US2614409A - Flash lamp firing circuit - Google Patents

Description

Oct. 21, 1952 H. 1.. MALONE El AL FLASH LAMP FIRING CIRCUIT 2 SHEETS-SHEET 1 Filed Aug. 9, 1951 HAROLD L. MALONE ED6A R 5. MAR VIN INVENTOR.

A TTORNE Y3 Oct. 21, 1952 1 MALQNE r AL 2,614,409

FLASH LAMP FIRING CIRCUIT Filed Aug. 9, 1951 2 SHEETS SHEET 2 FIEl.E

14 FLASH HOLDER CIRCUIT EXTENSION UNIT E HAROLD L. MALONE EDGAR 6. MAR VIN IN VEN TOR.

chronizer switch to fire the lamps in timed Patented Oct. 21, 1952 FLASH LAMP FIRING CIRCUIT Harold L. Malone and Edgar S. Marvin, Rochester, N. Y., assignors to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey Application August 9, 1951, Serial No. 241,074

6 Claims.

The present invention relates to a flash holder having a battery-capacitor flash circuit into which one or more extension lamp units may be connected in series with the lamp socket of the holder, and particularly to an extension plug in the flash holder circuit which is normally short-circuited when no extension unit is connected thereto and which automatically connects a trimmer resistor into the flash holder circuit when no extension unit is connected into the circuit, and cuts the trimmer resistor out when an extension unit is connected into the circuit.

Professional and press photographers are flnding it more and more desirable or necessary to use a plurality of flash lamps in photographing a scene, and to fire them all at one time in synchronism with the opening of the shutter. This means that the main flash holder which is normally attached to the camera must contain a power source sufficient to fire a plurality of lamps at one time and must provide means for selectively connecting a plurality of extension units into the main flash circuit of the holder to be ignited by said power source. In addition to the plurality of lamps used, it is quite common for photographers to use a solenoid shutter vtripper which also relies on the power source of the flash holder for its power. It has been found that a compact and suitable power source for this entire load can be derived from a batterycapacitor power pack wherein two 22 /2 volt hearing aid type dry cells are used to charge up an electrolytic capacitor which is then discharged through the lamps upon closure of the synrelation with opening of the shutter.

Because of the fact that power packs of this nature put out a relatively high current momentarily, i. e., 25 amperes in the circuit to be described, some difliculty has been encountered in using flash holders so powered in combination with shutters having a built-in flash switch or synchronizer. It has been found that these high currents tend to melt or pit the relatively light switch contacts used in such built-in synchronizers, and that this condition is aggravated by the fact that the switch contacts in this 'type of synchronizer have a tendency to bounce or vibrate at a high rate of. speed with the result that the circuit is actually made and broken many times during the very-short duration that the high current is flowing. It has also been found that'in order to fire a plurality of lamps simultaneously in a reliable fashion, the lamps should all be connected in series with one another and the power source rather than in parallel relation. When a flash holder is used whose circuit is designed to selectively accommodate one or more extension units, this means that a shorting type extension plug must be used in order that the circuit will function when one or more extension units are not'being used.

Accordingly, the primary object of the present invention is to provide a flash holder which has a battery-capacitor power source which is sufflciently powerful to ignite a plurality of flash lamps at the same time and which permits the selective addition of one or more extension lamp units to its power circuit in series connection without in any way affecting the normal operation of the circuit.

Another object is to provide a flash holder of the type described which includes an extension plug for connecting a built-in flash synchronizer into the circuit in controlling relation therewith.

A further object is to provide a flash holder whose circuit is so designed that the resistance in the circuit is always suflicient, regardless of the number of lamps used, to prevent the output of a current which is so high as to injure the contacts of a built-in flash synchronizer when used in conjunction therewith.

And yet another object is to provide a flash holder whose circuit includes extension plugs which are connected in series with the lamp socket of the holder and which are normally short-circuited so as to leave the flash holder circuit complete when one or more extension plugs are not in use.

