US3650189A

US3650189A - Low energy level electronic flash modulator

Info

Publication number: US3650189A
Application number: US880795A
Authority: US
Inventors: Conrad H Biber
Original assignee: Polaroid Corp
Current assignee: Polaroid Corp
Priority date: 1969-11-28
Filing date: 1969-11-28
Publication date: 1972-03-21
Anticipated expiration: 1989-03-21

Abstract

A device is provided for modulating actinic radiation emanating from a gas discharge lamp in response to the focus setting of a camera. Plural energy storage sources are provided with one such source having relatively low storage capacity and storing energy of sufficiently high potential to fire the lamp in response to a trigger signal. Another source, having a relatively high capacity for storing energy of a potential sufficient to maintain a discharge from said lamp, but insufficient for initiating such discharge with an acceptable frequency of success, is provided.

Description

United States Patent Biber [451 Mar. 21, 1972 54] LOW ENERGY LEVEL ELECTRONIC 3,353,062 11/1967 Nuckolls ..315 232 x FLASH MODULATOR 2,724,792 11/1955 Nessel ..31s 23s x [72] Inventor: Conrad 11. Biber, Needham, Mass. Primary Examiner samuel Matthews [73] Assignee: v Polaroid Corporation, Cambridge, Mass. Ass sta t Examiner-Michael L. Gellner Filed: Nov. 1969 Attorney-Brown & Mlkulka [21] Appl. No.: 880,795 [57] ABSTRACT A device is provided for modulating actinic radiation emanat- [52] US. Cl. ..95/1 1.5 R, 315/241 P ing from a gas discharge lamp in response to the focus setting [51 Int. Cl. ..G03b 9/70 of a camera. [58] Field ofSearch ..95/l 1.5 R; 315/241 P, 100$,

315/232, 238 Plural energy storage sources are provided with one such source having relatively low storage capacity and storing ener- 56] R f en e Cited gy of sufficiently high potential to fire the lamp in response to a trigger signal. UNITED STATES PATENTS Another source, having a relatively high capacity for storing 2,756,365 7/1956 Germeshausen ..315/238 X energy of a potential sufficient to maintain a discharge from 2,901,671 8/1959 Most ..95/11.5 X said lamp, but i ffi i t f initiating Such discharge with an Engelsmann et al X acceptable frequency of success is provided 3,350,604 10/1967 Erickson ....3 15/241 P 2,721,959 10/1955 Nessel .;....315/238 X 10 Claims, 1 Drawing Figure 1 CAMERA iSHUTTERi i FOCUS 5 :ACTUATOR: CONTROL 1 r .i L

l i 1 23 l l 7 i fi C. 31

I u- 7 i 4| STABILIZED 21 01:. 1,2 POWER L, 1 SUPPLY PATENTEDHARZI I972 INVENTOR. CONRAD H. B l BER ATTORNEYS LOW ENERGY LEVEL ELECTRONIC FLASH MODULATOR BACKGROUND OF THE INVENTION This invention relates, generally, to gas discharge lamp control networks and, more particularly, to an improved means for modulating the actinic radiation emanating from such a lamp.

Many gas discharge lamp control circuits have been developed in recent years to produce flashes of different intensities, or durations, for different exposure situations. These circuits eliminate the problems inherent in adjusting camera controls to provide a proper exposure with a constant light source, such as is commonly provided by more conventional lamp systems.

In one prior art system, a capacitor is connected across the gas discharge lamp and serially connected to a power supply through a variable resistor controlled switch. The resistor is operably connected to the focus control of a camera so that changes in exposure setting will effect a change in the impedance of the resistor, the potential to which the capacitor may be charged and, consequently, theintensity of the lamp output.

In another type of prior art system, an electronic switching network shunts the lamp and receives activating signals from a conventionaltiming network. After a predetermined time, following the firing of the lamp, the timing network activates the switching network to short circuit the lamp and terminate its discharge.

Systems of the above-described prior art types are limited to providing actinic radiation of relatively high intensity because the capacitor connected across the gas discharge lamp, and providing the discharge energy thereto, must be charged to a potential sufficient to fire said lamp with a desired frequency of success.

