Long time exposure preventing device for camera with electronic flash

Abstract

A signal indicating that the correct exposure value has been achieved and a signal indicating the completion of flash are logically summed to provide a shutter closing signal. This ensures that the shutter will be closed even when the light emitted by the flash is insufficient to achieve the proper level of exposure.

What is claimed is: 
     
       1. In a camera system having a shutter mechanism, a light measurement system to generate a shutter closing signal in response to a correct exposure signal indicative of a correct exposure value, an electronic flash to emit a flash of light in synchronism with the opening of the camera shutter and to suspend the flashing operation in response to a .[.shutter closing.]. .Iadd.said correct exposure .Iaddend.signal, the improvement comprising: logic means for generating a flashing operation signal indicative of the completion of the flash operation, and for generating said shutter closing signal by a logical sum operation of the .[.corrct.]. .Iadd.correct .Iaddend.exposure signal and the flashing operation signal. 
     
     
       2. The camera system of claim 1 wherein said light measurement system includes first logic means for delivering a correct exposure signal output indicative of a correct exposure for a given light intensity and a given film sensitivity, and wherein said logic means to generate said shutter closing signal comprises second logic means for inverting a signal indicative of flash emission by said electronic flash and producing said flashing operation signal as an output thereof and third logic means receiving the outputs of said first and second logic means and providing an output to close the shutter mechanism. 
     
     
       3. The camera system of claim 2 wherein said light measurement system further comprises means for measuring light into the camera, an operational amplifier, said means for measuring being coupled across the inputs of said amplifier for zero biasing, integrating means receiving the output of said means for measuring and delivering an output with said amplifier, resistor means adjustable to film sensitivity and comparator means responsive to said resistor means and said output of said amplifier and integrating means for producing a correct exposure signal indicative of proper shutter opening time for a correct exposure. 
     
     
       4. The camera system of claim 2 wherein said second logic means comprises an inverter for inverting a signal level indicative of the emission of said electronic flash. 
     
     
       5. The camera of claim 2 wherein said third logic means comprises an OR gate receiving outputs of said first and second logic means to close said shutter .[.mechanisn.]. .Iadd.mechanism .Iaddend.and wherein said shutter mechanism comprises magnet means operable with a bottom curtain of said shutter mechanism and said OR gate generates an output to selectively deenergize said magnet means. 
     
     
       6. The camera system of claim 5 wherein said second logic means comprises an inverter for inverting a signal level indicative of the emission of said electronic flash and delivering an output to one input of said OR gate. 
     
     
       7. The camera system of claim 6 wherein said first logic means comprises an operational amplifier, means for measuring light into the camera and delivering an output in response thereto, integrating means receiving the output of said measuring means, an adjustable resistor providing an output indicative of film sensitivity, and comparator means receiving as one input the amplifier and integrating means signals and as a second input the signal from said resistor, said comparator producing an output signal to said OR gate indicative of proper shutter opening time for a correct exposure. 
     
     
       8. The camera system of claim 7 wherein the output of said first logic means is delivered to said flash unit to terminate the emission of light therefrom. 
     
     
       9. The camera system of claim 2 wherein the output of said first logic means is provided to said flash unit to terminate the emission of light therefrom. 
     