And a further object is to provide a flash holder of the type described wherein the extension plugs are designed to automatically cut a trimmer resistorinto, and remove said trimmer resistor from, the .flash circuit as an extension unit is left out .oradded, respectively, to the flash holder circuit.. I

Still another object is to provide an extension plug of the type described for use in a flash circuit which is simple and inexpensive-to manufacture and, at the same time, compact and foolproof in operation.

The novelfeatures that we consider characteristic of our invention are set forth with particularity in the appended claims. Theinvention-itself,- however, both as to its organization and its methods of operation, together with additional objects and advantages thereof, will best be understood from the following description when read in connection with the accompanying drawing in which:

Fig. -1 is a vertical sectional view of one-form of flash holder constructed in accordance with one embodiment of the present invention;

Fig. 21s a circuit diagram of the flash circuit contained in the flash holder and combined with might form a part;

Fig. 4 is a rear elevational view of the exten sion plug shown in Fig. 3; and

Fig. 5 is an enlarged perspective detail of the spring contact of the extension plug removed from the plug in order to show its particular shape.

Referring now to the drawings, and particularly Fig. 1, a flash holder constructed in accordance with the present invention may comprise a generally cylindrical housing in which may be made of any light material, i. e., magnesium, Bakelite, etc., since it is generally mounted on the side of a camera. In the present instance, it will be assumed that the housing is made of magnesium and is electrically conducting so that certain parts of the flash circuit will be described as insulated therefrom. If the housing were made of Bakelite, this extra installation would, of course, not be necessary.

The upper end of the housing is provided with a bore in which a bayonet-type lamp socket H is mounted within an insulating sleeve l2. A conventional flash lamp L is adapted to be placed in this socket and is backed up by a reflector l3 fixed to the housing in encircling relation with the socket. The base contact of the lamp is adapted to engage a metal contact strap 14 fixed to the wall of the housing and insulated therefrom by insulation material 15. That portion of the contact strap [4 engaged by the lamp base is so formed as to be resilient, and thus provide a good electrical contact between the same and the base of the lamp.

Also contained in the housing is the power pack for the flash circuit, said pack comprising a pair of 22 /2 volt hearing aid type dry batteries B and a 150 mfd. electrolytic capacitor C. The batteries and capacitor are connected in series with a 2700 ohm current limiting resistor R connected between them, it being noted that the negative side of the condenser is hooked to the neg ative pole of the batteries since the operation of an electrolytic capacitor depends upon current flowing through the same in one direction only. As indicated, the batteries may be supported on a partition 15" in the housing while the capacitor is located between this partition and the bottom of the housing, and the resistor R extends through a hole in the partition. The positive terminal of the batteries is connected to the contact strap 14 through a lead [5 and the positive side of the capacitor C is connected by lead I! to an extension plug l8 onto which an extension unit E (see Fig. 2) containing an additional flash lamp L may be connected by means of a flash holder plug F. This plug [8 is in turn connected in series with a second extension plug 18 just like it and to which a second extension unit can be connected. This second plug I8 is then connected by lead I9 to the socket l I to complete the flash circuit of the flash holder. As shown, the extension plugs l8 and [8 (which will be described fully hereinafter) include a male type bayonet terminal 25, into which a female type flash holder plug on an extension unit is adapted to engage in a known manner, and which terminal is seated in a recess 20 in the wall of the housing so that the plug is protected against damage resulting from accidental blows.

