US3678826A
Expired / Lapsed
US
⏱️ 0.0 years remaining
System for controlling a camera shutter
Assignee: Pentax Corp
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Filing: 1971-06-10
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Granted: 1972-07-25
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Expires: 1991-06-10
Abstract
Abstract A system for controlling a shutter of a single lens reflex camera of the type which measures light which has first passed through the camera objective. A photosensitive unit which has a constant current characteristic is provided for measuring light from the object which has passed through the objective. The photoelectric current of this unit provides for a control transistor a collector current which is substantially equal to the photoelectric current, so that the control transistor will have a base-emitter voltage corresponding to the collector current and thus to the intensity of the light received by the photosensitive unit. This base-emitter voltage is then used in the subsequent determination of an exposure. A holding circuit is provided for maintaining the base-emitter voltage of the control transistor, and an amplifier is electrically connected with the holding circuit and forms with the latter and with the transistor and photosensitive unit a closed loop automatic control circuit.
Inventors
- 👤 Chiharu Mori
- 👤 Katsumi Ota
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-24 07:19
CPC Classifications
G; G03; G03B; G03B7/00; G03B7/08; G03B7/081; G03B7/083
Claims Analysis
Total Claims: 9
Claim 1
Independent Claim
172 words
In a system for the automatic electrical control of the shutter of a single-lens reflex camera of the type which measures light which has first passed through the objective of the camera, photosensitive means for receiving light which has passed through the objective from the object to be photographed and for providing a photoelectric current according to the light received from the object, said photosensitive means having a constant current characteristic, transistor means electrically connected with said photosensitive means for receiving therefrom a collector current substantially equal to said photoelectric current, said transistor means having a base-emitter voltage corresponding to said collector current and serving as part of an input to further circuitry for determining the operation of the camera shutter, holding circuit means electrically connected with said transistor means for holding said base-emitter voltage thereof and amplifier means electrically connected between said photosensitive means and said holding circuit means and forming with said photosensitive means, transistor means, and holding circuit means at least part of a closed loop automatic control circuit.
Claim 2
Dependent Claim
172 words
In a system for the automatic electrical control of the shutter of a single-lens reflex camera of the type which measures light which has first passed through the objective of the camera, photosensitive means for receiving light which has passed through the objective from the object to be photographed and for providing a photoelectric current according to the light received from the object, said photosensitive means having a constant current characteristic, transistor means electrically connected with said photosensitive means for receiving therefrom a collector current substantially equal to said photoelectric current, said transistor means having a base-emitter voltage corresponding to said collector current and serving as part of an input to further circuitry for determining the operation of the camera shutter, holding circuit means electrically connected with said transistor means for holding said base-emitter voltage thereof and amplifier means electrically connected between said photosensitive means and said holding circuit means and forming with said photosensitive means, transistor means, and holding circuit means at least part of a closed loop automatic control circuit.
Claim 3
Dependent Claim
87 words
The combination of claim 1 and wherein an error-detecting resistance means and bias voltage source therefor are connected in series with each other and with said photosensitive means, so that part of the photoelectric current flows through said error-detecting resistance means while the remainder of said photoelectric current is received by said transistor means as the collector current thereof, and said error-detecting resistance means together with the part of the photoelectric current flowing therethrough forming for said amplifier means an input which is approximately equal to zero.
Claim 4
Dependent Claim
30 words
The combination of claim 2 and wherein said error-detecting resistance means is part of said closed loop automatic control circuit and is in the form of a cadmium sulfide photocell.
Claim 5
Dependent Claim
15 words
The combination of claim 2 and wherein said amplifier means is a high gain amplifier.
Claim 6
Dependent Claim
76 words
The combination of claim 1 and wherein said holding circuit means includes a storage capacitor and field effect transistor connected electrically with said transistor means, and switch means for connecting said holding circuit means to said amplifier means only during an initial light-measuring part of an exposure cycle, and for then disconnecting said holding circuit means from said amplifier means so that said holding circuit means will then maintain said base-emitter voltage of said transistor means.
Claim 7
Dependent Claim
98 words
The combination of claim 5 and wherein the camera has a mirror which reflects light to the photosensitive means only during an initial light-measuring part of an exposure operation while said mirror moves out of the path of light passing through the objective just prior to opening of the camera shutter to make an exposure, and shutter-operating means operatively connected with said switch means for displacing the latter to an open position disconnecting said holding circuit means from said amplifier means just prior to swinging of said mirror to a position preventing light from reaching said photosensitive means.
Claim 8
Dependent Claim
22 words
The combination of claim 1 and wherein said photosensitive means is in the form of a photodiode and a transistor connected thereto.
Claim 9
Dependent Claim
30 words
The combination of claim 7 and wherein said photodiode is connected between the collector and base of said transistor of said photosensitive means so as to be inversely biased thereby.
References Cited (Backward Citations)
US3458770A
Cited
US3602717A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1975-07-25 | 1976-01-24 | 1976-07-25 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1979-07-25 | 1980-01-24 | 1980-07-25 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1983-07-25 | 1984-01-24 | 1984-07-25 | $7700.00 | Window Closed / Lapsed |