Patent GB-657294-A (GB)
Title: Improvements in and relating to cinematograph apparatus
IPC: G03B1/22
Filed: 1947-06-26
Abstract: 657,294. Kinematograph apparatus. BRITISH THOMSON-HOUSTON CO., Ltd. June 26, 1947, No. 16913. Convention date, July 25, 1940. [Class 97 (i)] [Also in Group XL (b)] Kinematograph film television apparatus is provided with means 'for displacing the film during an interval of time which is very short compared with the interval between successive television scans. In the arrangement shown in Fig. 1 in which an image of the film 3 is projected on to the signal plate 5 of a picture signal generating tube 6 displacement of the film is effected by means of dogs 14 which are caused to engage the film sprocket holes and to move downwardly by means of an arrangement comprising a lever arm 8 oscillating at high speed about a pivot point 9 under the control of a connecting rod 10 and crank 11 the rod carrying the dogs being slidingly carried by the lever 8 and arranged, by means of lever arm 20<SP>1</SP> operated by a cam 20, to project so as to engage the sprocket holes only when a member 22<SP>1</SP> is in the position shown in full lines. The member 22<SP>1</SP> is carried by a lever 22 coupled to a further lever 24 and arranged to operate, when the film loop 25 shortens, to cause member 22<SP>1</SP> to move into the position shown in dotted lines where it is inoperative to transmit the motion of the arm 20<SP>1</SP> to the dog carrying rod. With this arrangement a film speed of 24 frames per second may be employed with a television scanning rate of 25 frames per second the mechanism 22, 22<SP>1</SP>, 24 in co-operation with the loop 25 varying periodically to interrupt the film movement so that, in each second, one film frame is exposed twice (consecutively). In another embodiment (Fig. 2) applied to apparatus for recording television images on moving film, the film engaging dogs 64 are mounted on a leafspring 82 attached to a lever arm 58 pivoted at 59 which, together with a second identical lever 58b provided with a weight 82b equivalent to the weight of the dogs and leaf 82, forms a mechanical oscillatory system the resonance of which is made of the required frequency by means of springs 63, 63b. In operation an alternating motion is communicated to the system by means of a crosshead 84 connected to the levers by means of rods 83, 83b and caused to slide along the support plate 85 by means of a rod 60 and crank 61 this motion resulting in oscillation of the levers 58, 58b about axes 59, 59b so that the parts 82, 82b approach and move away from each other symmetrically in relation to the plate 85. During that part of the oscillatory cycle in which the parts move away from each other a rod 88, carrying a pusher device 90 normally urged by a spring 89 so that the device 90 causes the dogs to engage the film, is pulled towards the right, by the action of a lever 86 and cam 65, to free the dogs from engagement with the film (during the television scanning period) after which lever 86 releases the rod 88 and allows re-engagement of the dogs during that part of the oscillatory cycle in which the parts 58, 58b approach each other (during the television fly-back period) so that the film is moved downwardly due to the downward motion of the dogs. When the film frame rate differs from the television frame scanning rate the shortening of the film loop 75 operates contacts 92 to energize an electromagnet 91 which causes a device 72 to arrest the movement of the rod 88 for the desired period. In order to prevent exposure of the film frame, which is stationary in the gate during this period, to more than one television frame scanning a switch controlled by the device 72 is arranged to blank the scanning beam of the cathode-ray tube 56. In both of the embodiments a synchronous electric motor fed from a supply source having a frequency equal to a multiple of the television frame scanning frequency is employed as the motive power source. The oscillatory motion of the element 8 (Fig. 1) and of 58, 58b (Fig. 2) may be effected by electromagnetic means instead of by mechanical means. The apparatus may be employed to project images from kinematographic film on to a screen to serve as background scenes for a television transmission. Specifications 375,765 and 386,042 are referred to.