Patent GB-733389-A (GB)
Title: Improvements in or relating to control devices for optical objectives of variable focal length
IPC: G02B15/02
Filed: 1953-04-23
Abstract: 733,389. Lens mounts. MILLS, J. A., and TAYLOR, TAYLOR & HOBSON, Ltd. April 15, 1954 [April 23, 1953], No. 11270/53. Class 97 (1). In a variable focal length objective of the type in which " zoom " control for varying the equivalent focal length is effected by interrelated movement of two members of the objective and focusing for different object distances is effected by independent movement of one of the said members, the control device comprises a differential gear whose driving element is connected to the focusing member, focusing control means for operating one of the two driving elements of the differential gear, zoom control means for simultaneously operating the second driving element of the differential gear and the second movable member of the objective, and a shaped cam forming part of the operative connection between such second driving element and such second movable member for determining the relationship between the movements of the two movable members of the objective. The invention is described as applied to the objective disclosed in Specification 689,206 and comprising a front positive element A, Fig. 1, and an adjacent netative element B movable relative to each other and to a fixed rear member C to effect variation of focal length, the element A being movable independently for focusing. As shown in Figs. 1 to 2 the element A is in a mount A<SP>1</SP> supported on a shaft F supported for longitudinal movement on rollers F<SP>1</SP> and having a bracket F<SP>2</SP>carrying rollers F<SP>3</SP> resting upon a second parallel bar G slidably supported in V-shaped guides G<SP>2</SP>, the bars F and G respectively carrying racks F<SP>4</SP> , G<SP>3</SP> both engaged by a pinion H<SP>1</SP> freely rotatable on a hollow rod H slidable along a fixed spindle H' and prevented from rotating by a pin slot arrangement. The racks and pinion H<SP>1</SP> form a differential gear. The rod H carries a follower roller H<SP>6</SP> engaging a shaped cam groove J<SP>1</SP> framed on a hollow drum J which is rotatable in ball bearings J<SP>2</SP> and is driven by engagement of a worm wheel J' thereon with a worm L rotated by an electric motor L<SP>2</SP> via a belt L<SP>1</SP>. Carried within the drum J are gear teeth J<SP>3</SP> engaging a gear K<SP>1</SP> on a quick-pitch screwthreaded shaft K engaged by a nut B<SP>1</SP> fixed to the carriage B<SP>2</SP> of the second movable lens B. To effect change of focal length, therefore, the motor L<SP>2</SP> is energized to rotate the drum J. This moves the lens B by way of the shaft K and gears K<SP>1</SP> and J<SP>3</SP> and, by means of the cam groove J<SP>1</SP>, causes longitudinal movement of the hollow rod H and of the pinion H<SP>1</SP> carried thereby. Since the rack G<SP>3</SP> is here held stationary the pinion H<SP>1</SP> causes the rack F<SP>4</SP> and with it the rod F to move and so cause movement of the lens A, co-ordinated with that of the lens B. To effect focusing control a motor M<SP>2</SP> (not shown) is energized to cause longitudinal movement of the shaft G and rack G<SP>3</SP> by rotating a screwthreaded shaft M<SP>1</SP>, Fig. 2, engaging a nut G<SP>4</SP> on the shaft G. Since, here, the hollow rod H is held stationary, movement of the rack G<SP>3</SP> causes rotation of the pinion H<SP>1</SP> and 'thence longitudinal movement of the shaft F and of the lens A, the lens B remaining stationary. Motors L<SP>2</SP> and N<SP>2</SP> may be controlled remotely by means of a potentiometer circuit. An iris diaphragm D, Fig. 1, located within the stationary lens member C, is operated by a gear ring D<SP>1</SP> driven by a shaft (not shown) operated by an electric motor which may be remotely controlled in the same manner as motors L<SP>1</SP> and M<SP>1</SP>.