US2609523A - Photoflash system - Google Patents

Description

R. A. STEIN ETAL PHOTOFLASH SYSTEM Sept. 2, 1952 Filed June 21,

INVENTOR. WQQ T M Patented Sept. 2, 1!?52 Ohio, assignors to Globe Industries,

ton,"hio, a corporation of Ohio n D w- Application June 21, 1951, Serial No. 233,427 l2 Claims. (01. 3151- 354) In the normal use in indoor photography of photoflood lamps, or high amperage incandescent filament lamps, as a source of illumination, the lamps stay illuminated during the preparatory stages. This reduces the useful life of the lamp and in addition causes considerable annoyance to the subject and to the photographer.

This application is a continuation-in-part of our copending application Serial No. 18,384, filed April 1, 1948, now abandoned, for Photofiash System.

Quiz of the aims of the present invention is to eliminate the full illumination of the lamps dur: ing the preparatory stages.

In addition, the present invention aims to employ the photofiood high amperage incandescent filament lamp in the same manner as flash bulbs.

In other words, the present invention provides asyst'em of indoor photography employing high amperage incandescent filament lamps, known in the trade as photoflood lamps or bulbs at a supernormal illumination with the result that snapshots may be taken with great facility. The supernormal or high luminosity of the lamp is obtained by imposing upon the'filament asuper normal voltage and passing through the filament a supernormal current which brings the filament to peak temperatures which approxi'mate'the melting point of the filament, vtheduration 'of this peak voltage, current and temperature, how"- ever, being so short that the useful life of the bulb .is 'not materially shortened.

the normal operation of the hood light at rated voltage an interval of approximately '100 milliseconds lapses between the "closing of the switch and the' maximum luminosityproduced by the hood light. In the system of the present inventiont'he supernormal luminosity is obtained with ,aftime delay of only abOlit' 20' milliseconds or less." Thi's'd'elaycorresponds .to the conventional time delays in solenoid operated shutter mechanisms of cameras and the present system, therefore can be readily employed to be operated by such mechanisms and when so employed will produce the desired peak luminosity at the desired time in the operation of the shutter."

In the present invention the flood light or tion of the lam maintains the filament at a rela: tively hi h empe u and P m ts the time delay in reaching the supernormal luminosity I peak to be not more than 20 milliseconds.

Another advantage of the present invention t that as compared with the normal use of such lamps in which they remained at their rated luminosity for substantial periods during each exposure lasting into many minutes, by the use of the present invention, the bulb is employed during. the same period at reduced luminosity and at a supernormal luminosity for only a short,- time with the consequent increase of the efiective life of the bulb. I

Other objects and advantages reside in the construction of parts, the combination thereof the mode of operation, as will become more apparent from the iollowing description.

A more detailed understanding of the present invention will be had from 'the'foll'owing spac ng cation and the accompanying drawings which 1 illustrate the preferred embodimentsof the in} vention, it being understood that variationsthereof falling within thescope' of the appended claims will be apparent to persons skilled in the art.

In the drawings, Figure 1 is a diagrammatic" illustration of one'form of the invention; Figure 2 is a diagrammatic illustration of the system shown in Figure 1 associated'wi'th a sale;

noid operated camera shutter."

Figure 3' is a diagrammatic illustration of another iorm of the invention in which thyr'atrop orphotofiood lamp socket. This impedance serves to reduce the voltage across the lamp during the modeling or preparatory stage. lamp or bulb operates at below rated voltage.

When the photograph is about ,to be taken and the shutter is open, a supernormal voltage is then impressed upon the filament so as to produce a peak of supernormallum'inosity' Because of the high peak luminosity as compared with the modeling illumination obtained from the'lamp's', the shutter may be set for any desired time, such as a full se'cond,'if desired,'and afterthe shutter is opened, the closing of the operating swlit'oh'of thefsystem of the present invention will'produce the supernormal luminosityfor a very'sh'ort' time with the camera shutter open. Thereafterftlfe" shutter may be closed.' Thus, by'mea'iisol' the present invention anexposui'e of approximately- .Therefore, the

3 V25 of a second is obtained with the shutter open for a much longer period as desired.

The current flowing through the lamp is sufficiently great to melt the filament or heater element of the lamp if permitted to flow continuously. For a short period of time the surface of the filament is heated to such an extent that extremely high luminosity is obtained. This characteristic is aided when alternating current is used by the skin effect, that is, the current density at the surface of the filament or conductor is greater than the density in the center thereof. The thermal capacity of the filament is such that the filament is not heated throughout the thickness thereof sufiiciently to melt it within the short period of time used.