SUMMARY OF THE INVENTION The subject invention, unlike prior art systems, provides a means for modulating the actinic discharge from a gas discharge lamp while sustaining such discharge with an input potential generally insufficient for initiating said discharge with an acceptable frequency of success. Thus, modulation of a relatively low intensity actinic discharge may be effected.

The foregoing is accomplished by connecting a small capacitor across a gas discharge lamp and charging such capacitor to a potential sufficient to fire said lamp in response to a trigger signal.

A much larger capacitor is connected across the lamp through a diode, which prevents the potential across the small capacitor from being reflected across the larger one.

The signal to the larger capacitor is supplied from the same high potential source as the small capacitor, but is reduced in potential by a variable voltage divider network, the impedance ratio of which is controlled by the focus control of a camera.

A switch, activated by the shutter actuator of the camera, provides a triggering pulse to the lamp (via an electronic switching network) causing the lamp to fire and the small capacitor to discharge therethrough.

The discharge through the lamp is maintained by the larger capacitor at a relatively low intensity controlled by the variable voltage divider network and, hence, the setting of the camera focus control.

Accordingly, it is an object of this invention to provide a means for modulating a relatively low intensity actinic discharge from a gas discharge lamp.

Another object of the instant invention is to initiate an actinic discharge in a gas discharge lamp with a signal of high potential and sustain such discharge with a signal of lower potential.

Still another object of the present invention is to initiate an actinic discharge in a gas discharge lamp with a signal of high potential and sustain such discharge with a signal of lower potential while modulating the intensity of such discharge in response to the focus setting of a camera.

Other objects and many of the attendant advantages of the present invention will be better appreciated and said invention will become clearly understood by reference to the following detailed description when considered in conjunction with the accompanying drawing, illustrating one embodiment of the instant invention, wherein the FIGURE provides a simplified schematic of the invention.

DETAILED DESCRIPTION OF THE INVENTION Referring to the drawing in more detail, a camera, having a shutter actuator and a focus control, is shown generally at l. The camera is operably associated with a gas discharge lamp control network 3, in a manner to be more fully described hereinafter.

The control network 3 includes a stabilized DC power supply 5, such as is common in the art, one side of the output of which is grounded. A pair of resistors 7 and 9, respectively, are serially connected across the output of the power supply 5 to effect a voltage divider network.

Connected across the resistors 7 and 9 is a variable voltage divider network comprising a resistor 11 serially connected with a variable resistor 13.

A gas discharge lamp 15 is connected across the output of the power supply 5 as is a capacitor 17. Another capacitor 19, of substantially greater capacity than said capacitor 17, is connected across the resistor 11 and a diode 21 is connected between the grounded side of the lamp l5 and the common junction of the resistors 11 and 13 and the capacitor 19, with the diodes forward direction being away from ground.

A pair of resistors 23 and 25, respectively, are serially connected with each other so as to form a third voltage divider network which in turn is connected across the capacitor 17.

A triggering transformer 27 is connected with its secondary winding 29 between the trigger electrode 31- (of the lamp 15) and ground and its primary winding 33 serially connected with a capacitor 35 across the resistor 25.

A silicon controlled rectifier 37 is connected at its anode to the junction of the resistors 23 and 25, and with its cathode grounded, so as to shunt the resistor 25 in its conducting state.

The gate of the silicon controlled rectifier is grounded through a resistor 39 to prevent inadvertant triggering of said rectifier 39 by circuit transients.

One side of a single pole-single throw switch 41 is connected to the junction of the resistors 7 and 9 and the other side of the switch 41 is connected through a capacitor 43 to the gate of the silicon controlled rectifier 37.

The shutter actuator of the camera 1 is connected to the switch 41 so that the switch 41 will close when the camera shutter is actuated. The focus control of said camera 1 is connected to the variable resistor 13 in a well-known manner, whereby focusing the camera 1 will change the impedance of the resistor 13 (an amount sufficient to effect a predetermined potential across the capacitor 19) so that the output of the lamp 15 will be made to suit the focus setting.

