Exposure meter employing photodiode

Claim 2

An exposure control system for use in photographic work, said system comprising a field-effect transistor having a gate terminal, and source and drain terminals, a photodiode connected between said gate terminal and a junction, a variable resistor connected between said source terminal and said junction, said variable resistor being interconnected to at least one determining exposure factor, to vary its resistance in response to setting of said at least one of said exposure factors and a battery connected between said junctions and said drain terminal.

Claim 3

An exposure control system according to claim 1, wherein a current indicating device is connected in series with said battery between said junction and said drain terminals.

Claim 4

An exposure control system according to claim 1, wherein a temperature responsive device is connected in series with said variable resistor between said source terminal and said junction.

Claim 5

An exposure control system according to claim 1, wherein a constant current circuit is connected in parallel with said field-effect transistor and wherein a current indicating device is connected between the drain terminal of said transistor and said constant current device.

Claim 6

An exposure control system according to claim 1, wherein a second field-effect transistor is connected with its drain and source terminals in parallel with the first field-effect transistor across said battery, wherein the gate terminal of said second field-effect transistor is connected to said junction and wherein a current indicating device is connected between the drain terminals of the two transistors.

Claim 7

An exposure control system according to claim 5, wherein said current indicating device is connected across a difference amplifier formed of a pair of transistors, the base terminals of which are connected respectively to the drain terminals of the field-effect transistors.

Claim 8

An exposure control system according to claim 6, wherein a temperature compensating circuit is provided including a first transistor having its collector and emitter terminals connected in series with said variable resistor between the source terminal of said first field-effect transistor and said junction and a second transistor having its collector and emitter terminals connected in series between said difference amplifier and said junction and means connecting the base terminals of first and second transistors to the collector terminal of the first transistor.

Claim 9

An exposure control system according to claim 1, wherein the anode of said photodiode is connected to the gate terminal of said field-effect transistor and the cathode of said photodiode is connected to said junction.

Claim 10

An exposure control system according to claim 1, wherein a second field-effect transistor which has a polarity Opposite to that of said field-effect transistor is connected in series with a temperature compensating diode across the battery to provide a constant current circuit and wherein one end of said photoconductive diode is connected to the drain of said second field-effect transistor while the other end of said photoconductive diode is connected to the gate of said first field-effect transistor.

Claim 11

An exposure control system according to claim 1 wherein a second field-effect transistor is connected in parallel with the first field-effect transistor, wherein a current indicating device is connected between the drain terminals of the first and second field-effect transistors and wherein a third field-effect transistor which as a polarity opposite to that of said first field-effect transistor is connected in series with a temperature responsive diode across said battery to provide a constant current circuit, the drain terminal of said third field-effect transistor being connected to the gate terminal of the first field-effect transistor.

Claim 12

An exposure control system in a camera, comprising a first field-effect transistor having a gate, source and drain terminals; a photodiode adapted to receive light from an object to be photographed; one end of said photodiode being connected to said gate terminal; a battery connected between said drain terminal and the other end of said photodiode; a variable resistor connected between said source terminal and the first junction between said battery and said other end of said photodiode, said variable resistor being interconnected to at least one exposure determining factor, so that the combination of the brightness of the object to be photographed and said exposure factors obtains a proper exposure when the amount of current flowing through said source and drain terminals becomes a predetermined value.

Claim 13

An exposure control system in a camera, comprising a first field-effect transistor having a gate, source and drain terminals; a photodiode adapted to receive light from an object to be photographed; one end of said photodiode being connected to said gate terminal; a battery connected between said drain terminal and the other end of said photodiode; a variable resistor connected between said source terminal and the first junction between said battery and said other end of said photodiode, said variable resistor being interconnected to at least one exposure determining factor, so that the combination of the brightness of the object to be photographed and said exposure factors obtains a proper exposure when the amount of current flowing through said source and drain terminals becomes a predetermined value.

Claim 14

An exposure control system according to claim 11, further comprising an indicating device controlled by said current flowing through said drain and source terminals for indicating the proper exposure.

Claim 15

An exposure control system according to claim 12, wherein said indicating device is connected to the drain-source circuit.

Claim 16

An exposure control system according to claim 12, further comprising a temperature responsive device connected in series with said variable resistor between said source terminal and said first junction.

Claim 17

An exposure control system according to claim 14, further comprising a first resistor connected between said drain terminal and said battery; a second and third resistors; and a second field-effect transistor having a gate terminal connected to said first junction, a drain terminal connected through said second resistor to the second junction between said battery and said first resistor, and a source terminal connected to the first junction through said third resistor, said indicating device being connected between said drain terminals of said first and second field-effect transistors.

Claim 18

An exposure control system according to claim 15, wherein said temperature responsive device is a first transistor of which collector and base terminals are connected to each other and of which emitter terminal is connected to said first junction, and further comprising a differential amplifier including a pair of transistors of which base terminals are connected respectively to the drain terminals of said first and second field-effect transistors, emitter terminals are connected to each other and of which collector terminals each are connected to said second junction through a resistor, and an additional transistor of which collector terminal is connected to said emitter terminals of said pair, emitter terminal is connected to said first junction and of which base terminal is connected to said collector and base terminals of said first transistor.

Claim 19

An exposure control system according to claim 12, further comprising a second field-effect transistor having polarity opposite to that of said first fieLd-effect transistor and connected across said battery to provide a constant current circuit, the drain terminal of said second field-effect transistor being connected to the other end of said photodiode; and a temperature compensating diode connected between said battery and the junction between said drain terminal of said second field-effect transistor and the other end of said photodiode.

Claim 20

An exposure control system according to claim 12, further comprising a first resistor connected between said drain terminal and said battery; a second and third resistors; a second field-effect transistor having a gate terminal, a drain terminal connected through second resistor to the second junction between said battery and said first resistor, and a source terminal connected to the first junction through said third resistor; a third field-effect transistor having polarity opposite to that of said first field-effect transistor and connected across said battery to provide a constant current circuit, the drain terminal of said third field-effect transistor being connected to the gate terminal of said second field-effect transistor; and a temperature compensating diode connected between said battery and the junction between said drain terminal of the third field-effect transistor and said gate terminal of said second field-effect transistor, said indicating device being connected between the drain terminals of said first and second field-effect transistor.