GB1354030A - Range finding system - Google Patents

Abstract

1354030 Automatic focusing CANON KK 27 May 1971 [27 May 1970 (3)] 17580/71 Heading H4D In an automatic focusing system, based on triangulation principles and in which a lightbeam is directed on to the object to be focused and the light reflected therefrom directed on to a photodetector in a position thereon indicative of the object's range, the optical means directing the reflected light is such that the reflected light range formed on the detector has an elongated shape. This is stated to improve the sensitivity of the system. In Fig. 1, a spherical or parabolic mirror 2 directs light from a bulb 1, incorporating a condenser 3, on to the object via colour or I.R. filter 4. The reflected light, after filtering at 7 is formed into a flat beam by cylindrical lens 8 and as such is directed by fixed mirror 9 and mirror 10, coupled to a focusing lens 13, on to differential photodetectors 11a, 11b. The differential output of the detectors is used to energize focusing motor 17 and adjust lens 13 until mirror 10 directs the line image on to the abutting line C between the detectors. To help in identifying the reflected light, the transmitted beam may be chopped and the differential detector outputs fed to two synchronous detectors (one via a phase inverter), the chopper actuating signal being used as the synchronous detector's reference whereby only one of the synchronous detectors gives an output dependent on the sense of the out of focus. The outputs of the two photodetectors may be summed, or a separate photodetector used to give a signal indicative of the intensity of the reflected light and produce a corresponding correction to the brightness of the source. If the brightness falls, indicating that the object is near infinity the motor is energized to move the lens to infinity focusing. In a concentric arrangement, Fig. 4, the reflected light is reflected by spherical reflector 18 on to axially movable photodetector pairs 11a, 11b, via optical wedges 19 forming the elongated images. Only one photodetector is necessary, Fig. 6, if a triangular mask 20, Fig. 8, is placed in front of it and the upper and lower reflected beams from cylindrical lenses 8a, 8b alternately applied thereto by means of shutter 24. To assist in the formation of the elongated image, the transmitted beam may be flat, using a linear filament bulb with no condenser, Fig. 10 (not shown), or a slit mask in front of the bulb.