US3678825A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Automatic exposure controls for cameras
Assignee: Pentax Corp
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Filing: 1971-05-19
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Granted: 1972-07-25
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Expires: 1991-05-19
Abstract
Abstract A camera for determining automatically the exposure time during which a shutter of the camera remains open. The camera has external photosensitive units respectively receiving light which is external to the camera objective and which has passed through the camera objective into the interior of the camera. A differential circuit interconnects these photosensitive units for correcting the output of the external unit according to the light received by the internal unit. An oscillator circuit is connected to the external photosensitive unit to be operated thereby, and this oscillator circuit produces pulses with intervals therebetween. Each interval will be determined by the external photosensitive unit as corrected by the internal photosensitive unit and the differential circuit. A pair of electromagnets are provided for respectively opening and closing the camera shutter, and a control circuit is connected between the oscillator circuit and these electromagnets to bring about opening and closing of the shutter in response to one pulse and closing of the shutter in response to the next pulse of the oscillator circuit.
Inventors
- 👤 Tsukumo Nobusawa
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-30 15:26
CPC Classifications
G; G03; G03B; G03B7/00; G03B7/08; G03B7/081; G03B7/083
Claims Analysis
Total Claims: 11
Claim 1
Independent Claim
239 words
In a camera, oscillator circuit means for generating pulse with intervals therebetween when said circuit means is in a state of oscillation, external photosensitive means for receiving the light external to an objective of the camera, said external photosensitive means being electrically connected to said oscillator circuit means for placing the latter in said state of oscillation, internal photosensitive means for receiving light which has passed through the objective of the camera into the interior thereof, differential circuit means electrically connected between said internal and external photosensitive means for correcting the output of said external photosensitive means according to the difference between the light received by said internal and external photosensitive means, so that the state of oscillation of said oscillator circuit means is determined according to the output of said external photosensitive means as corrected by the light received by said internal photosensitive means, electrical shutter-opening means for opening a shutter of the camera to start an exposure, electrical shutter-closing means for closing the shutter of the camera to terminate the exposure, and electrical control means electrically connecting said oscillator circuit means to said shutter-opening means and said shutter-closing means for actuating said shutter-opening means to start an exposure in response to one of said pulses of said oscillator circuit means and for actuating said shutter-closing means to terminate the exposure in response to the next pulse of said oscillator circuit means which follows said one pulse thereof.
Claim 2
Dependent Claim
239 words
In a camera, oscillator circuit means for generating pulse with intervals therebetween when said circuit means is in a state of oscillation, external photosensitive means for receiving the light external to an objective of the camera, said external photosensitive means being electrically connected to said oscillator circuit means for placing the latter in said state of oscillation, internal photosensitive means for receiving light which has passed through the objective of the camera into the interior thereof, differential circuit means electrically connected between said internal and external photosensitive means for correcting the output of said external photosensitive means according to the difference between the light received by said internal and external photosensitive means, so that the state of oscillation of said oscillator circuit means is determined according to the output of said external photosensitive means as corrected by the light received by said internal photosensitive means, electrical shutter-opening means for opening a shutter of the camera to start an exposure, electrical shutter-closing means for closing the shutter of the camera to terminate the exposure, and electrical control means electrically connecting said oscillator circuit means to said shutter-opening means and said shutter-closing means for actuating said shutter-opening means to start an exposure in response to one of said pulses of said oscillator circuit means and for actuating said shutter-closing means to terminate the exposure in response to the next pulse of said oscillator circuit means which follows said one pulse thereof.
Claim 3
Dependent Claim
20 words
The combination of claim 1 and wherein said shutter-opening means and said shutter-closing means respectively include a pair of electromagnets.
Claim 4
Dependent Claim
99 words
The combination of claim 1 and wherein said control means includes a pair of silicon control elements electrically connected to said shutter-opening means and said shutter-closing means, respectively, and initially being in a non-conductive state, and a switch for connecting said oscillator circuit means to the silicon control element connected to said shutter-opening means for rendering the latter silicon control element conductive in response to said one pulse, said control means including a diode connected between said silicon control elements for rendering the silicon control element connected to said shutter-closing means conductive only in response to said next pulse.
Claim 5
Dependent Claim
124 words
The combination of claim 1 and wherein said oscillator circuit means includes a capacitor electrically connected to said external photosensitive means to be charged thereby, and a unijunction transistor electrically connected to said capacitor to be rendered conductive when said capacitor has been charged to a predetermined extent, so that said capacitor then discharges through said transistor to provide a pulse whereupon said transistor again becomes non-conductive and said capacitor is again charged to bring about the next pulse after a given interval, whereby according to the period required for charging of the capacitor to render said transisTor conductive, as determined by the intensity of light received by said external photosensitive means, the pulses will be generated at intervals which determine the exposure time.
Claim 6
Dependent Claim
25 words
The combination of claim 4 and wherein a transistor current control circuit is connected between said external photosensitive means and said capacitor in series therewith.
Claim 7
Dependent Claim
41 words
The combination of claim 1 and wherein said differential circuit means includes a capacitor and a switch having one position connecting said capacitor between said internal and external photosensitive means and another position connecting said capacitor to said oscillator circuit means.
Claim 8
Dependent Claim
37 words
The combination of claim 6 and wherein a high input impedance transistor circuit is connected between said capacitor of said differential circuit means and said oscillator circuit means when said switch is in said other position thereof.
Claim 9
Dependent Claim
39 words
The combination of claim 7 and wherein a transistor current control circuit is connected between said high input impedance transistor circuit and said oscillator circuit means as well as between said oscillator circuit means and said external photosensitive means.
Claim 10
Dependent Claim
134 words
The combination of claim 1 and wherein said shutter-opening means and said shutter-closing means respectively include a pair of electromagnets, said control means including a pair of silicon control elements respectively connected to said electromagnets for actuating the latter when said silicon control elements respectively are rendered conductive, a switch for connecting said oscillator circuit means to the silicon control element connected to the electromagnet of said shutter-opening means for rendering the latter silicon control element conductive in response to said one pulse, and said control means including a diode connected between said silicon control elements for rendering the silicon control element connected to said shutter-closing means conductive only in response to said next pulse, whereby the interval between said pulses determines the interval between actuation of said shutter-opening means and said shutter-closing means.
Claim 11
Dependent Claim
107 words
The combination of claim 9 and wherein said oscillator circuit means includes a unijunction transistor having an output connected through said switch to said silicon control element which is connected to said shutter-opening means for transmitting said one pulse to the latter silicon control element, said oscillator circuit means also including a capacitor operatively connected to said unijunction transistor and to said external photosensitive means for providing with said unijunction transistor said pulses with an interval therebetween determined by the intensity of light received by said external photosensitive means as corrected by the intensity of light received by said internal photosensitive means and said differential circuit means.
References Cited (Backward Citations)
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 |