Patent GB-653850-A (GB)
Title: Improvements relating to optical range determining devices and apparatus
IPC: G01C3/08
Filed: 1948-03-23
Abstract: 653,850. Automatic control systems for lens. KALLMANN, H. E. March 23, 1948, No. 8500. Convention date, March 28, 1947. [Class 38 (iv)] [Also in Group XL (b)] Apparatus relating to optical focussing devices for automatic fine-focussing adjustment, or for use in range-finding, comprises a lens system with one or more light-intercepting means, each consisting of an opaque sheet with slits associated with a photo-electric cell, adapted to periodically intercept the imaging rays at one or more planes along the optical axis, thus producing a series of impulses which for each interceptor, have maximum amplitude when the interceptor is in the plane of the image. Automatic fine focusing.-Two semi-circular interceptor vanes 46, 47 (Fig. 5), mounted on a common spindle 50 and each containing a series of radial slots, are rotated by a motor 56 (Fig. 8) at a position such that the required image occurs between the vanes. A photo-cell 53 behind the vanes, passes the amplified and rectified impulses to the field winding of a D.C. motor 59, coupled to the focusing lens (not shown), a synchronous electronic switch 55 controlled by the motor 56 arranging that the impulses from each vane 46, 47 are fed to the field winding separately, in opposite directions. Thus the motor 59 will shift the focusing lens until the image is midway between the two vanes, when the net current in the field winding is zero. The interceptor slots 49 may be other than radial, e.g. inclined at Œ 45 degrees to the radii, and the axis of rotation of the vanes may be at an angle other than 90 degrees to the optical axis of the focusing lens. Automatic range-finder.-A shigle-turn helical interceptor (Fig. 11) or two half-turn helical interceptors (Fig. 12) may be used to explore a known part of the optical axis, a signal peak occurring once or twice in each revolution, when the slots are coincidental with the image. A timing pulse at the start of each revolution may be used to measure the distance of the object by noting the delay on a cathode-ray tube. Gating circuits may be added to eliminate unwanted images of objects at other distances. A circuit for measuring the distance of the focussed object includes a gas-filled triode 88 (Fig. 15) whose grid is controlled by the amplified, rectified and smoothed pulses derived from the photo-cell 84 and whose anode is fed with negative pulses from a synchronized pulse generator 83. Thus the valve is extinguished at the start of each revolution by the negative pulse from generator 83, and fired on receipt of an impulse from the photo-cell 84. The time that the valve is conducting is thus indicative of the distance of the object, and can be shown by a meter 91 in the anode circuit. Audible obstacle Locator.-The interceptor comprises a curved vane 97 (Fig. 17) with slots of varying width, so that the frequency of the impulses vary over the vane, and is indicative of the distance of the object. The varying frequency may also be produced by varying the speed of movement of the vane, or by a combination of both. The circuit of the complete apparatus (Fig. 18) includes a moving vane 97 producing impulses in a photo-cell 106, which are fed to a head-phone 110. The vane is made to oscillate by a vibrator circuit comprising coils 116 and contacts 101, which also produces the A.C. voltage that, when smoothed, supplies the H.T. for the electron multiplier 107. To avoid excessively high currents with intense light, a diaphragm 124 in front of the vane 97 is made photo-sensitive to provide a variable shunt across the H.T. supply.