GB2121973A - Electronic flash device - Google Patents

Abstract

An electronic flash device employs a flash discharge tube X powered directly from a flat multicelled battery E. An automatic illumination control circuit 3 effects photoelectric conversion and integration of the light reflected from a pictorial object. When the integral reaches a predetermined value the control circuit 3 provides an illumination stop signal to terminate the illumination. A timer circuit 4 also provides an illumination stop signal after the expiration of a given time. The illumination from the flash discharge tube X is thence terminated in response to a stop signal from either the automatic illumination control circuit 3 or from the timer circuit 4, whichever occurs first. <IMAGE>

Description

SPECIFICATION Electronic flash device The present invention relates to an electronic flash device for photography, and more particularly, to an electronic flash device having automatic illumination control facilities.

In the accompanying drawings: Figure 1 is a graph depicting the characteristics of a conventional electronic flash device having automatic illumination control; and Figure 2 is a graph depicting the characteristics of a conventional electronic flash device of the direct type without such control.

A conventional electronic flash device having automatic illumination control capabilities uses an ordinary dry cell as a power source, together with a booster circuit such as a DC-DC converter for charging a primary storage capacitor to a high voltage suitable for discharging electrical energy through a flash tube. The flash provides illumination which is continued until the integral of the light reflected from the pictorial object and subjected to photoelectric conversion reaches a predetermined value. In this type of electronic flash device, the electrical energy stored in the primary capacitor is momentarily discharged, so that illumination characteristics of the device are such that the duration of illumination (t) is short and the luminance (V) is increased suddenly and decreased rapidly as shown in Figure 1.If the pictorial object is close to the camera, it often happens that the flash illumination, which should end at the point of time A in Figure 1, continues up to point B, thus causing an overexposure. As a further disadvantage, the primary storage capacitor takes several to ten-odd seconds to become fully charged, so multiple flashes cannot be provided to effect high-speed motor drive photography. Furthermore, the booster circuit, the primary storage capacitor and other associated circuits add to the size and weight of the overall flash device.

Japanese Patent Publication No. 10533/66 describes an electronic flash device of the direct illumination type which does not include a primary storage capacitor, and which instead powers a flash discharge tube to provide illumination directly using a nickel-cadmium cell or a lowimpedance power source. This flash device has the illumination characteristics shown in Fig. 2, and unlike the above described first type of electronic flash device, this device provides continuous illumination of a low but constant luminance, the amount of which can be controlled very easily and precisely. As a further advantage, the absence of the time necessary to fully charge a primary capacitor enables multiple flashes, and the omission of associated circuits such as the booster and primary capacitor helps reduce the size and weight of the flash device.

This type of electronic flash device may have a built-in automatic light control mechanism as disclosed in U.S. Patent No. 4 184 756, corresponding to Japanese Patent Application (OPI) No. 62700/80 (the symbol OPI as used herein indicates an unexamined published Japanese patent application); the device includes a gate connected in series with a flash discharge tube and further connected to a gate control circuit that integrates the light reflected from the pictorial object, and, when the integral reaches a predetermined value, closes the gate to stop the illumination from the flash discharge tube. When the pictorial object is far from the camera, the light reflected from the object is so weak that the device continues to provide illumination for a very long time until the reflected light reaches the predetermined value.Under such conditions, the desired effect of stroboscopic photography is not achieved and the power source of the electronic flash device is simply wasted.

A general object of the present invention is to provide an improved electronic flash device.

According to the invention there is provided an electronic flash device, comprising means powered directly from a multi-celled battery to provide illumination, automatic illumination control means for effecting photoelectric conversion and integration of light reflected from a pictorial object to provide a first signal for terminating illumination and timer means for providing a second signal for terminating illumination whereby illumination is terminated in response to the first-occurring first or second signal.

In a preferred form the invention provides an electronic flash device, comprising a flash discharge tube for providing illumination, said discharge tube being powered directly from a multicelled battery, an automatic illumination control circuit for effecting photoelectric conversion and integration of light reflected from a pictorial object and which, when said integration reaches a predetermined value, issues an illumination stop signal, and a timer circuit for issuing an illumination stop signal after the expiration of a given time, the flash discharge tube illumination being terminated responsive to said illumination stop signal from either the automatic illumination control circuit or said timer circuit, whichever issues that signal first.The flash discharge tube provides automatically controlled illumination, if necessary with multiple flashes, when powered directly from a flat multicell battery and makes most effective use of the energy available.

In a practical construction the device is embodied as a compact lightweight unit primarily since a bulky heavy primary storage capacitor is unnecessary.

The invention may be understood more readily, and various other features of the invention may become apparent from consideration of the following description.

An embodiment of the invention will now be described with reference to Figures 3 and 4 of the accompanying drawings, wherein: Figure 3 is a schematic circuit block diagram showing an electronic flash device made in accordance with the present invention; and Figure 4 is a cross section of a small flat multicelled battery suitable for use in the electronic flash device of the present invention.

