Exposure meter having means for preventing erroneous metering

Claim 2

An exposure meter comprising, exposure detecting means including a photoelectric element, an electric power source, means connected with said photoelectric element to introduce exposure influencing factors thereinto, means connected with said photoelectric element and with said introducing means to produce a proper exposure signal, indicating means connected with said exposure detecting means and operable to indicate a proper exposure in response to a proper exposure signal, and means connected between said exposure detecting means and said indicating means to render said indicating means inoperable upon a predetermined condition of said source voltage, said signal producing means of said exposure detecting means comprising first and second signal producing means, said first signal producing means producing a first signal when the combination of said light intensity and said exposure influencing factors correspond to a proper exposure or an under-exposure, said second signal prodUcing means producing a second signal when said combination corresponds to a proper exposure or an over-exposure; said indicating means comprising first and second indicators, said first indicator being connected with said first signal producing means and operable in response to said first signal, said second indicator being connected with said second signal producing means and operable in response to said second signal; said means for rendering said indicating means inoperative including first and second voltage dividers and first and second transistors, said first voltage divider and said first transistor being connected between said first signal producing means and said first indicator, said second voltage divider and said second transistor being connected between said second signal producing means and said second indicator, whereby the operation of said first indicator alone indicates an under-exposure, the operation of said second indicator alone indicates an over-exposure, the operation of both said indicators indicates a proper exposure, and the inoperativeness of both said indicators indicates that said source voltage is lower than the minimum usable voltage level.

Claim 3

An exposure meter comprising: an electric power source; exposure detecting means connected with said electric power source and including a photoelectric element for receiving light from an object to be photographed, means connected with said photoelectric element to introduce exposure influencing factors thereinto, and means connected with said photoelectric element and with said introducing means to produce a proper exposure signal when the intensity of the light from the object and the exposure influencing factors provide a proper exposure; indicating means connected with said exposure detecting means and operable to indicate a proper exposure in response to said proper exposure signal from said exposure detecting means; means connected between said exposure detecting means and said indicating means to render said indicating means inoperative when the voltage of said electric power source has dropped below the minimum usable voltage level, said means for rendering said indicating means inoperative including at least one voltage divider connected between the opposite terminals of said electric power source, and at least one transistor having the collector thereof connected with one terminal of said electric power source via said indicating means, the emitter of said transistor being connected with the other terminal of said electric power source, the base of said transistor being connected with said voltage divider so that when said electric power source is at the minimum usable voltage level the voltage divided by said voltage divider and applied to said base is slightly higher than the threshold voltage between the base and emitter of said transistor.

Claim 4

An exposure meter comprising: an electric power source; exposure detecting means connected with said electric power source and including a photoelectric element for receiving light from an object to be photographed, means connected with said photoelectric element to introduce exposure influencing factors thereinto, and means connected with said photoelectric element and with said introducing means to produce a proper exposure signal when the intensity of the light from the object and the exposure influencing factors provide a proper exposure; indicating means connected with said exposure detecting means and operable to indicate a proper exposure in response to said proper exposure signal from said exposure detecting means; means connected between said exposure detecting means and said indicating means to render said indicating means inoperative when the voltage of said electric power source has dropped below the minimum usable voltage level, said means for rendering said indicating means inoperative including at least one voltage divider connected between the opposite terminals of said electric power source, and at least one transistor having the collector thereof connected with one terminal of said electric power source via said indicating means, the emitter of said transistor being connected with the other terminal of said electric power source, the base of said transistor being connected with said voltage divider so that when said electric power source is at the minimum usable voltage level the voltage divided by said voltage divider and applied to said base is slightly higher than the threshold voltage between the base and emitter of said transistor.

Claim 5

An exposure meter according to claim 2, wherein said signal producing means of said exposure detecting means comprises first and second signal producing means, said first signal producing means producing a first signal when the combination of said light intensity and said exposure influencing factors correspond to a proper exposure or an under-exposure, said second signal producing means producing a second signal when said combination corresponds to a proper exposure or an over-exposure; wherein said indicating means comprises first and second indicators, said first indicator being connected with said first signal producing means and operable in response to said first signal, said second indicator being connected with said second signal producing means and operable in response to said second signal; and wherein said means for rendering said indicating means inoperative includes first and second voltage dividers and first and second transistors, said first voltage divider and said first transistor being connected between said first signal producing means and said first indicator, said second voltage divider and said second trAnsistor being connected between said second signal producing means and said second indicator, whereby the operation of said first indicator alone indicates an under-exposure, the operation of said second indicator alone indicates an over-exposure, the operation of both said indicators indicates a proper exposure, and the inoperativeness of both said indicators indicates that said source voltage is lower than the minimum usable voltage level.

