US2395600A - Means to ignite photographic flash lamps - Google Patents

Description

Feb. 26, 1946. was 2,395,600

I MEANS TO IGNITE PHOTOGRAPHIC FLASH LAMPS Filed April 14, 1945 Fig:

Lou/s We/s glass INVENTOR.

BY WwM/W ATTORNEY Patented Feb. 26, 1946 UNITED STATES PATENT OFFICE MEANS TO IGNITE PHOTOGRAPHIC FLASH LAMPS 3 Claims.

This invention pertains to a novel means of igniting photographic flash lamps.

Photographic flash lamps consist of a glass vessel filled with oxygen and containing aluminum or magnesium in some suitable form (usua y thin wire or thin foil). A filament, usually coated with a combustible substance, is provided, and the combustion of the metal is initiated by electrically heating the filament. On portable photographic equipment, such as hand cameras, the current for this purpose is supplied by dry baty.

A certain time elapses between the instant when the operator closes the electric circuit and the time when the ignited aluminum or magnesium emits the peak of its light emission. This time lag is usually approximately twenty milliseconds and is longer than the time necessary to open an average photographic shutter which usually requires approximately seven milli-seconds. Therefore, mechanical devices called "synchronizers are used by means of which the electrical circuit is closed and the shutter opened with the proper time interval so that the lamp is approximately at the peak of its light emission for the duration of the shutter opening. The design of these synchronizers does not form part of this invention and a detailed description is therefore omitted.

Synchronizers very frequently do not function as consistently as desirable and the time which elapses between the closing of the circuit and the peak light emission varies so that very often the combustion of the aluminum or magnesium has already progressed too far or not far enough when the photographic shutter is actually wide open.

It has been found that this is almost entirely due to the fact that the internal resistance of a battery increases appreciably with age. A new battery has a very low internal resistance enabling it to supply a high current to the filament, thus starting the combustion within a very short time. The internal resistance of an older battery increases more or less slowly during its useful life and increases very rapidly thereafter so that the battery becomes useless, i. e. the internal resistance becomes eventually so high that the current passing the filament will not render it sufllciently hot to initiate the combustion at all.

The operator has no means of judging whether a given battery is still good enough to effect proper synchronization and even if a battery is lamp considerably slower than a substantially new battery.

The use of a dry battery has other disadvantages. Dry batteries suitable for this purpose are relatively heavy and bulky and this disadvantage becomes worse when it is desired to ignite several flash bulbs simultaneously. In certain regions it may also be difllcult to obtain dry batteries for replacement and other disadvantages inherent to the use of dry batteries can be readily visualized.

For that reason it has occasionally been suggested to use small generators which are actuated either by a hand crank or the like or which are driven by a spring motor and which are supposed to deliver sufllcient electric energy to initiate the combustion of the photographic flash bulb as described above. These attempts have not been successful heretofore chiefly due to the fact that the generator would have to be fairly large and that also provisions have to be made to rotate it with a constant speed since otherwise its voltage would not be constant and consequently the combustion would not be initiated with a constant time lag.

This generator must, of course, be rotated during the actual exposure and it will be clear that a rotating generator mounted on a hand camera is quite undesirable since even a very small well balanced generator is apt to introduce vibrations.

It is the purpose of this invention to overcome these difliculties by providing a system which can be operated either by a battery, but which in this case can be very much smaller and which will function independently of its condition or age, or which can be operated by a generator but without the disadvantages outlined in the preceding paragraphs.

I accomplish this by energizing the filament by means of which the combustion is initiated not directly from either a battery or a generator but from a suitable condenser (or capacitor) which in turn is charged prior to the exposure either from a battery or a generator.

The invention is illustrated by means of the accompanying drawing in which preferred embodiments are disclosed diagrammatically and in which Fig. l is a circuit diagram embodying the igniting means, with a dry battery as a current generator;

Fig. 2 is a modifled circuit diagram in which a hand operated current generator is used;

still "good enough" it still may ignite a flash as Fig. 3 is a schematic cross section through the generator along the plane of line 3-4 in Fig. 2; and

Fig. 4 is a schematic cross section through a commutator of the generator along the plane of line H in Fig. 2.

