Patent GB-533876-A (GB)
Title: Improvements relating to automatic focussing devices for cameras
IPC: G03B19/18
Filed: 1939-12-07
Abstract: 533,876. Photo-electric range finder for automatically focusing cameras. HUITT, L. H. Dec. 7, 1939, No. 31742. [Class 40 (iii)] [Also in Group XX] A photo-electric apparatus for automatically focusing a television or other camera especially of the kind described in Specification 516,486, [Group XX], comprises means for projecting a beam of highfrequency pulsating light from a point near the camera lens in any desired direction, and a detector displaced laterally from the camera for forming an image of the illuminated part of the field of view on a photo-electric cell device responsive to the pulsating light and in correspondence with the parallactic displacement of the image for automatically focusing the camera. In the camera shown, light from a lamp 96, Fig. 4, is projected by a lens 98 to mirror 102 and thence to mirrors 104, 106, Fig. 1. The mirror 106 is situated in front of the lens 14 between the two mirrors 20, 22, Fig. 3, which in conjunction with other mirrors 18, 28, 16 direct two separate views of the same object into the lens 14 as described in Specification 516,486. A disc 110, Fig. 4, formed with perforations 108, Fig. 5, is rotated by a motor driven shaft 112 to produce pulsations in the light beam. The mirror 104 is mounted in a gymbal ring 206 which can be adjusted to vary the direction of the beam, which after reflection from the mirror 106 always appears to issue from a point in the lens 14. The pulsating light returning from the object on which it is directed is received by a mirror 120 at the side of the camera and is reflected thereby to pass through a lens 124 to a mirror 128 and thence to two cones of glass 130 having juxtaposed bases 126 and separate truncated small ends 136 directed towards a photo-electric cell 146. The mirror 120 is formed with horizontal corrugations, or the mirror 120 or the lens 124 is cylindrically curved to cause the image thrown on the photo-electric cell to be in the form of a narrow vertical line. The position of this image on the base 126 of the cones 130 and therefore the relative amount of light transmitted by the cones is a function of the distance of the object from the camera and is detected as follows. The rotating disc 110 is formed with two sets of apertures 142, 144 which expose the cell 146 to the two cones 130 alternately. The cell output is amplified by amplifiers 148, 150, Fig. 8, rectified and smoothed by device 152, and passed through a commutator 156 to the armature coils 82, 84. The commutator 156 is driven by the shaft 112 in synchronism with the disc 110 so that the impulses of the cell derived from one cone is passed to one coil 82 or 84 and the impulses derived from the other cone to the other coil. The armature 58, Fig. 1, carrying these coils between opposite magnetic poles therefore turns to an angular position depending on the distance of the object from the camera. The various devices of the camera requiring adjustment for focusing the camera on the object are automatically derived from the armature 58. This armature drives bevel gearing 54, 52 connected to gearing 48, 46 which adjust the camera lens 14 and the view finder lens 36 as described in Specification 516,486. The armature also turns a cam 60 for controlling the angular position of the mirrors 20, 22. In the present arrangement, these mirrors, which are pivoted at 24, 26 are connected by links 70, 72, Fig. 2, to two levers 66, 68 bearing on two cam faces on the cam 60 ; and these two cam faces are varied longitudinally in opposite directions to take account of the lateral angular direction of the illuminated object. As in Specification 516,486, " forveal " screens 32, Fig. 7, are provided for each lens 14, 36, each such screen having an aperture in a graded optical surround. These screens are carried by rods 188 connected by cables 194, pulleys 202 and a double sector 196 itself connected by cables 192 to rods 182, 184 attached to a plate 178 connected by a ball joint 174 and a rod 172 sliding therein to a hand lever 166, Fig. 6, which can be adjusted about a universal joint 170 as described in Specification 516,486 but has no rotational movement about its axis for focusing, the focusing being now automatic as described above. The movements of the hand lever 166 are also transmitted to other devices requiring corresponding adjustment. The movements are transmitted by cable mechanism to sliding rods 220, Fig. 1, connected by a ball joint 214 and a rod 212 sliding therein to the gymbal 206 of the mirror 104, so that the light beam is directed to the object the image of which appears in the apertures 34 of the " forveal " screens. Another cable mechanism 234 transmits the lateral movements to a cam 230, Fig. 4, co-operating with an arm 224 on the mirror 120 pivoted at 222, and still another cable mechanism 244 transmits the lateral movements to a lever 240 which determines the longitudinal position of the cam 60 on the shaft 56 and therefore the part of the cam which co-operates with the levers 66, 68 of the linkwork for adjusting the mirrors 20, 22.