US4051490A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Photographic exposure meter circuit having temperature compensation
Assignee: Pentax Corp
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Filing: 1976-11-10
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Granted: 1977-09-27
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Expires: 1996-11-10
Abstract
Abstract An exposure meter circuit includes a photo diode 2 and associated components 1, 3-6 for producing a first logarithmically compressed voltage V 1 proportional to the apex value B v of the sensed brightness level. The temperature characteristic of the transistor 1 coupled to the diode 2 is compensated for by developing a second logarithmically compressed voltage V 2 and subtracting V 1 from it in an operational amplifier 9. The voltage V 2 is produced by a transistor 11 whose base is coupled to the cathode of a light emitting diode 13 and whose collector output is returned to the power supply through a diode wired transistor 12. The temperature characteristic of the LED is the same as that of a transistor, whereby compensation is realized.
Inventors
- 👤 Masahiro Kawasaki
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-30 15:08
CPC Classifications
G; G01; G01J; G01J1/00; G01J1/42; G01J1/44; G03; G03B; G03B17/00; G03B17/18; G03B7/00; G03B7/08; G03B7/099
Claims Analysis
Total Claims: 5
Claim 1
Independent Claim
103 words
In a temperature compensating photographic exposure meter circuit including means incorporating a photo sensitive element for producing a first logarithmically compressed voltage proportional to the apex value of the brightness of a photographic object, the improvement characterized by: a. a transistor (11), b. a resistor (10) connected to the emitter of said transistor, c. a light emitting diode (13) having its cathode connected to the base of said transistor, d. means (12) for converting the collector output of said transistor into a second logarithmically compressed voltage, and e. meter indication means responsive to the difference between said first and second logarithmically compressed voltages.
Claim 2
Dependent Claim
103 words
In a temperature compensating photographic exposure meter circuit including means incorporating a photo sensitive element for producing a first logarithmically compressed voltage proportional to the apex value of the brightness of a photographic object, the improvement characterized by: a. a transistor (11), b. a resistor (10) connected to the emitter of said transistor, c. a light emitting diode (13) having its cathode connected to the base of said transistor, d. means (12) for converting the collector output of said transistor into a second logarithmically compressed voltage, and e. meter indication means responsive to the difference between said first and second logarithmically compressed voltages.
Claim 3
Dependent Claim
18 words
An exposure meter circuit as defined in claim 1, wherein said converting means comprises a diode wired transistor.
Claim 4
Dependent Claim
66 words
An exposure meter circuit as defined in claim 1, wherein said meter indication means comprises an operational amplifier (9) and a meter indicator (8), and wherein: a. said first voltage is applied to an inverting input of said amplifier, b. said second voltage is applied to a non-inverting input of said amplifier, and c. said meter indicator is connected in a feedback path of said amplifier.
Claim 5
Dependent Claim
66 words
An exposure meter circuit as defined in claim 2, wherein said meter indication means comprises an operational amplifier (9) and a meter indicator (8), and wherein: a. said first voltage is applied to an inverting input of said amplifier, b. said second voltage is applied to a non-inverting input of said amplifier, and c. said meter indicator is connected in a feedback path of said amplifier.
References Cited (Backward Citations)
US3863263A
Cited
DE2351420A1
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1980-09-26 | 1981-03-28 | 1981-09-27 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1984-09-26 | 1985-03-28 | 1985-09-27 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1988-09-26 | 1989-03-28 | 1989-09-27 | $7700.00 | Window Closed / Lapsed |