Like characters of reference denote similar parts throughout the several views and the following specification.

The general scheme of a battery operated capacitator for this purpose is shown in Fig. 1. II is a small dry battery. I2 is a condenser of suitable electrical dimensions. I3 is a single pole switch connecting the battery to the condenser. 14 is another single pole switch which is normally open and which preferably is actuated by a pusn button. I5 is a flash bulb. I la is a small resistor which limits the current flowing from the battery to the lamp when push button switch I! is closed.

I have found that with a battery of 2.6 volts, a capacitator of 2000 microfarad will safely and reliably ignite flash bulbs of standard type such as commercially available.

The method of operation is quite simple. Whenever the camera is to be used, switch I3 will be closed by the operator. This connects the battery to the condenser which will be charged up to the battery voltage. The time necessary for this charge is usually less than a second, but even a fraction of a second is an extremely long time as compared to the discharge time which is ordi narily of the order of approximately two milliseconds. Consequently the current which the battery is called upon to deliver is less that 1% of the current which it would have to deliver to the flash lamp filament directly if used in the ordinary manner. This tends to prolong the life of the battery and makes it possible to use a much smaller battery.

The battery may be left connected to the condenser for prolonged periods of time such as seve eral hours since the leakage current of commercially available condensers, once they are charged, is quite small so that the drain on the battery is negligible. Whenever the camera is stored away, of course, it is advisable to disconnect the battery from the condenser.

It will be clear that once the condenser is charged, it is merely necessary to depress push button H in order to ignite the flash bulb. Push button I, of course, can be mechanically connected to a synchronizer in the usual manner but since the synchronizer proper does not form part of this invention, this connection is not shown in the diagram.

It will be found that the function of this system is for all practical purposes entirely independent of the age or of the internal resistance of the battery. An old battery will merely take a longer time to charge the condenser.

This can be easily demonstrated by connecting a resistor in series with the battery, thus artificially increasing the resistance of the condenser charging circuit, and I have actually added as much as 1000 ohms without in any way Jeopardizing the charging of the condenser and the subsequent ignition of the flash lamp.

If the condenser has the proper electrical dimensions, the stored energy is so large and the internal resistance of the condenser discharge circuit is so extremely low that it will ignite the filament within one or two milli-seconds. This has two advantages: First, it reduces the time lag from the time of closing the circuit to the peak emission of the lamp from the customary twenty milli-seconds to approximately 12 which faciliassaooo tates the design of a proper synchronizer, and second, it makes for practically 100% consistent results, since it will be obvious that if the time to ignite the filament amounts to only two milliseconds, any possible fluctuation of this small time will be negligible as compared to the total time lag of approximately twelve milli-seconds. In other words, the time lag may vary approxi mately between eleven and twelve milli-seconds which is not nearly enough to throw the system out of proper synchronization, whereas with the old method of using the battery directly I have found the time may vary between fifteen and thirty milli-seconds which obviously very often completely destroys the synchronization.

Fig. 2 shows the condenser as energized by a generator. A hand crank ll drives a large gear I! which in turn drives a small gear II. The small gear is held between two thrust bearings so that it cannot shift axially and a rather steep thread is cut into its center hole. This thread engages the generator shaft which is equipped with a corresponding male thread and which has sufllcient axial play to permit a shift of approximately Va. The generator rotor is is otherwise quite conventional and consists of a suitably shaped piece of soft iron surrounded by a coil of copper wire. The two ends of the coil are connected to a commutator 20 which again is quite conventional except that its segments are rather short. An auxiliary contact 2| is provided which is normally open and which will be closed as soon as the generator shaft moves in the direction of the arrow which it will do as soon as crank It is rotated. 22 is a condenser. 23 is a flash bulb and 24 is a normally open contact. The generator rotor is surrounded by a permanent magnet of conventional design which is not shown in this diagram.