As shown in Figure 3 the device has a flash discharge tube X, a discharge trigger means circuit 1 , a discharge switching means circuit 2, an automatic illumination control means circuit 3, a timer means circuit 4 and a discharge stopping means circuit 5. A high-voltage, small, flat multicelled battery E powers the device. The battery E may have the same layer arrangement as a commercial product sold under the tradename "POLAPULSE". As illustrated in Figure 4, the battery E is preferably made up of 150 to 200 manganese cells each consisting of a zinc layer 50, a manganese oxide layer 52 and an interposed electrolyte-filled nonwoven fabric sheet 51.

Adjacent celis of the battery are electrically connected to each other by means of an intercellular conductive film 53. With this arrangement, the multicell flat battery E provides a voltage of about 250 volts with a very small internal resistance, so a large current can be drawn therefrom. The discharge trigger means circuit 1 comprises a trigger capacitor TC, a trigger coil TL and a trigger thyristor SCR,. When the thyristor SCR, is turned on, a trigger pulse is applied to the trigger electrode of the flash discharge tube X to enable the latter. The discharge switching means circuit 2 includes a transistor Q" and thyristors SCR2 and SCR3. The thyristor SCR2 is connected in series with the tube X and both thyristors SCR, and SCR2 need gate inputs to cause the tube X to strike an arc.

When a conventional X-contact signal from the associated camera is provided to terminal m, the transistor 0,, is turned on to provide a trigger pulse for the gates of both thyristors SCR, and SCR2 therebyto initiate illumination from flash discharge tube X. Conversely a stop signal from the discharge stopping means circuit 5 turns on the illumination-stopping thyristor SCR3 which discharges the stored energy of capacitors C3 and C4 to reverse-bias the thyristor SCR2, which is then turned off to stop the illumination from flash discharge tube X. At the same time, the thyristor SCR3 discharges the stored energy of capacitors C6 and C6 and reverse-biases the thyristor SCR, to disable the trigger electrode.The circuit 2 also includes a resistor R and a capacitor C7 for turning the thyristor SCR3 back off after a predetermined time interval. The resistance of R is set at a value that permits a current flow of not more than the retention current of thyristor SCR3 when the capacitor C7 is discharged.

The automatic light control means circuit 3 provides a first signal i.e. a first illumination stop signal with a timing proport'anal to the intensity of the light reflected from the pictorial object. The circuit 3 comprises a sensitometric photo-detector SPD for detecting the light reflected from the pictorial object, an operational amplifier OP for amplifying the light current generated in the SDP, an integrating capacitor C1, a switch in the form of a transistor Q2 for initiating the charging of the capacitor C1, and a comparator Com 1 having a non-inverting input terminal P connected to the integrating capacitor C1, and an inverting input terminal 0 which is effectively furnished with photographic information from the camera such as the film speed or aperture, through the input terminal n.

The timer means circuit 4 provides a second signal i.e. a second illumination stop signal after the expiration of a predetermined time period. The circuit 4 comrpises a flip-flop FF, an integrating capacitor C2 and a comparator Com 2. The output of terminal a of the flip-flop FF is normally off and that of terminal b is normally on. When a set terminal S receives the X-contact signal from the terminal m the outputs of the output terminals a, b are inverted, and upon receiving a reset signal at reset terminal R, the inverted outputs return to the original state. The non-inverting input terminal P' of the comparator Com 2 is connected to the integrating capacitor C2, and the interting input terminal Q' is again furnished with photographic information from the camera via the input terminal n.

The discharge stopping driver circuit 5 includes transistors Q3 and Q4 connected to the gate of the illumination-stopping thyristor SCR3 through an OR gate in the form of a pair of diodes D, and D2.

The transistor Q3 is turned on in response to the output from illumination control circuit 3 to provide a trigger signal applied to the gate of the thyristor SCR3, and the transistor Q4 is turned on in response to the output from timer circuit 4 to provide a trigger signal applied to the gate of thyristor SCAR3.

The operation of the electronic flash device of Figure 3 is as follows: If a main switch MS is closed, the whole device is enabled for operation, but the light control circuit 3, the timer circuit 4, the discharge stopping driver circuit 5, the discharge triggering circuit 1 and the discharge switching circuit 2 are at rest. When the shutter button on the camera is depressed, the shutter opens and an X-contact signal is fed to terminal m. Transistor Q is turned on and a trigger voltage is applied to the gates of thyristors SCR, and SCR2 to turn them on and activate the tube X. An arc current then flows through flash discharge tube X to provide illumination. At the same time, the X contact signal is fed to the set terminal S of flip flop FF, whereupon the outputs at terminals a and b of F are inverted to turn transistor Q2 off. This permits the charging of integrating capacitors C, with a current proportional to the intensity of the light reflected from the pictorial object. The integrating capacitor C2 of the timing circuit 4 is also charged with a constant current. When the voltage across the capacitor C, at the non inverting input terminal P of the comparator Com 1 exceeds the voltage at the inverting input terminal 0, the output from the comparator Com 1 is inverted to generate an illumination stop signal that momentarily turns on the transistor Q3. As a result, a trigger pulse is provided to the gate of the comparing a resultant integration value with a camera output setting value to initiate the first signal.

