Patent GB-1139342-A (GB)
Title: Improvements in or relating to apparatus for controlling the operation of a camera
Inventor: BARR JOHN DENZIL
IPC: G02B27/40
Filed: 1965-10-15
Abstract: 1,139,342. Lens mounts; automatic speed control. RANK ORGANISATION Ltd. Oct. 17, 1966 [Oct.15, 1965], No.43872/65. Headings G2J and G3R. [Also in Division H2] In focusing a television or other camera in which a driven element F2, Fig. 1, which moves the relevant lenses is controlled by a normally hand operated primary demand element A, in order to facilitate a rapid refocusing when the object distance is suddenly changed, an auxiliary demand element is provided which has been preset corresponding to the required new object distance and an electrical switch or mechanical device allows a changeover of control from the primary to the auxiliary demand element. As shown. Fig. 5, the primary demand element controls a tachogenerator B whose output is fed to a servo-device comprising a reversible electric motor G and tachogenerator G1 whose shafts G2, G3, are coupled together and drive through reduction gearing G4, the driven element F2. If the objective is of the zoom type, a potentiometer N is included whose tapping N1 is controlled by the zoom control member, as in Specification No. 1, 080, 011 so that the effective transmission ratio between the movements of the primary demand and driven elements depends on the position of the zoom control member. To effect rapid refocusing, a push button switch K is depressed and this places the electric motor G, under the control of the outputs of two equal potentiometers L, L1, energized from a D.C. source and connected in opposite senses, the tapping of potentiometer L being dependant on the position of a hand knob L4 forming the auxiliary demand element which has been previously preset, and the tapping of potentiometer L1 being dependant on the position of driven element F2, so that directly the driven element F2 reaches the new desired position, the outputs of potentiometers L, L1 cancel out and motor G stops. To prevent overshooting, a small damping voltage is applied through a high resistance J2 from the tachogenerator G1. In a modification, Fig. 3 (not shown), a plurality of auxiliary control circuits are provided, each with their own push button. To prevent the driven element F2 from moving at high speed against an end stop, a device may be incorporated as in Specification No. 1,080, 591 in which potentiometer 0 has its tapping 01 controlled by the position of the element F2 so that as the latter approaches either limiting position its speed is reduced. In a further form the speed of the reversible motor is determined, when the primary control device is in operation by the frequency of pulses generated by a pulse generator in accordance at least in part, with the speed of operation of the primary demand element. In a modification, Fig.6 (not shown), a handwheel (30) drives a shaft (32) connected to the lens focusing mechanism. When the handwheel (30) is released and a lever (40) moved so that a cam follower (38) thereon engages a heart-shaped cam (36), the shaft (32) and thus the lens focusing mechanism is moved to a position determined by the cam follower (38) reaching the re-entrant portion of the cam (36). The desired cam position is set initially either by a scale or by holding it in position by lever (40) whilst focusing by handwheel (30), a slipping clutch correction 34 between the cam (36) and shaft (32) allowing this. In further forms, stops are used instead of cams and two or more pre-set devices may be employed.