Considering the present invention. more particularly, it provides an impedance coil in series with the photofiood lamps which reduces the operation of the lamp or lamps to below the rated voltage during the modeling or preparatory stages and the same impedance coil is subsequently employed to have a supernorrnal voltage generated therein which is imposed upon the high amperage The present invention also providesclosed only for a time, permitting the filaments to reach the desired supernormal peak luminosity for'thedesired time. Thus, the present system may be designed to provide an exposure of about ,6 of a second or the like. 1

Referring more particularly to the drawings, the'wires H3 and I! may be connected to any suitable source of A. C. voltage, such as the customary household 110 volts. The bulbs or bulb sockets l2, two being shown in parallel, are connected on one side to line In through a manual switch 13 and a fuse I4, it being understood that any number of such bulbs can be employed. The winding 15 of the transformer is interposed in line; Thus the winding 15 serves as an impedance or choke coil to reduce the voltage across the bulbs or bulb sockets to below the rated voltage. The primary winding [6 of the transformer isconnected to the Wire 10 at the point I! and to the wire I I by means of the wire E8, the latter, I

however, having interposed a variable resistance 50- and a normally open switch comprising a fixed contact [9 and a movable contact 20.

Thus, when the switch [3 is closed, the fiood lights will operate below normal voltage and serve to provide the desired light for modeling. Whenswitch I9, 20 is closed, a high voltage will be. induced in winding l5 which is additive to theline voltage and the incandescent filaments will reach a high supernormal peak luminosity.

The variable resistance 58 controls and may.

be employed. to adjust the high voltage across the photofiood bulbs 12 to the desired value. The neon glow lamp 52 bridging part of the potentiometer resistor 5i serves to indicate when the voltage across the photofiood lamps I2 equals the desired predetermined value. The resistor 50 and glow lamp 52 provide a check and a means for maintaining the apparatus in good operating condition.

The present invention provides for an automatic control of the switch I9, 20 so as to maintain the same closed only for the desired time from one-tenth to one-hundredth of a second. For this purpose the movable contact 20 is carried by the armature 2| of the relay 22. One side of the relay winding 22 is connected to the line wire H3 through a resistance 23 and rectifier 24 and wire 25. The other side of the winding 22 is connected to the other line wire ll through the manual switch 26 and wire 21. A condenser 28 is connected as shown across the winding 22 and the switch 26.

In operation the line wires i 6 and H are plugged with the source of line voltage and the switch 13 is closed. The winding I5 of the transformer serves as an impedance and the bulbs l2 operate at below normal voltage. At this time the condenser 28 becomes charged to its maximum voltage by a charging circuit which includes wire 25, rectifier 24, resistance 23, condenser 28 and wire 27. When the exposure is made, the switch 26' is closed and the condenser 28 discharges through the switch 26 and relay 22. This I moves the armature 2| to close the switch I9,

28 thereby connecting the winding is across the mains. voltage induced therein, which is additive to the line voltage so as to produce a voltage of perhaps 175 volts or the like across the photofiood bulbs i2. When the condenser 28 has discharged or its voltage is reduced substantially by the discharge, the winding 22 is de-energized and the switch [5, 25 is opened. By means of this sys- A tern, therefore, the switch I9, 20 is automatically opened at a predetermined time, preferably ,5 of a second, after it is closed.

Because the filaments had been maintained hot and their circuit is not interrupted it can be brought to the supernormal peak luminosity within a time delay of less than 20 milliseconds after the high voltage is applied.

It will now be seen that thepresent system provides for the employment of a minimum of parts. One winding of the transformer is employed both to provide the high voltage and the impedance for the bulbs. The size of the transformer is considerably reduced by the present system because a large percentage of the supernormal voltage is obtained directly from the line. In the present apparatus the initial or preliminary voltage applied to the filaments during the modeling stage may be varied by varying the reluctance in the core of the transformer, as by changing or adjusting the air gap in the core or The time of energizain the core laminations. tion of the relay winding 22 can be controlled by varying its resistance, or by varying the size of the condenser, 'or by varying the voltage to which the condenser is charged.

When the relay 22 is energized and the cone tacts i9, 28 are closed, the reactance of coil l5 is reduced to a low value and the voltage induced therein is built up rapidly. This voltage adds to the line voltage across the bulbs and causes themto glow at an exceedingly high intensity for the.

duration of time the relay is closed. By limiting the duration of the high intensity illumination to the short period of time and partially as a result of the latent heat of fusion of the'filament, burn out is avoided. The present unit can be synchronized with any camera shutter which ;;has contacts that close when the shutter is The winding l5 has a relatively high T me e openedi Such shutter contacts could then be used as the: switch126, to thereby obtainautomatic synchronization of the flasher the: photofiood lamps.