4. A device as claimed in any one of claims 1 to 3, wherein the means providing illumination is a flash discharge tube and there is further provided means for triggering said discharge tube, said triggering means including a trigger capacitor and a triggering thyristor activated in response to a camera generated X-contact signal.

5. A device as claimed in claim 4 and further comprising discharge switching means for deactivating the discharge tube and discharge stopping means for providing said first and second signals or responsive thereto to control said switching means.

6. A device as claimed in claim 5, said discharge switching means comprises of a thyristor for stopping said illumination in response to either of said first and second signals.

7. A device according to claim 4, wherein a further thyristor is connected in series with said tube and is triggered in response to said cameragenerated X-contact signal.

8. A device according to claim 7, wherein there is provided discharge switching means with an illumination stopping thyristor with a gate electrode connected via an OR-gate to receive the first and second signals and capacitors which serve to switch off the triggering and further thyristors when the illumination stopping thyristor is rendered conductive.

9. A device according to claim 8 and further comprising means for automatically re-setting the illumination-stopping thyristor to a nonconductive state after a pre-determined time from its activation in response to the first or second signal.

10. A device as claimed in any one of claims 1 to 9, wherein said timer means comprises flip-fiop means, integrating means and comparator means for comparing a resultant integration value with a camera output setting value to initiate the second signal.

11. A device as claimed in claim 3, wherein the automatic illumination control means also has switch means for enabling the integrating means and said timer means comprise flip-flop means, integrating means and comparator means for comparing a resultant integration value with a camera output setting value to initiate the second signal, said flip-flop means controlling said switch means of the illumination control means 12.

12. An electronic flash device, comprising a flash discharge tube for providing illumination, said discharge tube being powered directly from a multicelled battery, an automatic illumination control circuit for effecting photoelectric conversion and integration of light reflected from a pictorial object and which, when said integration reaches a predetermined value, issues an illumination stop signal, and a timer circuit for issuing an illumination stop signal after the expiration of a given time, the flash discharge tube illumination being terminated responsive to said thyristor SCR3 to turn the thyristor SCR3 on. The capacitors C3 and C4 are then discharged to reverse-bias the thyristor SCR2 whereupon the arc current through flash discharge tube X is cut off to terminate the illumination.The thyristor SCR, is turned off by the discharge through the capacitors C6 and C6. The thyristor SCR3 is turned off again when the discharge through capacitor C7 is completed.

When the voltage across the integrating capacitor C2 at the non-inverting input terminal P' of the comparator Com 2 exceeds that at the inverting input terminal Q', the transistor Q4 is turned on in response to the resulting stop signal and a trigger pulse is provided to the gate of the thyristor SCR3. The illumination from the flash discharge tube X is then terminated in the manner described above. Since the outputs of the transistors 03 and Q4 are fed to the gate of the thyristor SCR3 through the OR gate D1 and D2, the illumination from the flash discharge tube X is terminated in response to a stop signal from the automatic light control circuit 3 or from the timer circuit 4, whichever occurs first.The discharge stop signal from the comparator Com 2 is fed back to the reset terminal R of the flip-flop FF so the outputs thereof revert to the initial state, the transistor Q2 is turned on and the entire flash device is ready for operation.

When the pictorial object is close to the camera, the illumination is controlled by the automatic light control circuit 3, while for a more distant object, the timer circuit 4 will terminate the illumination after a predetermined time elapses.

The device has the following advantages: 1) very accurate control over the illumination is possible; 2) if the pictorial object is far from the camera, the device terminates illumination after the lapse of a given time without wasting battery energy; 3) the device does not require a bulky and heavy primary storage capacitor; so, 4) the device can be embodied as a compact, lightweight automatic strobe capable of providing multiple flashes.

Claims (1)

1. An electronic flash device, comprising means powered directly from a multi-celled battery to provide illumination, automatic illumination control means for effecting photoelectric conversion and integration of light reflected from a pictorial object to provide a first signal for terminating illumination and timer means for providing a second signal for terminating illumination whereby illumination is terminated in response to the first-occurring first or second signal.

2. A device as claimed in claim 1, wherein said multicelled battery is a flat-type battery providing a substantially constant luminance-time characteristic.

3. A device as claimed in claim 1 or 2, wherein said automatic illumination control means comprises reflected-light sensing means feeding integrating means, and comparator means for illumination stop signal from either the automatic illumination control circuit or said timer circuit, whichever issues that signal first.

13. An electronic flash device substantially as described with reference to, and as illustrated in Figure 3 of the accompanying drawings or Figures 3 and 4 of the accompanying drawings.