With the network 3 operably connected to the camera 1, the switch 41 will remain open until the shutter of the camera 1 is actuated. Prior to such time, the capacitor 17 will be charged to the full output potential of the power supply 5 and the capacitor 19 will be charged to a lower potential which will be predetermined by the focus setting of the camera 1. In a like manner, the capacitor 35 will be charged to a potential fixed by the ratio of the resistors 23 and 25 and the output of the power supply 5.

When the shutter of the camera 1 is actuated the switch 41 will close, sending a signal through the capacitor 43, to the gate of the silicon controlled rectifier 37, to effectively turn on said rectifier 37. The resistor 25 will effectively be short circuited by the silicon controlled rectifier 37, permitting the capacitor 35 to discharge rapidly and send a signal through the triggering transformer 27, via the primary winding 33 and the secondary winding 29, to the trigger electrode 31 of the lamp 15.

The signal to the electrode 31 will initiate an actinic discharge through the lamp 15, quickly dissipating the charge stored in the small capacitor 17.

Once the discharge has been started a lower potential will be able to maintain a discharge (of lower intensity) even though such lower potential would not have been sufficient to initiate such a discharge, at least with an acceptable frequency of success. The capacitor 19, with its much greater storage capacity (though lower potential) than the capacitor 17, will provide the necessary energy to maintain the actinic discharge.

it should be noted that the termacceptable frequency of success" has been used herein because a discharge may be initiated over a wide range of potentials.

For example, a potential which is not normally sufficient to initiate a discharge in a gas discharge lamp may, nevertheless, occasionally initiate such a discharge. Thus, the question of frequency of success in effecting such a discharge becomes important. However, success 100 percent of the time is often what is desired.

Consider, now, the case where the parameters of the control network 3 are such that a potential of 500 volts across the lamp will insure the initiation of a discharge therewithin. However, let us assume that the camera 1 is to be provided with three discrete focus settings and is to operate in an environment wherein the intensity of the actinic discharge from the lamp 15 is to be varied with focus setting.

Let us further assume that the potentials across the lamp 15 corresponding to the three focus settings are 360 volts, 180 volts, and 90 volts, respectively. For a particular gas discharge lamp, a potential thereacross of 360volts may be sufficient to insure the initiation of a discharge therein lOO'percent of the time. A potential of I80 volts may insure a discharge with a much lower frequency of success and a potential of 90 volts may be virtually insufficient to initiate a discharge.

Obviously, anything less than 100 percent success in effecting a discharge from the lamp 15 is undesirable for photographic purposes. However, in the example given, a firing potential of 500 volts will be applied across the lamp 15 by the capacitor 17 irrespective of the camera focus setting. Thus, a discharge will be initiated notwithstanding the focus setting and the potential across the capacitor 19 corresponding thereto.

Assuming the potential across the lamp 15 necessary to maintain a discharge therein is below 90 volts, we will be able to effect a discharge at any of the three discrete focus settings and maintain such discharge whether the potential across the capacitor 19 is 360 volts, 180 volts, or 90 volts.

In view of the foregoing, it can readily be seen that many variation and modifications of the present invention are possible and it will be apparent to those skilled in the art that various changes in form and arrangement of components may be made to suit requirements without departing from the spirit and scope of the invention.

It is therefore to be understood that, within the scope of the appended claims, the instant invention may be practised in a manner otherwise than is specifically described herein.

lclaim:

1. In combination with a gas discharge lamp, a device for effecting and modulating actinic radiation therefrom including:

first energy storage means connected to said lamp for supplying energy thereto of sufficient potential to initiate an actinic discharge therein, with a desired frequency of success, in response to a control signal;

second energy storage means for supplying energy to said lamp at a potential insufficient to initiate an actinic discharge therein, with a desired frequency of success,

but sufficient to maintain such a discharge once initiated; said first and second energy storage means being functionally independent; and

means for isolating said second energy storage means from said first energy storage means for preventing the transfer of energy therebetween. 2. The invention as cited in claim 1, additionally including:

means for variably predetermining the potential of the energy stored in said second energy storage means.

