GB1291066A - Rangefinder - Google Patents

Abstract

1291066 Optical rangefinder K VOCKENHUBER and R HAUSER 25 Nov 1969 [25 Nov 1968] 57524/69 Heading H4D A rangefinder comprises a pulsed generator providing a collimated beam of radiation which is reflected from an object and imaged on to radiation sensitive detectors which determine the object range from the lateral displacement of the image and provide data relating to the range. An arc discharge lamp 29, Fig. 1, produces a flash of light when the switch 32 is depressed. An image of the arc is focused by lens 33 on to an object 28. The image on the object 28 is focused by lens 34 on to receiver 36, where several photo-diodes 35 are arranged, offset, from the axis. The light from the object falls on one of the photo-diodes, the range determining the particular photo-diode. The arc-discharge lamp 29 may be replaced by a GaAs diode emitting infra-red radiation or by a ruby or CO 2 laser. The receiver 36 detects the particular photo-diode being illuminated by monitoring changes in the radiation falling on all the photo-diodes 35. In the apparatus shown in Fig. 5, the signal from each photo-diode is amplified and fed through a differentiating capacitor 47 to the trigger input of a bi-stable circuit formed from transistors 54, 55. Thus any significant change in illumination of one diode causes one of the bi-stables to change its output state. The outputs of the bi-stables are connected through diodes 56 to the taps of a multitap resistor which forms one arm of a Wheatstone bridge circuit. The bi-stable which changes state causes all the resistors above it in the chain to be shorted out, thus the value of the resistance in that arm of the bridge determines the range of the object. In another embodiment the bi-stables drive lamps which indicate the range (Fig. 4, not shown). The voltage across the diagonal of the bridge may be measured directly by a meter calibrated in distance, or a differential amplifier formed from two transistors 60, 61 may be connected across the diagonal. The voltage difference is thus amplified and applied across a motor 50 which controls a variable resistor 59 in another arm of the bridge circuit. Thus the bridge is arranged to be balanced automatically. The capacitor 47, bi-stable and resistor chain may all be formed as an integrated circuit on a silicon chip, which may also carry the differential amplifier. The motor 50 is used to control the automatic focusing of a cine camera, Fig. 6. The transmitter 73 and receiver 78 are mounted on opposite sides of the optical axis of the camera lens system which comprises a variable magnification lens 63 and a focusing lens 64. The image of the object is focused through a semi-transparent mirror 66 on to the film through an exposure aperture 67. A rotating shutter 68 covers the aperture ,67 when the film is being advanced. Contacts 71 contacting a roller 70 provide signals which trigger the flash generator 74 to operate only while the film is covered by shutter 68. The motor 80 moves the lens 64 axially to focus the object and the position of the lens is represented in the bridge circuit by a variable resistor 81. In a further modification of a cine camera (Figs. 7, 8, not shown), a depth-of-field calculator (87) determines the range of focus using lens (82) and variable aperture (86). The calculator (87) drives a: rack (88) and two pinions (89, 90) which either obscure those photo-detectors which correspond to ranges outside the depth of field in which case an alarm may be provided to indicate that a flash has not been received or the pinions may carry photo-detectors which indicate directly when the object is outside the range of focus. In a modification (Fig. 9, not shown) the detectors are arranged on a plane (104) inclined to the axis of the receiver and passing through the point of intersection of the transmitter axis and that axis of the lens (103) which is perpendicular to the optical axis of the receiver. With this arrangement the image of an object on the axis of the transmitter will always be sharply focused on to the plane 104 at a position dependent on the range of the object.