponding end of prism 6. Masks 19, 20 defining the appropriate fields of view register with the windows 3, 4 and for displacing the image formed by light through window 4, an optical wedge comprising lenses 21, 22 is mounted in the light path from that window. These lenses are mounted on carriages 23, 24, pivoted about a pin 25. During assembly, carriage 23 is adjusted until lens 21 is correctly positioned and is thereafter held fast by a screw 26 passing through a slot in the range-finder casing. A spring 28 presses the carriage 24 onto a dimple 27 on carriage 23 and this carriage is held spaced from carriage 23 by levelling screws 30, 31 which subtend a right angle at the dimple. Initially, the screws 30, 31 are successively actuated so as to set lens 22 in its right position with the image formed by light passing through window 4 in its correct vertical position and not tilted. The range-finder is operated by a milled knob 32 carried by a sleeve 41, freely rotatable about a pin 42 and carrying a cam 43 which contacts a pin 44 on a lever 47, pivoted at 48 to a link 49. This link is pivoted at 50 and has a serrated free end 51 engageable by a spring stop 52. A coil spring 90 on pin 25 urges a projection 45 on carriage 24 into constant engagement with pin 44. During assembly, lever 49 is rotated about its axis 50 until the rate at which the image formed through window 4 moves across the field of view through eyepiece 5 is that required and then spring stop 52 is caused to engage with lever 49 and hold it fast. Knob 32 carries a range scale which may register with any one of three depth of focus scales carried on a rotatable card and these scales are viewable through a window in the top of the casing. In another embodiment the two prisms are mounted with their lower faces in the same plane and the adjacent end surfaces thereof are cemented together over a small central spot, and the lens carriage 24 is in two interconnected parts one of which has a projecting area engaging a shoulder on a member mounted on the camera front and following a cam provided on the lens focusing ring. This member can be rocked to alter the effective length of the projecting arm and hence the rate at which the image seen in the central spot moves as the cam is rotated. Specification 633,510 is referred to.