The operation of this device is as follows:

Prior to exposure, the operator turns hand crank it several times. This causes gears l1 and I8 to rotate which forces the rotor first to shift axially to close contact 2|, and then to rotate. This generates an electrical current charging capacitator 22. After the operator ceases to rotate hand crank it, the rotor will return to its original position since it is biased by a spring provided for this purpose which however is not shown in the drawing. The opening of switch 2! prevents the condenser from discharging -again through the rotor windings themselves. For the same reason the commutator segments have been made quite short so that the condenser during the charging period is connected to the rotor coils only during the peak of the generated sine waves.

After the condenser is charged, it will keep its charge for a fairly long period of time, usually several minutes, and the operator merely has to push switch 24 in order to ignite the flash bulb.

I have found that the best conditions for a generator operated system can be obtained with a generator voltage of approximately 70 volts and a condenser capacity of approximately 20 microfarads.

It will be clear that a. generator energized system of this type avoids all the disadvantages outlined before, and that vibrations are no longer a problem since the generator is merely rotated prior to the exposure and is standing still during the exposure itself.

As long as the speed of the generator is above a certain speed, it will charge the condenser to a certain minimum voltage which, of course, must be chosen so high that it will ignite the filament with certainty. The minimum speed can easily be assured by providing a suitable gear transmission so that the operator simply cannot fail to provide at least this minimum speed and usually a great deal more. One then has the same conditions as above, 1. e. the time necessary to ignite the filament may vary from one to two milliseconds which again is negligible compared to the total time of twelve milli-seconds and which in no way will jeopardize the proper synchronization.

It will be understood that the generator circuit as shown is merely an example which can be modified in many ways which will be obvious to one skilled in the art. For example, instead making the small gear ll act as a nut and the generator shaft as a screw, gear ll can be fastened directly to the shaft it gears l1 and I8 are helical gears which when rotated also exert a thrust in the direction of the arrow so that switch ll becomes closed during the rotation of the generator. It is also possible to close switch 2| by a centrifugal governor so that the generator is again automatically disconnected from the condenser as soon as the generator ceases to rotate. Switch 2| may also be replaced by a suitable rectifier, preferably, 01' the copper oxide or selenium type. Modifications of this nature should be considered to fall within the scope oi this invention.

Various other changes in details and disposition of parts may obviously be resorted to without departing from the principles or sacrificing any of the advantages oi! the invention as defined in the appended claims. a

What I claim as new, is:

1. In combination with a photographic flash Patent No. 2,395,600.

, I Itiis hereby certified that the inventor, said We' lass,

Summon, Jaelcson enfite'lnterest therein, as shown by th said Letters Patent should and sealed this 7th day LOUIS WEISGLASS the above numbered patent was erroneously issuedto whereas said patent should have been issued 'to" ezghis, New York, as assignee by meme assignments lamp consisting of a light transmitting vessel containing a filament and a plurality of components adapted to combine chemically upon heating of said filament, a low voltage dry battery of small size and weight 0! the type which deteriorates with age to generate electric energy, a condenser for storing said energy, and means to discharge said stored energy into said vessel to heat said filament to initiate chemical combination of said components.

2. In combination with a photographic flash lamp consisting 01' a light transmitting vessel containing a filament and a plurality of components adapted to combine chemically upon heating of said filament, an electric circuit having a low voltage dry battery of small size and weight of the type which deteriorates with age to generate electric energy, a condenser for storing said energy, and means to discharge said energy from said condenser into said vessel, including a switch interposed between said condenser and vessel, to heat said filament to initiate chemical combination of said components.

3. In combination with a photographic fiash lamp consisting of a light transmitting vessel containing a filament and a plurality of components adapted to combine chemically upon heating of said filament, a low voltage dry battery of small size and weight of the type which deteriorates with age generating electric energy, a condenser adapted to be charged with electric energy from said battery, and means to discharge electric energy from said condenser to heat said filament to initiate chemical combination of said components.

LOUIS WEISGLASS.

Certificate oi Correction February 26, 1946.

qfthe a record of assignments in this oifice; and that the be read with this correction form to the record of the case in the Patent Oflice.

of May, A. D. 1946.

therein that the same may con- LESLIE FRAZER,

First Assistant Commissioner of PM,

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