3. The invention as set forth in claim 2, further including means for supplying control signals to said lamp for triggering an actinic discharge therein at a predetermined time.

4. The invention of claim 3, further comprising a camera having a focus control and a shutter actuator, with said means for predetermining the potential of the energy in said second energy storage means operably connected to and controlled by said focus control, and said means for supplying triggering control signals to said lamp operably connected to and controlled by said shutter actuator.

5. The invention as recited in claim 4, wherein said first energy storage means shunts said lamp and said second energy storage means is serially connected to said isolation means across said lamp, and wherein current may flow through said isolation means in only one direction.

6. The invention as related in claim 5, wherein said first energy storage means comprises a capacitor and said second energy storage means comprises a capacitor having a higher capacity than that of said first energy storage means.

7. The invention of claim 6, wherein said means for supplying triggering control signals includes:

a transformer having primary and secondary windings;

a capacitor serially connected to the primary of said transformer;

a resistor shunting said capacitor and said primary winding;

means for charging said capacitor; and

means for short circuiting said resistor and responsive to said shutter actuator for generating a triggering control signal in said secondary winding upon activation of said actuator.

8. The invention as related in claim 7, wherein said resistor short circuiting means includes an electronic switching device connected in shunt with said resistor.

9. The invention of claim 8, wherein said electronic switching device comprises a silicon controlled rectifier.

10. In combination with a camera having a shutter actuator and a focus control, an electronic flash modulator, including:

a gas discharge lamp having a trigger electrode;

means connected to said shutter actuator and said trigger electrode for supplying triggering control signals to said trigger electrode in response to activation of said shutter actuator;

first storage means connected across said lamp for supplying electrical energy thereto of sufficient potential to initiate a discharge therein;

second storage means having greater capacity for the storage of electrical energy than said first storage means for supplying electrical energy to said lamp to sustain said discharge for a time interval sufficient to record a photographic image;

means for supplying electrical energy to said first and second storage means, with that supplied to said first storage means having a higher potential than that supplied to said second storage means; and

diode means serially connected between said second storage means and said gas discharge lamp for preventing the transfer of energy between said second storage means and said first storage means.

Claims

1. In combination with a gas discharge lamp, a device for effecting and modulating actinic radiation therefrom including: first energy storage means connected to said lamp for supplying energy thereto of sufficient potential to initiate an actinic discharge therein, with a desired frequency of success, in response to a control signal; second energy storage means for supplying energy to said lamp at a potential insufficient to initiate an actinic discharge therein, with a desired frequency of success, but sufficient to maintain such a discharge once initiated; said first and second energy storage means being functionally independent; and means for isolating said second energy storage means from said first energy storage means for preventing the transfer of energy therebetween.

2. The invention as cited in claim 1, additionally including: means for variably predetermining the potential of the energy stored in said second energy storage means.

7. The invention of claim 6, wherein said means for supplying triggering control signals includes: a transformer having primary and secondary windings; a capacitor serially connected to the primary of said transformer; a resistor shunting said capacitor and said primary winding; means for charging said capacitor; and means for short circuiting said resistor and responsive to said shutter actuator for generating a triggering control signal in said secondary winding upon activation of said actuator.

10. In combination with a camera having a shutter actuator and a focus control, an electronic flash modulator, including: a gas discharge lamp having a trigger electrode; means connected to said shutter actuator and said trigger electrode for supplying triggering control signals to said trigger electrode in response to activation of said shutter actuator; first storage means connected across said lamp for supplying electrical energy thereto of sufficient potential to initiate a discharge therein; second storage means having greater capacity for the storage of electrical energy than said first storage means for supplying electrical energy to said lamp to sustain said discharge for a time interval sufficient to record a photographic image; means for supplying electrical energy to said first and second storage means, with that supplied to said first storage means having a higher potential than that supplied to said second storage means; and diode means serially connected between said second storage means and said gas discharge lamp for preventing the transfer of energy between said second storage means and said first storage means.