Where the camera, shutter does not have. contacts; but instead: is operated by a solenoid, the optional wiring arrangementof the control circuiti shown in Figure 2 may be employed. In this figure the box corresponds to that part of the system shown in Figure l which is included withinthe dottedline box 30. The elementsof' the control shown in Figure l and which also appear inFigure 2 bear the same referencecharenters.-

the wiring diagram shownrin Figure 2 when theswitch 32, a. double pole single throw switch, is closed to? operate the shutter and to: create a; flash, thecondenser 28 is'discharged through the relay 22, throughiwire 33, switch 32 and Wire 34. The? closing of the switch 32 also energizes the shutter operatingsolenoid 35' through the circuit which includes wire 31, rectifier 24 solenoid 35 and voltage dropping resistor 36. The solenoid thus: acts essentially insynchronization with the relay 22. The. voltage. dropping, resistor 36 reduces the voltage across the solenoid coil to the-desiredvalue. The by-pass resistor 38 is desirablein the event that the solenoid coilisnot plugged in, in which case it. provides a current pathto charge the condenser. The resistance of 38-15 very'hlghcolnpared to the resistance; 0f.solenoidcoil 35.

Figure 3 shows. a system which is analogous to: the system. shown in Figure 1. except that i instead of. a relay 22" and contacts- IS, 20 operated thereby; one or two' thyratrons' 40' are employed, as shown. In this system the thyratrons arenor mally biased to out ch. When the switch 26 is closed, condenser'zll discharges throughthe primary' winding: 4| of the transformer which is provided with two secondaries 42 and 43, one of.

these two secondaries 42, 43, connected in the grid circuit of each thyratron- 40. The oscillationggeneratedin the circuit which includes the condenser 28- and the: primary winding-'14! are thereby transferred to the grids of the thyra.-- trons and cause the same to fire, thus effectuallyconnecting the windin [6 to the line; The thyratrons continue: firing. until the oscillations dampen out to below the firing potential of the thyratrons'; The: time of firing is controlled by the characteristics. of the transformer; 4 I 42, 43.

The use of a transformer for illuminating a flash bulb: is; not always essential.

or. a second, or thereabouts, when connected across the terminals of a normal line voltage; say 110 volts; could b'eus'ed, as clearly illustrated in- Figure 4; For example, two- 32 volt flash lamps H2 may be used to produce afiash when connected across 110 volt circuit. The voltage supplied to the'lamps H2 may be reducedfto' 20 volts or some other: subnormal l voltage by' means" For example, a. flash: bulb that would flash in a. period of /2 the electromagnetl 22, the switch l9 will again" be: opened, in that the current flowing. through the leakage circuitincluding the rectifier 24- and the. resistance 23 is insufficient to hold the elec tromagneti'lL Although the preferred embodiment'of the de: vice has beendescr-ibed, it will be: understood that within the purview of this invention various changes. may bemade inthe. form, details', proportionand arrangement of par-ts, the combina tion' thereof andmode of operation, which gen erally'statedconsistin a device'capableof carrying out the objects set forth, as disclosed anddefined in the appended claims.

Having' 'thus described our invention, we claim:

1. In. an illuminating apparatus for photo-- graphic purposes employing high luminosity incandescent filament lamps, the" combination-of a receptacle for said lamp, a-transformer having? two windings, one winding being connectedin series with said receptacle and serving to reduce the voltage impressed upon said receptacle to substantially below the rated voltage of the lamp, the second winding being normally open circuited, and electric control means operable response to the closing of its circuit to' close the circuit of the second winding" and to open thesame after the lapse of a predetermined srnalli fraction of a second.

2. Ihe apparatus set forth in claim 1 in which the lastnamed means comprise a condenser and circuit means receiving a discharge from said condenser, said circuit means'includinga sv'vitcli for opening and closing the second winding, the

' discharge serve to actuate said circuit to close and open the second winding circuit.

3; In an illuminating apparatus for photographic purposes employing a high luminosity incandescent filament lamp, the combination of an electrical receptacle for said lamp, a transformer having a primary winding connected in parallel with said receptacle and normally open circuite'd and a secondary winding connected in series with said receptacle and serving to reduce the voltage at the receptacle, and electric control means for closing and opening" said primary" winding.

4. The apparatus set forth in claim? in which incandescent filament lamp, the combination of" a receptacle for said lamp, a transformer having two windings, one winding connected in series; with the receptacle, means for connecting said receptacle and second winding to a voltage source, the second winding connected in parallel with the receptacle, the circuit of said second winding being normallyopen, and electric control meansfor closing the circuit of said second winding the'reby'generating in the one winding" a volta e in a manner to add the same to't he'" voltage of the source, so as to caus'e'the filament" lamps to flash momentarily then said electric control means opening the circuitthrough the second winding.

6. In an illuminating apparatus for photographic purposes employing high luminosity" incandescent filament lamps, the combination of a receptacle for said lamp, a transformer having two windings, one winding being connected in series with said receptacle and serving to reduce 7.1 the voltage impressed upon said receptacle tov substantially? below the rated voltage. of the lamp, thesecond winding being normally open circuited, and control means to close and open the circuit of the second winding, said control means closing the circuit of the second winding to cause the filament lampsto flash momentarily then open circuiting the second winding.