Claim 6

An exposure meter comprising: an electric power source; a bridge circuit having a photoelectric element for receiving light from an object to be photographed, a variable resistor serially connected to said photoelectric element for introducing exposure influencing factors, and two resistors serially connected to each other, said serially connected variable resistor and element being connected in parallel to said serially connected two resistors with respect to said source, said bridge circuit being adapted to be balanced when the resistance values of said element and said variable resistor correspond to a proper exposure, and to be un-balanced when the resistance values of said element and said variable resistor correspond to an improper exposure; a balance detecting circuit connected to said bridge circuit to produce a first signal upon balancing of the bridge circuit; indicating means connected to said balance detecting means, said indicating means being operable by said first signal to indicate the proper exposure; and means connected between said balance detecting means and said indicating means for rendering said indicating means inoperative when the voltage of said power source has dropped below the minimum usable voltage level, said rendering means including at least one voltage divider connected across the power source, and at least one transistor whose collector is connected to one terminal of said power source through said indicating means, whose emitter is connected to the other terminal of said power source, and whose base is connected to said voltage divider so that when said power source is at the minimum usable voltage level, the voltage divided by said voltage divider and applied to said base is slightly higher than the threshold voltage between the base and emitter of said transistor.

Claim 7

An exposure meter comprising: an electric power source; a bridge circuit having a photoelectric element for receiving light from an object to be photographed, a variable resistor serially connected to said photoelectric element for introducing exposure influencing factors, and two resistors serially connected to each other, said serially connected variable resistor and element being connected in parallel to said serially connected two resistors with respect to said source, said bridge circuit being adapted to be balanced when the resistance values of said element and said variable resistor correspond to a proper exposure, and to be un-balanced when the resistance values of said element and said variable resistor correspond to an improper exposure; a balance detecting circuit connected to said bridge circuit to produce a first signal upon balancing of the bridge circuit; indicating means connected to said balance detecting means, said indicating means being operable by said first signal to indicate the proper exposure; and means connected between said balance detecting means and said indicating means for rendering said indicating means inoperative when the voltage of said power source has dropped below the minimum usable voltage level, said rendering means including at least one voltage divider connected across the power source, and at least one transistor whose collector is connected to one terminal of said power source through said indicating means, whose emitter is connected to the other terminal of said power source, and whose base is connected to said voltage divider so that when said power source is at the minimum usable voltage level, the voltage divided by said voltage divider and applied to said base is slightly higher than the threshold voltage between the base and emitter of said transistor.

Claim 8

An exposure meter according to claim 4, wherein said balance detecting circuit includes a first transistor and a second transistor complementary to said first transistor, both said first and second transistors being non-conductive upon balancing of said bridge circuit, either one of the first or second transistors being non-conductive upon un-balancing of the bridge circuit, said non-conductivity of both said first and second transistors serving to provide said first signal; said indicating means includes a first indicator connected to said first transistor and a second indicator connected to said second transistor, both said first and second indicators being operable to indicate the proper exposure when both said first and second transistors are non-conductive, either one of said first or second indicators being operable to indicate an improper exposure when either one of said first or second transistors is non-conductive; and said rendering means includes first and second voltage dividers and third and fourth transistors, said first voltage divider and said third transistor being connected to said first transistor and said first indicator, said second voltage divider and said fourth transistor being connected to said second transistor and said second indicator, whereby the inoperativeness of both said indicators indicates that said source voltage is lower than the minimum usable voltage level. 6 An exposure meter comprising: an electric power source; exposure detecting means connected with said electric power source and including a photoelectric element for receiving light from an object to be photographed, means connected with said photoelectric element to introduce exposuRe influencing factors thereinto, and means connected with said photoelectric element and with said introducing means to produce a proper exposure signal when the intensity of the light from the object and the exposure influencing factors provide a proper exposure; indicating means for indicating a proper exposure in response to said proper exposure signal; means (R8, R9; R12, R13; R20, R21) connected to said electric power source for detecting the voltage of said power source, said voltage detecting means producing a voltage signal when the source voltage is higher than the minimum usable voltage of the power source; and control means (T5, T6; T8, T9; T11, T12) having two input terminals, one of which (base of T11) is connected to said exposure detecting means and the other of which (base of T12) is connected to said voltage detecting means, and an output terminal (collector of T12) connected to said indicating means for controlling said indicating means, said control means rendering said indicating means operative to indicate a proper exposure only when said control means receives both of said proper exposure signal and said voltage signal.

