Electronic circuits for automatic camera controls

Claim 2

In a camera, electrical circuit means for automatically determining the extent to which film in the camera is exposed, photosensitive means operatively connected to and forming part of said electrical circuit means for introducing into the latter an electrical signal according to the light intensity, and a closed loop circuit means also forming part of and connected with said electrical circuit means for controlling said electrical circuit means to determine the exposure in part according to the light intensity without being influenced by the characteristics of said photosensitive means, said closed loop circuit means including a logarithmic compression section connected in series with said photosensitive means, a logarithmic extension section also connected in series with said photosensitive means, and an amplifier connected between said sections and forming the closed loop circuit means with said logarithmic extension and compression sections, said electrical circuit means including a capacitor means electrically connected with said logarithmic extension section and a means electrically connected with said capacitor means for responding to a predetermined charge on said capacitor means for terminating an exposure, said closed loop circuit means applying to said capacitor means at said logarithmic extension section a constant charging current during exposure of film in the camera.

Claim 3

The combination of claim 1 and wherein said logarithmic extension section includes a transistor, a logarithmic compression element, and a voltage bias source all connected in series and said amplifier being electrically connected with said logarithmic extension section for operating as a negative feedback amplifier for controlling collector current of said transistor, said capacitor means being electrically connected in series with a collector of said transistor.

Claim 4

The combination of claim 2 and wherein a switch means forms part of said electrical circuit means for transmitting the constant charging current to said capacitor means, so that said switch means may be operated in conjunction with the operation of a mirror of a single lens reflex camera, said switch means being connected in parallel with said capacitor means for bypassing the latter except when saId switch means is opened, so that by opening the latter switch means in synchronism with the opening of a shutter of the camera, the charging of said capacitor means can commence simultaneously with the commencement of an exposure.

Claim 5

The combination of claim 2 and wherein said logarithmic compression section includes a diode and said logarithmic compression element of said logarithmic extension section also includes a diode, and said amplifier electrically interconnecting said diodes.

Claim 6

The combination of claim 4 and wherein said electrical circuit means includes a means for applying to said logarithmic extension section a linear voltage according to the size of the exposure aperture and the film speed, said electrical circuit means automatically determining the exposure time.

Claim 7

In a camera, electrical circuit means for automatically determining the extent to which film of the camera is exposed, photosensitive means operatively connected to and forming part of said electrical circuit means for introducing into the latter an electrical signal according to the light intensity, and a closed loop circuit means also forming part of and connected with said electrical circuit means for controlling said electrical circuit means to determine the exposure in part according to the light intensity without being influenced by the characteristics of said photosensitive means, said photosensitive means and said closed loop circuit means forming part of a storage section of said electrical circuit means, said storage section providing a first predetermined output voltage, said electrical circuit means including means for providing a second predetermined output voltage according to a given exposure aperture and film speed, a pair of differential circuit means forming part of said electrical circuit means and operatively connected therewith for receiving said first and second voltages as input voltages, respectively, said pair of differential circuit means providing a given output current, capacitor means forming part of said electrical circuit means to be charged with said latter output current, and said electrical circuit means including a means for terminating an exposure when said capacitor means is charged to a given extent, said storage section including a transistor having a collector circuit in which said photosensitive means is located, said storage section including an amplifier circuit, said means for providing said second predetermined output voltage including a variable resistor and a logarithmic conversion element connected in series therewith, said pair of differential circuit means respectively including two transistors which are symmetrically emitter-coupled with each other, said pair of differential circuit means providing said given output current in the form of a constant-current for charging said capacitor means.

Claim 8

In a camera, electrical circuit means for automatically determining the extent to which film of the camera is exposed, photosensitive means operatively connected to and forming part of said electrical circuit means for introducing into the latter an electrical signal according to the light intensity, and a closed loop circuit means also forming part of and connected with said electrical circuit means for controlling said electrical circuit means to determine the exposure in part according to the light intensity without being influenced by the characteristics of said photosensitive means, said photosensitive means and said closed loop circuit means forming part of a storage section of said electrical circuit means, said storage section providing a first predetermined output voltage, said electrical circuit means including means for providing a second predetermined output voltage according to a given exposure aperture and film speed, a pair of differential circuit means forming part of said electrical circuit means and operatively connected therewith for receiving said first and second voltages as input voltages, respectively, said pair of differential circuit means providing a given output current, capacitor means forming part of said electrical circuit means to be charged with said latter output current, and said electrical circuit means including a means for terminating an exposure when said capacitor means is charged to a given extent, said storage section including a transistor having a collector circuit in which said photosensitive means is located, said storage section including an amplifier circuit, said means for providing said second predetermined output voltage including a variable resistor and a logarithmic conversion element connected in series therewith, said pair of differential circuit means respectively including two transistors which are symmetrically emitter-coupled with each other, said pair of differential circuit means providing said given output current in the form of a constant-current for charging said capacitor means.

Claim 9

The combination of claim 6 and wherein said closed loop circuit means provides reference and control voltages in the circuit of said photosensitive means, and switching transistor means connected in parallel with said photosensitive means for assuming a non-conductive state when said voltages are approximately equal while assuming a conductive state when the difference between said voltages exceeds a predetermined threshold value.

Claim 10

The combination of claim 6 and wherein said transistor having its collector circuit containing said photosensitive means provides a collector current in said collector circuit which is inversely proportional to the inner resistance of said photosensitive means.

Claim 11

The combination of claim 6 and wherein said first predetermined output voltage forms a base voltage of said transistor which has said photosensitive means in its collector circuit.

Claim 12

The combination of claim 6 and wherein at least one logarithmic conversion element is connected in series with the emitter of said transistor in whose collector circuit said photosensitive means is located with the latter logarithmic conversion element being forwardly coNnected, and said logarithmic conversion element which is in series with said variable resistor also being forwardly connected so that temperature dependency will automatically cancel.