Looking now at Fig. 2, it will be seen that the batteries B, resistor R, capacitor C, extension plugs 18 and I8 and lamp L are connected in series relation in a closed loop circuit so that just as soon as a new lamp L is placed in the flash holder socket the battery starts to charge the capacitor throughthe current-limiting resistor R. It will be noted that just as soon as the lamps are flashed the charging circuit is broken so that the capacitor will not start to charge again until new lamps are placed in the circuit. This automatically protects the batteries against constant wasteful drain as would be occasioned by long waiting periods between photographic assignments. In order for this circuit to function whether or not there are extension units E connected to the extension plugs l8 and i8, these extension plugs are made so as to be automatically short-circuited when no extension unit is connected thereto as will be fully described hereinafter. Now, in order to flash the lamp L and any extension units connected into the circuit, the capacitor C must be discharged through the lamps. To this end, a synchronizer switch is connected across the capacitor and lamps ahead of the batteries and resistor R. Assuming the synchronizer switch is one built into a shutter having a pair of external terminals to which an extension cord may be connected, the housing 10 is provided with a shutter plug 2| adapted to receive a companion plug on the end of such a cord. As shown in Fig. 1, this shutter plug may be one of the female bayonet type adapted to receive a companion male plug connected to the switch contacts in the shutter. The shell terminal of shutter plug 2| is connected by lead 22 to the lead l6 of the flash circuit, and the center terminal of plug 2| is connected by lead 23 into the flash circuit ahead of resistor R. Now, when the capacitor is charged and the flash switch in the shutter is closed, the capacitor discharges across the lamps and ignites them.

Inasmuch as a power source of this nature is capable of producing a momentary current output as high as 25 amperes, some means must be provided to guard against such a high current being put through built-in shutter contacts lest they be damaged or destroyed. The extension plug which we have designed, and which will-now be described, automatically limits the current flow through the circuit to a safe value and, in addition, automatically becomes short-circuited when no extension unit is connected thereto as is required of the series connection used inthis flash circuit. Referring now to Figs. 3, 4 and 5, each of the extension plugs 18 and I8 comprises a pair of insulating plates and 3 l, of the shape best shown in Fig. 4, spaced apart by a washer 32 of insulating material and held together by rivet 33. Fastened to the face of plate 3| by rivet 33 is a first contact 34, the lower end 35 of which is bowed to form a spring, the lower end of which is normally urged toward the left, looking at Fig. 3. This first contact is of the form best shown in Fig. 5, and its extreme lower end is provided with an elongated slot 36 and a pair of turned-in ears 31.

A bayonet-type male terminal 38 is staked in an aperture in plate 38 in electrical contact with a second contact 39 disposed between the two plates 33 and 31. This contact 39 has one end 40 extending below the plates 30 and 31 and provided with a hole 4! through which lead wires may be inserted to connect the plug into the flash circuit. The other end of contact 39 is turned over as indicated at '42 and xtends into a hole 43 in plate 30 to hold the contact against rotation about terminal 38. slid-ably mounted within an insulating sleeve '44 within terminal 38 is a second terminal 45 which takes the form of a rod. The outer end of this terminal 45 is adapted to engage the center contact of a female bayonet type connector designed to flt on terminal 38 and is enlarged as shown at 45 to limit the inward travel of the rod relative to the sleeve 44. The inner end of rod 45 is provided with a circumferential groove 41 which is embraced by the slotted end 36 of first contact 34. This connection both physically and electrically connects contact 34 to second terminal 45 and the normal spring action of the bowed portion of contact 34 acts to move terminal to its extended position (the solid line position shown in Fig. 3). When the terminal 45 is in this position, as it will be when no extension unit is connected thereto, the cars 31 and the lower end of first contact 34 engage a third contact of the iform best shown in Fig. 4 which is riveted to the inside face of insulating plate 3|.

The lower end of this third contact is electri- Plug is short-circuited this resistor is automatically connected into the flash circuit. The value of this trimmer resistor is chosen so as to limit the value of current flowing through the circuit upon discharge of the capacitor to a safe value and thereby protect the switch contacts of the flash switch built into the shutter. In the present instance, we have found that a 05 ohm resistor across each extension plug serves this purpose satisfactorily.

When an extension unit is connected to the extension plug, the terminal 4-5 is retracted to the dotted line position of Fig. 3 and in which position the cars 31 on the lower end of first contact 34 are moved out of engagement with third contact 50, and the circuit is now from contact 34, to terminal 45, through extension E, to second terminal 38, and thence to second contact 39 and to the line. In this condition, the trimmer resistor 5| is automatically cut out of the circuit by the opening of the switch comprising ears 31 of first contact 34 and third contact 50, and the resistance of the extension unit E is added to the circuit and will serve the same purpose as trimmer resistor 5|, namely to limit the peak current flowing through the shutter switch S upon discharge of the condenser to a safe value. Just as soon as an extension unit is removed from the circuit, the switch formed by contacts 34 and 50 will automatically close to short-circuit the extension plug and connect the trimmer resistor 5| back into the circuit.