     
       10. The camera system of claim 1 further comprises switch means to initiate operation of said first logic means. .Iadd. 11. A camera system, comprising; means for generating a correct exposure signal indicative of a correct exposure value, flash means for emitting a flash of light, and including flash triggering means, flash stopping means, and an output, said correct exposure signal being applied as an input to said flash stopping means, means connected to said output for producing a signal indicative of the completion of a flash operation, and logic means for forming a logical sum of said flash operation completion signal and said correct exposure signal to generate a shutter closing signal. .Iaddend..Iadd. 12. A camera system, comprising; means for generating a correct exposure signal indicative of a correct exposure value, flash means for emitting a flash of light, and including flash triggering means, flash stopping means, and an output, said correct exposure signal being applied as an input to said flash stopping means, means connected to said output for producing a signal indicative of the completion of a flash operation, and means for generating a shutter closing signal in response to said correct exposure signal and said flash operation completion signal. .Iaddend. .Iadd. 13. A camera system, comprising: a shutter mechanism which closes in accordance with a shutter closing signal;   means for generating a correct exposure signal;   flash means for performing a flashing operation to generate a flash of light;   means for generating a flash operation signal indicative of the completion of said flashing operation; and   means for forming a logical sum of said correct exposure signal and said flash operation signal to form said shutter closing signal. .Iaddend..Iadd. 14. A camera system as claimed in claim 13, further comprising means for terminating said flashing operation in response to said correct exposure signal. .Iaddend. .Iadd. 15. A camera system as claimed in claim 13, wherein said logic means comprises OR gate means, said shutter mechanism including magnet means, and said shutter closing signal being applied to said magnet means to effectuate shutter closing. .Iaddend..Iadd. 16. A camera system as claimed in claim 13, wherein said correct exposure signal generating means comprises an operational amplifier having inputs and light measuring means coupled across said inputs of said amplifier, integrating means receiving an output of said light measuring means and delivering an output with an output of said amplifier, resistor means adjustable to film sensitivity, and comparator means responsive to said resistor means and a combined output of said amplifier and said integrating means, said comparator means producing said correct exposure signal at an output thereof. .Iaddend..Iadd. 17. A camera system as claimed in claim 13, wherein said flash means includes an output terminal for providing a signal in accordance with the charge on said main capacitor, said means for generating said flash operation signal comprising inverter means for receiving and inverting the signal at said output terminal. .Iaddend. .Iadd. 18. A camera system as claimed in claim 17, wherein said flash means comprises flash triggering means for initiating said flashing operation in response to the operation of a synchro switch, and flash stopping means for terminating said flashing operation in response to said correct exposure signal. .Iaddend..Iadd. 19. A camera as claimed in claim 18, wherein said flash means further comprises a main capacitor and a power supply for charging said main capacitor, said flash stopping means and said flash triggering means being arranged in parallel with said main capacitor. .Iaddend..Iadd. 20. A camera system as claimed in claim 18, wherein said flash triggering means comprises a flash discharge tube for discharging the charge on said main capacitor to emit light, a transformer for triggering said flash discharge tube and a capacitor coupled between said transformer and said synchro switch. .Iaddend..Iadd. 21. A camera as claimed in claim 18, wherein said flash triggering means includes a flash discharge tube for discharging the charge on said main capacitor to emit light, said flash stopping means comprising means for receiving said correct exposure signal, bypass means connected in parallel with said flash discharge tube, and means for rendering said bypass means conductive in response to said correct exposure signal. .Iaddend. .Iadd. 22. A camera system, comprising, in combination, a camera having a light measurement system, and an electronic flash for emitting a flash of light; said camera including a shutter mechanism, said light measurement system generating a shutter closing signal in response to a correct exposure signal indicative of a correct exposure value, said electronic flash including an input terminal for receiving said correct exposure signal and means for terminating said flash of light in response thereto, said electronic flash further including an output terminal for delivering an output signal indicative of the completion of a flash operation, and said light measurement system further including means for generating said shutter closing signal in response to said electronic flash output signal. .Iaddend..Iadd. 23. A camera system, comprising, in combination, a camera and an electronic flash;   said camera including: means for generating a correct exposure signal indicative of a correct exposure value, an output terminal for delivering said correct exposure signal to said flash, and means for generating a shutter closing signal in response to either said correct exposure signal or a flash output signal indicative of the completion of a flash emission;   said electronic flash including: an input terminal for receiving said correct exposure signal, means for terminating a flash emission in response to said correct exposure signal, means for providing said flash output signal indicative of the completion of a flash emission, and an output terminal for delivering said flash output signal to said camera. .Iaddend..Iadd. 24. A camera system comprising the combination of a camera and a flash unit, said camera including means for generating a correct exposure signal, and means for generating a shutter closing signal in response to one of said correct exposure signal and a flash output signal; said flash unit including an input for receiving said correct exposure signal, means for terminating a flash emission in response to said correct exposure signal and means for providing said flash output signal, said output signal being indicative of the completion of a flashing operation.