Exposure control apparatus for photographic cameras

Claim 2

In an exposure-control circuit for controlling exposure in a camera, comprising a photoconductive cell for measuring the intensity of light reflected from an object being photographed, and a flash unit being operated at a given instant to illuminate the object, the improvement comprising: A. a switch means for providing power to operate the lamp, and B. a timing circuit for operating said switch means to cause the lamp to illuminate said cell again when a predetermined time has passed since said given instant, whereby sufficient additional light is provided to the photoconductive cell to cause the exposure-control circuit to terminate said exposure after said predetermined time, even if said reflected light is insufficient to terminate the exposure.

Claim 3

An exposure control apparatus for a photographic camera comprising: A. a photoconductive cell, B. a power source connected to said photoconductive cell, C. a power source switch connected to said power source, D. a luminescing member disposed opposite said photoconductive cell and connected to said power source, E. a first fixed terminal connected to said luminescing member, F. a movable terminal connected to said power source via said power source switch and means to connect it to said first fixed terminal upon a shutter release operation to light up said luminescing member, thereby preliminary irradiating said photoconductive cell, G. an external luminescent means connected to said movable terminal, H. a second fixed terminal connected to said external luminescent means and means to connect it to said movable terminal synchronously with a shutter-blade opening action, I. a first transistor having a collector electrode connected to said luminescing member and the emitter electrode connected to said movable terminal, and operable to effect switching to light up again said luminescing member after a predetermined time, J. a first resistor connected between the collector electrode and a base electrode of said first transistor, and K. a first capacitor connected between the emitter electrode and the base electrode of said first transistor, and constituting a timing circuit with said first resistor for controlling said predetermined time, whereby sufficient additional light is provided to the photoconductive cell to cause the exposure-control circuit to terminate said exposure after said predetermined time, even if a reflected light is insufficient to terminate the exposure.

Claim 4

An exposure control apparatus for a photographic camera comprising: A. a photoconductive cell, B. a power source connected to said photoconductive cell, C. a power source switch connected to said power source, D. a luminescing member disposed opposite said photoconductive cell and connected to said power source, E. a first fixed terminal connected to said luminescing member, F. a movable terminal connected to said power source via said power source switch and means to connect it to said first fixed terminal upon a shutter release operation to light up said luminescing member, thereby preliminary irradiating said photoconductive cell, G. an external luminescent means connected to said movable terminal, H. a second fixed terminal connected to said external luminescent means and means to connect it to said movable terminal synchronously with a shutter-blade opening action, I. a first transistor having a collector electrode connected to said luminescing member and the emitter electrode connected to said movable terminal, and operable to effect switching to light up again said luminescing member after a predetermined time, J. a first resistor connected between the collector electrode and a base electrode of said first transistor, and K. a first capacitor connected between the emitter electrode and the base electrode of said first transistor, and constituting a timing circuit with said first resistor for controlling said predetermined time, whereby sufficient additional light is provided to the photoconductive cell to cause the exposure-control circuit to terminate said exposure after said predetermined time, even if a reflected light is insufficient to terminate the exposure.

Claim 5

An exposure control apparatus according to claim 2, further comprising a variable resistor connected between said luminescing member and said first fixed terminal.

Claim 6

An exposure control apparatus according to claim 2, further comprising a switch connected between said power source switch and the emitter electrode of said first transistor, said further switch being closed upon the attachment of said external luminescent means to said camera.

Claim 7

An exposure control apparatus according to claim 2, in which said first resistor is a variable resistor.

Claim 8

An exposure control apparatus according to claim 2, further comprising: A. a semiconductor switching element having an anode electrode connected to said photoconductive cell and a cathode electrode connected to said luminescing member, and B. a second resistor connected between the gate electrode of said semiconductor switching element and said second fixed terminal.

Claim 9

An exposure control apparatus according to claim 6, in which said semiconductor switching element is a silicon controlled rectifier, and said apparatus further comprises a third resistor and a second capacitor connected in series with each other and in parallel with said second resistor.

Claim 10

An exposure control apparatus according to claim 2, further comprising: A. a second transistor having a collector electrode connected to said power source and an emitter electrode connected to said luminescing member, B. a fourth resistor connected between the base electrode and the collector electrode of said second transistor, C. a third transistor having a collector electrode connected to a base electrode of said second transistor and an emitter electrode connected to said power source via said power source switch, D. a third capacitor connected between the base electrode and the emitter electrode of said third transistor, E. a fourth transistor having a collector electrode and an emitter electrode connected respectively to the base electrode and the emitter electrode of said third transistor, F. a fifth resistor connected between said fourth resistor and the collector electrode of said fourth transistor and G. a sixth resistor connected between said second fixed terminal and the base electrode of said fourth transistor.