In Fig. 3 we have shown a single extension plug I8 connected into a flash circuit having all of the components included in the complete circuit oi the flash holder, as shown in Fig. 2, but arranged in a slightly different manner to emphasize the discharge circuit of the capacitor in which the extension plug functions.

In this figure we have diagrammatically illustrated a shutter-controlled flash switch S in the circuit instead of merely a shutter plug as in Fig. 2 through which such a switch is adapted to be plugged into the circuit. Looking at Fig. 3, when the shutter switch S is closed and no extension unit is connected to extension plug l8, the current from the capacitor C flows through shutter switch S, first contact 34, ears 31, third contact 50, trimmer resistor 5| and lamp L back to C. When an extension unit E is attached to plug ID, the second terminal 45 is shifted to the dotted-line position and ears 31 on contact 34 are moved out of engagement with third contact 50 so that current can't flow through the trimmer resistor 5|. Instead, current now flows from C through shutter switch S, flrst contact 34, terminal 45 through extension unit E to first terminal 38, second contact 39 and lamp Lback to C.

When two extension plugs areused, as show at I8 and i8 in Fig. 1, then they are hooked in series in the flash circuit by connecting the second contact 39 of one with the first contact 34 of the other. If the extension unit E is provided with an extension plug I8", as indicated in Fig. 2, it will be of exactly the same construction as the described extension plugs 3 and I8 and will be'connected in series with the flash holder plug and lamp socket of the extension unit. As a result, when the extension unit E is plugged into the lamp circuit of the flash holder, the extension plug I8 will function in precisely the same manner as plugs |8 and I8 which are a part of the flash holder circuit and will, in fact, become a part of the complete flash circuit wherein all of the components forming a part of the capacitor discharge circuit are connected in series.

Although we have shown and described certain specific embodiments of our invention, we are fully aware that many modifications thereof are possible. Our invention, therefore, is not to be limited to the precise details of construction shown and described by way of disclosure, but is intended to cover all embodiments coming within the scope of the appended claims.

Having thus described our invention, what we claim is new and desire to secure by Letters Patent of the United States is: l

l. A flash holder-comprising in combination a housing, a lamp socket in said holder adapted-to receive a flash lamp, a power pack in said housing for igniting said flash lamp and including a capacitor in series with said socket and a battery for charging said capacitor, an extension plug in the wall of said housing adapted to connect a synchronizer switch in circuit with said socket and capacitor for discharging said capacitor through said socket to ignite the lamp therein, a normally shorted extension plug in the wall of said housing connected in series with said socket and capacitor and adapted to receive a connector for connecting another flashlamp into the circuit of said housing in series with the socket therein, said extension plug including a first, contact of one polarity, a second contact of the other polarity, a third contact insulated from the other two, a trimmer resistor connecting said second and third contacts, a normally closed shorting switch between said first and third contacts which automatically introduces said resistor into the lamp circuit of the housing when no extension unit is connected to said plug, a pair of terminals electrically connected to said first and second contacts, respectively, adapted to physically receive said extension connector and electrically connect the same into the circuit of the flash holder, one of said terminals movably mounted relative to said plug and normally moved to an extended position and adapted to be retracted when said extension connection is applied thereto, and means operatively connecting said movable terminal with said shorting switch whereby said switch is allowed to close when said terminal is in its normal extended position and is opened by movement of said terminal toits retractedposition. a