7 The method of illuminating objects for, photographic purposes by the employmentof an incandescent. filament lamp having a normal voltage substantially equal to normal line volt. age, the steps of impressing upon the lamp a voltage substantially below its rated voltage, charging a condenser, discharging the condenser through a relay, said relay altering the circuit through the lamp so as to impress upon the terminals or" the lamp a voltage sufficiently high to cause a current to flow through the filament of the lamp, generating sufficient heat to melt the filament if permitted to continue, the condenser upon being discharged permitting the relay to open the circuit through the lamp before sufficient heat has been generated in the filament to melt the same.

8. In an illuminating apparatus for photographic purposes employing a high luminosity incandescent filament lamp, the normal voltage of the filament lamp being substantially equal to the normal line voltage, the combination of a receptacle for said lamp, a transformer having a primary winding and a secondary winding, the primary winding being connected in series with said receptacle and serving to reduce the Voltage impressed upon said receptacle to a voltage substantially below the rated voltage of the lamp, the secondary winding being normally open circuited, and electric control means including a condenser and a rectifier connected in series across the terminals of the line and in parallel with the primary winding of the transformer and the filament of the lamp, a relay and a switch connected in series across the terminals of the condenser so that as the switch is closed the condenser discharges through the relay, said relay actuating a switch for connecting the secondary windings of the transformer across the terminals of a filament so as to increase the voltage impressed upon the terminals of the filament to cause a current of sumcient magnitude to melt the filament if permitted to continue to flow, the relay open circuiting the secondary winding upon the condenser being discharged so as to have a voltage across the terminals less than the voltage required to hold the relay switch closed.

9. In a photofiash illuminating apparatus employing an incandescent lamp or lamps, means for applying a subnormal voltage to said lamp or lamps, and means for applying a supernormal voltage for a predetermined interval of time to said lamp or lamps, said last mentioned means including a relay, a condenser, a switch for connecting the condenser across the terminals of the relay, and a leakage circuit for charging the condenser, the closing of the switch causing the condenser to energize the relay so as to supply a supernormal voltage to the lamp or lamps, the current through the leakage circuit being insufficient to hold the relay so that the relay interrupts the supernormal voltage upon the condenser being discharged.

10. In an illuminating apparatus employing an incandescent lamp or lamps, means for applying i a predetermined voltage to said lamp or lamps,

means for varying said voltage, and means for automatically limiting the time of application thereof to obtain a change in luminosity for said lamp or lamps for apredetermined interval of time, said last mentioned means including a relay for actuating a switch to vary the voltage, a condenser, a leakage circuit for charging the condenser, and a switch for connecting the condenser across the terminals of the relay, the current through the leakage circuit being insufiicient to actuate the relay, the charge on the condenser upon the last mentionedswitch being closed energizing the relay to vary the voltage supplied to the lamp or lamps until the condenser has been discharged at which time only the predetermined voltage is applied to the lamp or lamps.

11'. In a photofiash illuminating apparatus employing an incandescent lamp or lamps, means for applying a predetermined voltage to said lamp or lamps, and means for adding a supernormal voltage to said lamp or lamps to produce a flash, said last mentioned means automatically limiting the time of application thereof for apredetermined interval of time, said last mentioned means including a condenser, a leakage circuit for charging the condenser, a relay, and a switch for connecting the condenser across the terminals of the relay, the current required to hold the relay being greater than the current normally fiowing through the leakage circuit so that as the switch is closed causing the condenser to discharge through the relay the relay causes a supernormal voltage to be applied to the lamp or lamps only until the condenser has been discharged.

12. In a photofiash illuminating apparatus including an incandescent lamp or lamps, an electric circuit connected to the source of energy having a voltage input substantially higher than the voltage required to illuminate the lamp or lamps under normal operating conditions, said circuit including an impedance connected in series with the lamp or lamps was to reduce the voltage supplied to the lamp or lamps to a subnormal voltage, and circuit means for applying the line voltage directly to said lamp or lamps for a predetermined interval of time so as to cause a flash thereof, said last mentioned means including a relay, a condenser, a switch for connecting the condenser across the terminals of the relay, and a leakage circuit for charging the condenser, the leakage circuit including a rectifier and an impedance for reducing the current flow so that the current flowing through the leakage circuit is insufiicient to energize the relay but sufilcient to charge the condenser, the closing of the switch causing the condenser to energize the relay so as to apply the line voltage to the lamp or lamps until the condenser is substantially discharged through the relay at which time the relay interrupts the flow of line voltage to the lamp or lamps thereby interrupting the flash thereof.

- ROBERT A. STEIN.

LEE S. WASSERMAN.

No references cited.

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