US2509967A

US2509967A - Photoflash lamp circuit

Info

Publication number: US2509967A
Application number: US753454A
Authority: US
Inventors: Clinton S Davis
Original assignee: Individual
Current assignee: Individual
Priority date: 1947-06-09
Filing date: 1947-06-09
Publication date: 1950-05-30
Anticipated expiration: 1967-05-30

Description

y 0, 1950 c. s. DAVIS 2,509,967

PHOTOFLASH LAMP CIRCUIT Filed June 9, 1947 k INVENTOR. F 73: 2- BY Clinton Span/ s A z's At tor/veg.

Patented May 30, 1950 PHOTOFLASH LAMP CIRCUIT Clinton S. Davis, Chicago, Ill.

Application June 9, 1947, Serial No. 753,454

1 Claim.

This invention relates to certain new and useful improvements in photoflash lamp circuits and has for its principal object the provision of an improved construction which will be highly efflcient in use and economical in manufacture.

In photographing b the use of photographic flash lamps, it is a common understanding that due to insufiicient illumination photographs do not result in a well defined perspective and lack depth and detail largely because of this insuflicient illumination.

To overcome this objectionable feature it is a common practice to use a master flash lamp to control a slave flash bulb, the latter usually located where the photographer believes necessary for proper illumination. In this employment of a master photographic flash lamp for discharg ing a slave flash bulb, the discharge between the two should be as near simultaneous as it is possible to obtain. In most slave flash bulb circuits with which I am familiar, there is a measurable time lag between the master and the slave flash with the result that the finished photograph is defective due to the lack of proper illumination. It is, therefore, the object of this invention to provide a circuit for a slave photographic flash bulb in which the flash of the slave bulb will be instantaneous with the flash of the master flash lamp and wherein the time lag between the master and slave flash is reduced to a minimum.

Other objects of the invention are the elimination of moving parts, such as relays in the circuit; elimination of filament and filament supply current; and a lower overall current drain.

Other objects will appear hereinafter.

The invention consists in the novel combination and arrangement of parts to be hereinafter described and claimed.

The invention will be best understood by reierence to the accompanying drawings showing the preferred form of construction, and in which:

Fig. 1 is a perspective view of a flash bulb stand having the slave flash bulb control associated therewith; and

Fig. 2 is a circuit diagram for the slave photographic flash bulb.

The several objects of my invention are accom-- plished by the preferred form of construction shown in the accompanying drawings. In Fig. 1, I have fragmentarily illustrated a photographic slave flash bulb assembly. This assembly includes a stand supporting the reflector l l within which is mounted the slave bulb 25. On this stand and mounted thereon in any suitable manner is an enclosure l3 having an opening M to the rear of which is arranged a photo-electric cell [5. The circuit of this photo-electric cell is connected to the slave flash bulb by a conductor it including the lines 24.

In Fig. 2 I have illustrated the circuit diagram. In this circuit diagram the power source is indicated at H, and in this power source is a switch [8. This source could conveniently be a dry cell battery pack.

The circuit includes a voltage dividing potentiometer l9 and the photo-electric cell l5. 2! is a glow discharge trigger-grid tube and in this grid circuit is a trigger-grid current condenser 22.

An anode current limiting resistor is indicated at 23 and is in parallel with the slave flash bulb 25. An anode voltage limiting resistor is indicated at 26 and includes an adjustment element 27. Between the

resistors

23 and 26 and connected at one side to one of the power sources I! is an impulse storage condenser 28.

In the normal operation of my device, switch I8 is closed and the voltage dividing potentiometer advanced to apply a potential such that a discharge takes place between the trigger-grid 2| and cathode. Sufflcient current flows to the trigger-grid current condenser 22 to assure that a breakdown occurs between the anode and the cathode. This anode-cathode discharge is unable to maintain itself due to the limiting action of the anode voltage limiting resistor and so a pulsing condition is established, its period being determined by the values of the anode voltage limiting resistor and the impulse storage condenser. This pulsing conditioning allows the trigger-gr'id 2i to retain control and if its potential is reduced the periodic cathode-anode discharge stops. Thus it becomes possible and practical-to utilize the trigger tube as an electronic switch and at the same time as a visual indicating device, making it possible for the operator to make the proper circuit adjustment as described. Upon completion of such circuit adjustment the photo-flash bulb 25 will be fired by the energy stored in the impulse storage condenser 28 if there is an increase in the illumination falling on the photo-electric cell I5 such as would occur if a master photo-flash bulb were fired so that its light fell on the photo-cell i5. The photo-flash bulb 25 requires a relatively high current on the order of one ampere of very short duration for ignition. The charge stored in the impulse condenser is capable upon release of causing a high current surge to pass through the igniter filament of the photo-flash bulb.

The characteristic steep front of this surge reduces substantially the time normally required to initiate ignition in the slave photo-flash bulb. This advantage plus the almost instantaneous action of the electronic circuit greatly reduces the lag between master and slave flash over other arrangements in prior art.

A typical characteristic of grid controlled electronic discharge tubes is that of a substantial differential in grid potential existing between that required to initiate discharge and that required to extinguish this discharge. In practice, this appears as back lash and precludes the possibility, generally, of bringing the circuit to optimum sensitivity. In my invention, through the proper choice of competent values with special consideration to the internal resistance of the power source, it is possible to obtain an increase in grid potential immediately the discharge is extinguished. This greatly reduces back lash and permits optimum sensitivity settings to be made with ease.

By the arrangement herein set forth it might be said that the slave circuit has been primed for the flash discharge and that all that remains is for the increase in the illumination upon the photo-cell I to effect the instantaneous flash between the slave bulb and a master bulb.

While .I have illustrated and described the preferred form of construction for carrying my invention into "efiect, this is capable of variation and modification without departing from the spirit of the invention. I, therefore, do not wish to 'be limited to the precise details of construction set forth, but desire to avail myself of such variations and modifications as come within the scope of the appended claim.

Having thus described my invention, what I claim as new and desire to protect by Letters Patent is:

In a slave photo-flash circuit comprising a power line having a control switch, a voltage dividing potentiometer across the power line which includes a variable arm, a glow discharge trigger grid tube with its cathode in circuit with one side of the power line and its grid in circuit with the variable arm of the potentiom eter, a trigger grid condenser across said one side of the power line and said arm, a photo-cell connected across the said arm and the other side of the power line, an anode voltage limiting resistor which includes a variable arm, an anode current limiting resistor having one side in circuit with the plate of said tube and the other side thereof in circuit with the anode voltage limiting resistor, a flash bulb connected across the anode current limiting resistor, the variable arm ofsaid anode voltage limiting resistor being connected to said other side of the power line, and an impulse storage condenser having one side in circuit with said one side of the power line and the other side thereof in circuit with said one side of said anode voltage limiting resistor.

CLINTON S. DAVIS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,269,338 Ed'ger'ton -Jan. 6, 1942 2,331,771 Germes'hausen et a1. Oct. 12, 1943 2,336,633 Parson Dec. 14, 1943 2,411,531 Engelhar'dt 1 Nov. 26, 1946 2,432,084 Blair Dec. 9, 1947