2. A flash holder comprising in combination a housing, a lamp socket in said holder adapted to receive a flash lamp, a power pack in said housing for igniting said flash lamp, and including a capacitor, a battery and a limiting resistor connected in series with each other and said socket whereby said capacitor is charged only when a lamp is placed in said socket, a synchronizing switch in parallel with said capacitor and lamp socket to discharge said capacitor through said socket and ignite the lamp, an extension plug connected in series with said lamp socket and in that part of the circuit through which the capacitor is discharged and adapted to receive a connector for connecting another flash lamp into the lamp circuit in series with the socket of the holder, said extension plug including a contact of one polarity, a second contact of the other polarity, a third contact insulated from the other two contacts, a trimmer resistor electrically connected between said second and third contacts, a;normally closed switch between said first and third contacts, a pair of terminals electrically connected to said first and second contacts, respectively, adapted to physically receive said extension connector and electrically connect the same into the circuit of said flash holder, one of said terminals movably mounted relative to said plug and connected to said switch so as to open the same when the extension connector is attached thereto, whereby when said extension is connected into the circuit said trimmer resistor is cut out of the circuit.

3. A flash holder comprising in combination a housing, a lamp socket in said holder adapted connected in series with said lamp socket and in that part of thecircuit through which the capacitor is discharged and adapted to receive a connector for connecting another flash lamp into the lamp circuit of the flash holder, said extension plug including a contact of one polarity,

a second contact of the other polarity, a third contact insulated from the other two contacts, a trimmer resistor electrically connected between said second and third contacts, a normally closed switch between said first and third contacts, a pair of terminals electrically connected to. said first and second contacts, respectively, adapted to physically receive said extension connector and electrically connect the same into the circuit of said flash holder, one of said terminals movably mounted relative to said plug and connected to said switch so as to open the same when the extension connector is attachedthereto, whereby when said extension is connected into the circuit said trimmer resistor is-cut out of the circuit.

An extension plug for selectively connecting an additional flash lamp into a fiash circuit including a flash larnp socket,- a capacitor and a synchronizing switch connected in series so that closing of said switch discharges said capacitor to flash the lamps, and comprising a first contact and a second contact connected in said circuit in series relation with said lamp socket and capacitor, a third contact insulated from the other two, a trimmer resistor connected between said second and third contacts, a pair otter-minals adapted to be physically and electrically connected to an extension connector wired to an auxiliary flash lamp socket, one of said terminals being stationary and electrically connected to said second contact, the other terminal being electrically connected to said first contact and movable between a normally extended position and a retracted position and adapted to be moved to its retracted position when said extension connector is physically connected thereto, a normally closed switch between said first and third contacts which short circuits said plug with said trimmer resistor in the circuit, and means for connecting said movable terminal to saidswitch to open said switch when the movable terminal is moved to its retracted position, whereby the trimmer resistor is disconnected from the circuit when an auxiliary flash lamp is added thereto.

5. An extension plug according to -claim- ,4 characterized by the fact that said normally closed switch comprises a portion of said first contact deformed to provide a spring arm, the

end of which is normally urged into engagement with said third contact, the end of said arm positively connected to said movable terminal so that the spring tensiontherein serves to move said terminal to its extended position and retraction of the terminal moves the end of the arm from engagement with the third contact.

6. An extension plug forselectively connecting an additional flash lamp into a flash circuit including a flash lamp socket, a capacitor and a synchronizing switch connected in series so that closing of said switch discharges said capacitor to flash the lamps, and comprising a first contact and a second contact connected in said circuit in series relation with said lamp socket and capacitor, a third contact insulated .from the other two, a trimmer resistor connected between said second and third contacts, a pair of terminals adapted to be physically and electrically connected to an extension connector wired to an auxiliary flash lamp socket, one of said terminals being stationary and electrically connected to said second contact, the other terminal being a plunger mounted to slide from a normally-extended position to a retracted position when said extension connector is attached thereto and having a circumferential groove adjacent its inner end, a portion of said first contact deformed extended position and retraction of said plunger moves the end of said arm out of engagement with said third contact.

HAROLD L. MALONE. EDGAR S. NLARVIN.

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

UNITED STATES PATENTS Number Name Date 2,553,662 Marsal May 22; 1951 2,584,858

Dritz Feb. 5, 1952

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