Shutter operating circuits for photographic cameras

Abstract

In a shutter operating circuit wherein the shutter time is controlled by a photoelectric transducer disposed to receive the light transmitting through the objective lens, there are provided a first amplifier for amplifying the output from the photoelectric transducer, a second amplifier having a high input impedance and operating to generate an output corresponding to the output from the first amplifier, means for feeding back the output from the second amplifier to the input of the first amplifier, a capacitor connected on the input side of the second amplifier for holding the output from the first amplifier in accordance with the opening operation of the shutter of the camera, a first impedance element connected in series with the photoelectric transducer, a second impedance element connected in parallel with the series combination of the first impedance element and the photoelectric transducer, an integrating capacitor for integrating the output from the second amplifier in accordance with the opening operation of the shutter, and a shutter trigger circuit for closing the shutter when the voltage across the integrating capacitor reaches a predetermined .[.valve.]. .Iadd.value .Iaddend.whereby the exposure time is determined by the output current from the second amplifier.

What is claimed is: 
     
       1. A shutter operating circuit for a photographic camera, comprising a photoelectric transducer disposed to receive .[.the.]. light .[.transmitting.]. .Iadd.transmitted .Iaddend.through the objective lens of said camera, first amplifier means for amplifying the output from said photoelectric transducer, second amplifier means having a high input impedance and operating to generate an output corresponding to the output from said first amplifier means, means for feeding back the output from said second amplifier means to the input of said first amplifier means, a capacitor connected on the input side of said second amplifier means for holding the output from said second amplifier means in accordance with the opening operation of the shutter of said camera, a first impedance element connected in series with said photoelectric transducer, a second impedance element connected in parallel with said series combination of said first impedance element and said photoelectric transducer, an integrating capacitor for integrating the output from said second amplifier means in accordance with the opening operation of said shutter, and a shutter trigger circuit for closing said shutter .[.when.]. .Iadd.upon .Iaddend.the voltage across said integrating capacitor .[.reaches.]. .Iadd.reaching .Iaddend.a predetermined value whereby the exposure time is determined by the output current from said second amplifier means .[.which.]. .Iadd.and .Iaddend.is proportional to the output from said photoelectric transducer and varied by utilizing the impedances of said first and second impedance elements as parameters. 
     
     
       2. The shutter operating circuit according to claim 1 wherein said first and second impedance elements comprise diodes having substantially the same characteristic. 
     
     
       3. The shutter operating circuit according to claim 1 wherein said first and second impedance elements comprise resistors having substantially the same characteristic. 
     
     
       4. The shutter operating circuit according to claim 2 .[.wherein.]. .Iadd.further including means for impressing .Iaddend.voltages corresponding to .[.informations.]. .Iadd.information .Iaddend.regarding the ASA sensitivity of the film utilized, iris opening or the like .[.are impressed.]. upon said first and second impedance elements so as to insert various .[.informations in.]. .Iadd.additional factors controlling .Iaddend.the shutter time. 
     
     
       5. The shutter operating circuit according to claim 1 wherein said first amplifier means comprises a differential amplifier circuit having an extremely high input impedance .Iadd.and said second amplifier means has an extremely high input impedance.Iaddend. . 
     
     
       6. A shutter operating circuit for a photographic camera, comprising a photoelectric transducer disposed to receive .[.the.]. light .[.transmitting.]. .Iadd.transmitted .Iaddend.through the objective lens of said camera for producing an output corresponding to the intensity of said light, an operational amplifier having a high input impedance .Iadd.and having said photoelectric transducer connected to the input thereof .Iaddend.for amplifying said output, a feedback circuit for feeding back the output of said operational amplifier to the input thereof, an integrating capacitor connected in said feedback circuit for integrating the output from said operational amplifier in an interlocked relation with the opening operation of the shutter of said camera, a first impedance element .Iadd.having an impedance Z 1  .Iaddend. connected in series with said photoelectric transducer .Iadd.to the input of said operational amplifier.Iaddend., a second impedance element .Iadd.having an impedance Z 2  .Iaddend. connected in parallel with the series combination of said photoelectric transducer and said first impedance element .Iadd.said first and second impedance elements being included in and comprising a part of the load on said feedback circuit.Iaddend., and a shutter trigger circuit connected to said integrating capacitor for closing said shutter when the voltage across said integrating capacitor reaches a predetermined value .[.whereby.]. .Iadd.thereby .Iaddend.to determine the exposure time in accordance with the .[.output.]. .Iadd.feedback current .Iaddend.from said operational amplifier which is proportional to the output of said photoelectric transducer .Iadd.in accordance with the expression ##EQU22## where I f  is the feedback current of the operational amplifier and I L  is the photocurrent of the photoelectric transducer and wherein the exposure time is varied dynamically .Iaddend.by utilizing the impedances of said first and second impedance elements as .[.the.]. parameters.[...]. .Iadd.in the feedback circuit and the accuracy of setting the exposure time in dark areas is improved. .Iaddend. 
     
     
       7. The shutter control circuit according to claim .[.5.]. .Iadd.6 .Iaddend.wherein said first and second impedance elements comprise diodes having substantially the same characteristic. 
     
     
       8. The shutter control circuit according to claim .[.5.]. .Iadd.6 .Iaddend.wherein said first and second impedance elements comprise resistors having substantially the same characteristic. 
     
     
       9. The shutter control circuit according to claim 6 .[.wherein.]. .Iadd.further including means for impressing .Iaddend.voltages representing .[.the informations.]. .Iadd.information .Iaddend.regarding the ASA sensitivity of the film used and the iris opening of the camera .[.are impressed.]. upon said first and second impedance elements.