Patent US3869642A successfully refreshed from Google Patents.
US3869642A
Expired / Lapsed
US
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Control circuit for electronic flash apparatus
Assignee: Rollei Werke Franke und Heidecke GmbH and Co KG
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Filing: 1974-03-27
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Granted: 1975-03-04
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Expires: 1994-03-27
Abstract
Abstract Electronic flash apparatus for photographic purposes, of the type in which light sensitive integrating means receives light reflected from the subject being photographed, and terminates the flash when the reflected light reaches a threshold value. A special circuit is provided for greatly increasing the speed of response to the reflected light, thus enabling the production of a flash of extremely short duration as required in close-up photography. This avoids the overexposure which often occurs with conventional electronic flash apparatus when taking close-up photographs. The control circuit includes a capacitor, a resistor, and an inductance, so dimensioned that the time constant formed from the resistor and the capacitor is equal to the time constant formed by the resistor and the inductance. This enables the response time of the control circuit to be measured in nanoseconds rather than in microseconds.
Inventors
- 👤 Mehmet Sabanci
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-30 04:43
CPC Classifications
H; H05; H05B; H05B41/00; H05B41/14; H05B41/30; H05B41/32; H05B41/325
Claims Analysis
Total Claims: 6
Claim 1
Independent Claim
153 words
Electronic flash apparatus for photographiC illumination comprising flash producing means, flash terminating means including a thyristor effective, upon actuation, to terminate a flash produced by said producing means, said thyristor having a control grid, flash measuring means for measuring an integrated amount of light reflected from an object being photographed, and control circuit means responsive to said measuring means for actuating said thyristor to teminate said flash when the integrated amount of light measured by said measuring means reaches a threshold value, said control circuit means including a capacitor (17) connected to said control grid, and an inductance (18) and a resistor (19) connected in series with each other and in parallel with said capacitor (17), said capacitor, inductance, and resistance being so dimensioned that the time constant resulting from the dimensions of said capacitor and resistor is substantially equal to the time constant resulting from the dimensions of said inductance and resistor.
Claim 2
Dependent Claim
153 words
Electronic flash apparatus for photographiC illumination comprising flash producing means, flash terminating means including a thyristor effective, upon actuation, to terminate a flash produced by said producing means, said thyristor having a control grid, flash measuring means for measuring an integrated amount of light reflected from an object being photographed, and control circuit means responsive to said measuring means for actuating said thyristor to teminate said flash when the integrated amount of light measured by said measuring means reaches a threshold value, said control circuit means including a capacitor (17) connected to said control grid, and an inductance (18) and a resistor (19) connected in series with each other and in parallel with said capacitor (17), said capacitor, inductance, and resistance being so dimensioned that the time constant resulting from the dimensions of said capacitor and resistor is substantially equal to the time constant resulting from the dimensions of said inductance and resistor.
Claim 3
Dependent Claim
71 words
Flash apparatus as defined in claim 1, wherein said flash producing means comprises a flash tube, and wherein said thyristor has an anode and a cathode, further comprising a series circuit having a capacitor, a resistor, and a voltage divider in series with each other, said series circuit being connected in parallel with said flash tube, said cathode of said thyristor being connected to an intermediate tap of said voltage divider.
Claim 4
Dependent Claim
19 words
Flash apparatus as defined in claim 2, further comprising a Zener diode connected in parallel with said voltage divider.
Claim 5
Dependent Claim
29 words
Flash apparatus as defined in claim 2, wherein said measuring means comprises a photo transistor having an emitter, said emitter being connected to said control grid of said thyristor.
Claim 6
Dependent Claim
91 words
Flash apparatus as defined in claim 2, wherein said terminating means comprises a quench tube 4 having an ignition electrode, a transformer (5) having a secondary winding connected to said ignition electrode and also having a primary winding, and a termination capacitor (6) connected to said primary winding and to the anode of said thyristor in such manner that when said thyristor becomes conductive, said termination capacitor (6) may discharge through said primary winding to create a pulse in said secondary winding and said ignition electrode to ignite said quench tube.
References Cited (Backward Citations)
US3809954A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1978-03-03 | 1978-09-02 | 1979-03-04 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1982-03-03 | 1982-09-02 | 1983-03-04 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1986-03-03 | 1986-09-02 | 1987-03-04 | $7700.00 | Window Closed / Lapsed |