Claim 9

An exposure meter according to claim 6, wherein said signal producing means of said exposure detecting means comprises first and second signal producing means, said first signal producing means producing a first exposure signal when the combination of said light intensity and said exposure influencing factors correspond to a proper exposure or an under-exposure, said second signal producing means producing a second exposure signal when said combination corresponds to a proper exposure or an over-exposure; wherein said indicating means comprises first and second indicators; wherein said voltage detecting means comprises first and second voltage detecting means; and wherein said control means comprises first and second control means, said first control means having two input terminals, one of which is connected to said first voltage detecting means and the other of which is connected to said first signal producing means and having an output terminal connected to said first indicator, said second control means having two input terminals, one of which is connected to said second voltage detecting means and the other of which is connected to said second signal producing means and having an output terminal connected to said second indicator, said first control means rendering said first indicator operative only when said first control means receives both of said first exposure signal and said voltage signal, said second control means rendering said second indicator operative only when said second control means receives both of said second exposure signal and said voltage signal, whereby the operation of said first indicator alone indicates an under-exposure, the operation of said second indicator alone indicates an over-exposure, the operation of both said indicators indicates a proper exposure, and the inoperativeness of both said indicators indicates that said source voltage is lower than the minimum usable voltage level.

Claim 10

An exposure meter comprising: an electric power source; exposure detecting means connected to said power source and including a photoelectric element for receiving light from an object to be photographed, means connected with said photoelectric element to introduce exposure influencing factors thereinto, and means connected with said photoelectric element and with said introducing means to produce a proper exposure signal when the combination of the intensity of the light from the object and the exposure influencing factors provides a proper exposure, an over-exposure signal when the combination provides an over-exposure and an under-exposure signal when the combination provides an under-exposure; indicating means operable to indicate a proper exposure, an under-exposure and an over-exposure in response to said proper exposure signal, said under-exposure signal and sAid over-exposure signal, respectively; means connected to said electric power source for detecting the voltage of said power source, said voltage detecting means producing a first voltage signal when the voltage of said power source is higher than the minimum usable voltage of said power source and a second voltage signal when the voltage of said power source is below said minimum usable voltage; and control means having an output terminal connected to said indicating means for controlling said indicating means and having two input terminals, one of which is connected to said exposure detecting means and the other of which is connected to said voltage detecting means, said control means rendering said indicating means operative to indicate a proper exposure when said control means receives both said proper exposure signal and said first voltage signal, to indicate an under-exposure when said control means receives both said under-exposure signal and said first voltage signal, and to indicate an over-exposure when said control means receives both said over-exposure signal and said first voltage signal, whereby when said control means receives said second voltage signal said indicating means is rendered inoperative to indicate that said source voltage is below the minimum usable voltage level.

Claim 11

An exposure meter comprising: an electric power source; exposure detecting means connected to said power source and including a photoelectric element for receiving light from an object to be photographed, means connected with said photoelectric element to introduce exposure influencing factors thereinto, and means connected with said photoelectric element and with said introducing means to produce a proper exposure signal when the combination of the intensity of the light from the object and the exposure influencing factors provides a proper exposure, an over-exposure signal when the combination provides an over-exposure and an under-exposure signal when the combination provides an under-exposure; indicating means operable to indicate a proper exposure, an under-exposure and an over-exposure in response to said proper exposure signal, said under-exposure signal and sAid over-exposure signal, respectively; means connected to said electric power source for detecting the voltage of said power source, said voltage detecting means producing a first voltage signal when the voltage of said power source is higher than the minimum usable voltage of said power source and a second voltage signal when the voltage of said power source is below said minimum usable voltage; and control means having an output terminal connected to said indicating means for controlling said indicating means and having two input terminals, one of which is connected to said exposure detecting means and the other of which is connected to said voltage detecting means, said control means rendering said indicating means operative to indicate a proper exposure when said control means receives both said proper exposure signal and said first voltage signal, to indicate an under-exposure when said control means receives both said under-exposure signal and said first voltage signal, and to indicate an over-exposure when said control means receives both said over-exposure signal and said first voltage signal, whereby when said control means receives said second voltage signal said indicating means is rendered inoperative to indicate that said source voltage is below the minimum usable voltage level.