MODULATED ELECTRONIC FLASH CONTROL

• US 3,634,725 A
• Filed: 09/28/1967
• Issued: 01/11/1972
• Est. Priority Date: 09/28/1967
• Status: Expired due to Term

• Current Assignee: Conrad H. Biber
• Original Assignee: Conrad H. Biber
• Inventors: Biber, Conrad H.
• Primary Examiner(s): Huckert, John W.
• Assistant Examiner(s): Larkins, William D.
• Application Number:
  US04/671,413
• Time in Patent Office: 1,566 Days
• Field of Search: 315/209,29CD,224,238,122,125,126,240,245,293,310,241,241S,241P 340/331,332,366,378 95/11.5R
• US Class Current: 315/241.00P
• CPC Class Codes: G03B 15/05 Combinations of cameras with electronic flash apparatus; Electronic flash units
• CPC Class Codes: G03B 2215/05 Combinations of cameras with electronic flash units
• CPC Class Codes: G03B 7/16 in accordance with both the intensity of the flash source and the distance of the flash source from the object, e.g. in accordance with the "guide number" of the flash bulb and the focusing of the camera
• CPC Class Codes: H05B 41/32 for single flash operation

Abstract

This specification discloses a photoflash circuit for modulating the flash output of a photoflash device in accordance with the focus setting of a camera. The circuit includes an energy storage device, a triggering circuit to supply the energy to the photoflash device and an energy dissipating resistor in series with the flash tube to limit its light output. The circuit includes a control means comprising an electronic switching means to shunt the energy dissipating resistor out of the photoflash device circuit to increase the light output from the flash tube and a timing circuit to produce a triggering signal to energize the switching means. The timing circuit includes an adjustable resistor mechanically coupled to the camera focus controls for varying the triggering time of the switching means and the time the resistor remains in the flash tube circuit.

Claims

1. An electronic flash circuit comprising an electric flash device, means for storing electric energy, means for discharging said energy storing means through said electric flash device for producing a transient flash of light in said flash device, means for dissipating a portion of said energy and limiting the intensity of said flash light and control means for disabling said dissipating means from dissipating energy after a delay interval following the start of said flash of light and increasing the intensity of said flash of light.

2. The electronic flash circuit of claim 1 wherein said dissipating means comprises a resistor connected in series with said flash device.

3. The electronic flash circuit of claim 2 wherein said control means comprises means for shunting said resistor after said delay interval thereby disabling said dissipating means.

4. The electronic flash circuit oF claim 3 wherein said control means further comprises a timing circuit for determining said delay interval and wherein said shunting means is an electronic switching device which is triggered to its conducting state in order to shunt said resistor in response to a signal from said timing circuit after said delay interval.

5. The electronic flash circuit of claim 4 wherein said electronic switching device is a silicon-controlled rectifier.

6. The electronic flash circuit of claim 4 wherein said timing circuit includes a unijunction transistor adapted to be triggered after said delay interval in order to apply said signal to said electronic switching device.

7. The electronic flash circuit of claim 4 wherein said timing circuit comprises a capacitor, means for charging said capacitor and means for applying said signal to said electronic switching device when said capacitor has been charged to a predetermined level in order to trigger said electronic switching device into its conducting state.

8. The electronic flash circuit of claim 7 wherein said timing circuit includes means for varying the charging time of said capacitor.

9. The electronic flash circuit of claim 8 wherein said means for varying the charging time of said capacitor comprises a variable resistor and further including a camera having a variable focus setting and operably associated with said variable resistor whereby the resistance of said variable resistor is controlled in accordance with the focus setting of said camera.

10. The electronic flash circuit of claim 7 wherein said means for charging said capacitor comprises a capacitor 19 a voltage control device for regulating the voltage across said last-mentioned capacitor. ii. An electronic flash circuit comprising a flash tube operable to emit a transcient flash of light when triggered, a resistor connected in series with said flash tube, means for applying a voltage across said series connected resistor and flash tube and circuit means operable for selectively triggering said flash tube and shunting said resistor.

12. An electronic flash circuit as recited in claim 11 wherein said circuit means is operable to shunt said resistor a delay interval after the triggering of said flash tube.

13. An electronic flash circuit comprising a storage capacitor, means for charging said storage capacitor, a flash tube operable to generate a transient flash of light in response to the triggering thereof, circuit means including a resistor for connecting said flash tube to said capacitor so as to provide a discharge path therefor, and means for triggering said flash tube and generating a flash by discharging said capacitor through said flash tube, said circuit means connecting said flash tube in series with said resistor in said discharge path for part of the discharge of said capacitor to generate low-intensity light and removing said resistor from said discharge path for the remainder of the discharge of said capacitor through said flash tube to generate high-intensity light with said flash tube.

14. Circuitry for controlling the light output of a flash camera including, in combination:

25 6, an energy storage capacitor adapted to receive a charging current from a source of supply voltage for charging up to a predetermined voltage level, a flash tube connected to said capacitor for receiving energy therefrom to provide a desired maximum light output from the flash tube, and variable impedance means connected in series with said flash tube and in the discharge path of said capacitor for controlling the discharge current through said flash tube and thereby controlling the light output from said flash tube in accordance with a preselected distance between said flash tube and subject.

15. In a timing circuit for a flash camera of the type having an energy storage capacitor connected in parallel with a flash tube for providing a discharge current therethrough for energizing said flash tube, the improvement comPrising a variable impedance means connected in series with said flashtube and adjustable to a value consistent with the desired discharging current through said flashtube and the desired light output thereof.

16. A method for varying the light output of the flash tube of a flash camera which comprises the steps of:

connecting a variable impedance in series with the flash tube to limit the discharge current therethrough, and adjusting the value of said impedance to limit said discharging current through the flash tube to a level which produces a preselected light output of the flash tube in accordance with the distance between flash camera and subject.