Exposure warning circuit for photographic cameras

Claim 2

An exposure warning circuit for photographic cameras comprising: at least one exposure-warning indicating means, at least one pulse-width comparison circuit having two input terminals connected to said exposure-warning indicating means, an exposure pulse generating circuit connected to one of the input terminals of said pulse-width comparison circuit and generating an exposure pulse with a pulse width in inverse proportion to the light intensity of the object, and at least one reference pulse generating circuit connected to the other input terminal of said pulse width comparison circuit and generating a reference pulse of pre-determined pulse width relative to the exposure time to be warned; said exposure warning circuit controls the operation of said exposure-warning indicating means by making a comparison between pulse widths of said exposure pulse and reference pulse.

Claim 3

An exposure warning circuit for photographic cameras according to claim 1, in which said exposure-warning indicating means is a lamp.

Claim 4

An exposure warning circuit for photographic cameras according to claim 1, in which said pulse-width comparison circuit comprises a pair of transistors respectively having a base connected to the collector of the other transistor in the pair and another pair of transistors having collectors respectively connected to respective emitters of aforesaid pair of transistors.

Claim 5

An exposure warning circuit for photographic cameras according to claim 1, in which said exposure pulse generating circuit comprises a photoconductive element and capacitors connectable in series to said photoconductive element.

Claim 6

An exposure warning circuit for photographic cameras according to claim 1, in which said reference pulse generating circuit is arranged by a mono-stable multi-vibrator comprising transistors.

Claim 7

An exposure warning circuit for photographic cameras according to claim 1, in which said reference pulse generating circuit is arranged to generate a pulse of a width to warn over-exposure.

Claim 8

An exposure warning circuit for photographic cameras according to claim 1, in which said reference pulse generating circuit is arranged to generate a pulse of a width to indicate high-speed exposure.

Claim 9

An exposure warning circuit for photographic cameras according to claim 1, in which said reference pulse generating circuit is arranged to generate a pulse of a width to indicate middle-speed exposure.

Claim 10

An exposure warning circuit for photographic cameras according to claim 1, in which said reference pulse generating circuit is arranged to generate a pulse of a width to indicate low-speed exposure.

Claim 11

An exposure warning circuit for photographic cameras according to claim 1, in which said reference pulse generating circuit is arranged to generate a pulse of a width to warn under-exposure.

Claim 12

An exposure warning circuit for photographic cameras according to claim 1, in which pulse widths of said exposure pulse and said reference pulse are respectively condensed to 1/500.

Claim 13

An exposure warning circuit for photographic cameras comprising: an over-exposure warning lamp, a first pulse-width comparison circuit having two input terminals connected to said over-exposure warning lamp, a first reference pulse generating circuit connected to one of the input terminals of said first pulse-width comparison circuit and generating a reference pulse for over-exposure warning, a high-speed exposure indicating lamp whose one terminal is connected to said over-exposure warning lamp, a second pulse-width comparison circuit having two input terminals and having an output terminal connected to another terminal of said high-speed exposure indicating lamp, a second reference pulse generating circuit connected to one of the input terminals of said second pulse-width comparison circuit and generating a reference pulse for high-speed exposure indication, an exposure pulse generating circuit having an output terminal connected commonly to other input terminals of said first and second pulse width comparison circuit and generating an exposure pulse of a width in inverse proportion to the light intensity of the object to be photographed, and a diode inserted between output terminals of said first and second pulse-width comparison circuits, said exposure warning circuit is arranged to light only one of said over-exposure warning lamp and said high-speed exposure indicating lamp by making a comparison between the pulse width of said exposure pulse and pulse widths of respective reference pulses.

Claim 14

An exposure warning circuit for photographic cameras comprising: an over-exposure warning lamp, a first pulse-width comparison circuit having two input terminals connected to said over-exposure warning lamp, a first reference pulse generating circuit connected to one of the input terminals of said first pulse-width comparison circuit and generating a reference pulse for over-exposure warning, a high-speed exposure indicating lamp whose one terminal is connected to said over-exposure warning lamp, a second pulse-width comparison circuit having two input terminals and having an output terminal connected to another terminal of said high-speed exposure indicating lamp, a second reference pulse generating circuit connected to one of the input terminals of said second pulse-width comparison circuit and generating a reference pulse for high-speed exposure indication, an exposure pulse generating circuit having an output terminal connected commonly to other input terminals of said first and second pulse width comparison circuit and generating an exposure pulse of a width in inverse proportion to the light intensity of the object to be photographed, and a diode inserted between output terminals of said first and second pulse-width comparison circuits, said exposure warning circuit is arranged to light only one of said over-exposure warning lamp and said high-speed exposure indicating lamp by making a comparison between the pulse width of said exposure pulse and pulse widths of respective reference pulses.

Claim 15

An exposure warning circuit for photographic cameras according to claim 12, in which said exposure warning circuit further comprises a middle-speed exposure indicating lamp whose one terminal is connected to said high-speed exposure indicating lamp, a third puLse-width comparison circuit whose one input terminal is connected to the output terminal of said exposure pulse generating circuit and whose output terminal is connected to the another terminal of said middle-speed exposure indicating lamp, a third reference pulse generating circuit connected to another terminal of said third pulse-width comparison circuit and generating a reference pulse for middle-speed exposure indication, a diode inserted between output terminals of said first and third pulse-width comparison circuits, and a diode inserted between output terminals of said second and third pulse-width comparison circuit, said exposure warning circuit is arranged to light only one out of said over exposure warning lamp, said high-speed exposure indicating lamp and said middle-speed exposure indicating lamp by making comparison among pulse widths of said exposure pulse and of reference pulses.

Claim 16

An exposure warning circuit for photographic cameras according to claim 13, in which said exposure warning circuit further comprises a low-speed exposure indicating lamp and an under-exposure warning lamp respectively having a terminal connected to said middle-speed exposure indicating lamp, a fourth pulse-width comparison circuit whose one input terminal is connected to the output terminal of said exposure pulse generating circuit and whose one output terminal is connected to another terminal of said low-speed exposure indicating lamp and whose another output terminal connected to another terminal of said under-exposure warning lamp, a fourth reference pulse generating circuit connected to another input terminal of said fourth pulse-width comparison circuit and generating a reference pulse for low-speed exposure indicating pulse, diodes respectively inserted between output terminals of said first and fourth pulse-width comparison circuits, diodes respectively inserted between output terminals of said second and fourth pulse-width comparison circuits, and diodes respectively inserted between output terminals of said third and fourth pulse-width comparison circuits, said exposure warning circuit is arranged to light only one lamp out of said over-exposure warning lamp, said high-speed exposure indicating lamp, said middle-speed exposure indicating lamp, said low-speed exposure indicating lamp and said under-exposure warning lamp by making comparison between pulse widths of said exposure pulse and of each reference pulse.