Patent GB-573007-A (GB)
Title: Improvements in the operation of photographic camera shutters
IPC: G03B9/58
Filed: 1943-08-20
Abstract: 573,007. Photographic shutters. WOOD, A. F., and CELESTION, Ltd. Aug. 20, 1943, No. 13615. [Class 98 (i)] A photographic camera shutter is positively driven through its film- or plate-exposing position by a synchronous electric motor operated from alternating current mains to provide a known or predetermined relationship between the duration of exposure of the film or plate and the frequency of the current. As shown, the shutter comprises an apertured disc D and a blade member. The disc is mounted on a spindle and is geared by gearing G to the motor and on rotation the aperture A passes across the exposure aperture of the camera. The pivoted blade member is partly under control of the disc or motor and partly under the control of the operator so that it may be swung to make an exposure. A cam C associated with or geared to the disc D and contacts Cm1 are arranged so that prior to the passage of the aperture through exposure position a point in the circuit 1 is closed, and that shortly after such passage the point is again broken. The circuit 1 includes an electromagnet M, a source S of electrical energy, e.g. the secondary winding of transformer T, and contacts Co1 under control of the operator. The electromagnet M controls an armature on the pivoted blade member. A second circuit 2 includes the source S, an electromagnet R, contacts Cm2 controlled by the cam C and contacts Co2 controlled by the operator. When operated by closure of contacts Cm2 by cam C, the electromagnet R opens the contacts r1 in circuit 1 and closes contacts r2 to provide a holding circuit independent of the cam-operated contacts and dependent on the operator-controlled contacts Co2. To prevent exposure during movement of the film or plate from a position in which one area has been exposed to a position in which another area is to be exposed, the contacts Crll are opened as soon as the film or plate-moving mechanism is operated. The lamp L3 indicates that an exposure has been made and the lamp L1 that the motor is in operation. The circuit of L3 is controlled by electromagnet M through armature m3. In a modification, the aperture A effects the exposure, and the gearing is such that the time of movement of aperture A across the exposure aperture is appropriate. The selfstarting synchronous motor-operating disc D is only operative at the will of the operator. The disc D may be of conducting material with an insulating portion I, and co-operates with contacts Cm1 so that in the normal position of the disc, circuit 3 is open. Shortly after movement of disc D from its normal position, circuit 3 is closed until the disc makes a complete revolution. The circuit 1 includes operatorcontrolled contacts Co1 which, when closed, operate relay R to close contacts r2 in circuit 2 to connect the self-starting synchronous motor SM to the source of power. Movement of the disc D closes an alternative circuit for motor SM to ensure completion of a revolution for disc D. Cam-operated contacts may be provided to prevent exposure during movement of the film or plate. A number of cameras may have shutters of the type described, the gearing being such that the time of exposure in any one camera is the same at that in any other.