Patent GB-1246655-A (GB)
Title: Automatic flash apparatus for use with a camera
Inventor: METZ PAUL
IPC: G03B7/16
Filed: 1968-12-04
Abstract: 1,246,655. Electronic flash-guns. P. METZ. Dec.4, 1968 [Dec.28, 1967; Feb. 2, 1968; March 30, 1968; April 18, 1968; May 11, 1968; June 11, 1968], No.57535/68. Heading G2A. Automatic flash apparatus, for use with a camera 1, includes a flash unit 11; a flash limiting device 6 having a photo-electric element 4 arranged to respond to the light reaching the camera from the subject being photographed and connected to terminate the light emission by the unit 11 in response to the light received by the element 4, and power energy supply means 3 connected to deliver flash-triggering energy to the flash unit; the apparatus being arranged so that the flash limiting device 6 is connected with the flash unit 11 to become operative only upon initiation of a light-flash by said unit. The flash limiting device 6 comprises control voltage producing means electrically connected to the element 4, shown as a photodiode 24 in Fig. 2, and including a capacitor 25 for producing a voltage proportional to the time integral of the intensity of the light received by said element 24 from the instant of commencement of a flash by said unit, and a resistor 27 for producing a voltage proportional value of the intensity of the light received by the photo-electric element, the latter voltage serving to compensate for inherent time delays in the response of the device 6, and both voltages being added together to form a control voltage which, upon receiving a predetermined value, actuates the device 6 to terminate the light flash being produced by the flash unit. Setting means 13 are provided for adjusting the responsivity of the device 6 in accordance with the sensitivity of the film used and camera lens aperture being employed. A synchronizing contact provided in the camera 1 initiates operation of an amplifier 5, of the photocell 4 and triggering of the flash unit 11. This results in the simultaneous generations of the voltages for feeding the light meter and flashlimitation device, Fig. 2 showing a circuit permitting the generation of such voltages directly from the discharge of a capacitor 17 when synchronizing switch 18 is actuated. This creates a voltage surge in a primary winding 161, which in turn induces a voltage pulse in a secondary winding 162 to trigger a flash-tube 14, and simultaneously creates a voltage surge in a tertiary winding 163 so as to charge a storage capacitor 22 and thus provide the supply voltage for the light meter arrangement. Another embodiment of a storage capacitor charging sub-circuit is shown in Fig.3 (not shown), while an alternative way of producing a voltage to trigger and operate the light meter and flash limitation device utilizing an impedance (42) is illustrated in Fig. 4 (not shown). In Fig. 5 (not shown), a similar light responsive device to that of Fig. 2 is shown, but a modified triggering device for the flash limiting tube 15 (the quench tube) is provided. Two transistors (48, 49) Fig. 6, (not shown) may be utilized if the control power supplied to a transistor 20 is insufficient to switch the transistor quickly and completely. Changing the capacitance value of the integrating capacitor, e.g. by providing five stages (250-254) Fig. 7, (not shown), results in a potentiometer (29) being employed to achieve a fine control of an amplifier (50). Figs. 9-12, (not shown), illustrate one embodiment of a setting unit for use with the circuit of Fig. 2, while Fig. 13 (not shown) illustrates one example of a time lag compensating circuit.