JP2003315879A - Camera with built-in stroboscope - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a reduction in cost of a product. <P>SOLUTION: A xenon discharge tube 31 whose outside diameter (d) is 2.5 mm is used and also an IGBT 53 is provided as a means for stopping discharge to the tube 31 in a light control circuit 44. A choke coil 45 where impedance is set so that a maximum current flowing in a stroboscopic circuit 41 may be equal to or under the allowable current of the IGBT 53 is positioned. When the charge voltage of an integration capacitor 55 attains a specified level, the IGBT 53 is turned off and the discharge to the tube 31 is stopped. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a xenon discharge tube for emitting strobe light, and a dimming circuit for stopping discharge to the xenon discharge tube when the integrated amount of reflected light from a subject reaches a predetermined level. The present invention relates to a camera having a built-in strobe device.

[0002]

2. Description of the Related Art Inexpensive and easy-to-use simple cameras such as compact cameras, instant cameras, digital still cameras, and film units with lenses have become popular.
Most of such simplified cameras have a built-in strobe device to enable shooting at night or indoors. This strobe device discharges the electric charge charged in the main capacitor in the xenon discharge tube in conjunction with the shutter operation,
By irradiating the subject with the strobe light generated at this time, the brightness of the subject is increased and the exposure amount is increased.

Some strobe devices as described above are provided with an automatic light control function called a so-called auto strobe. In this auto strobe device, the xenon discharge tube is made to emit light, and at the same time, the amount of light reflected from the subject is received by a light receiving element such as a phototransistor, the photoelectric current generated by this is integrated, and this integrated amount is set to a predetermined level A light control circuit that stops the discharge to the xenon discharge tube at the time of reaching is reached, so that the amount of strobe light is appropriately adjusted according to the distance to the subject.

Conventionally, a contactless switch such as a thyristor has been used as a means for stopping the discharge to the xenon discharge tube. However, in order to operate this thyristor normally, in addition to the gate voltage, there is a temperature dependence. It was necessary to configure a complicated analog circuit for making the gate current and the holding current of large values appropriate. For this reason, recently, F
An IGBT (Insulated Gate), which is a switching element capable of controlling a large current at high speed, having both the small power control characteristic of ET and the current characteristic of a transistor.
Bipolar Mode Transistor, insulated gate bipolar transistor).

When the IGBT is used as a means for stopping the discharge to the xenon discharge tube, there is an advantage that the structure of the analog circuit is simpler than that of the thyristor. However, the allowable current of the IGBT is about 150 A, which is smaller than that of the thyristor. Therefore, when using the IGBT, use it together with a xenon discharge tube with an outer diameter of 2.5 mm or less and a high internal impedance to create a closed loop of the strobe circuit. The impedance is increased and the current in the circuit is suppressed below the allowable current of the IGBT.

[0006]

The xenon discharge tube having an outer diameter of 2.5 mm or less has advantages such as a reduced size of the strobe device and good light emission efficiency, but strict accuracy is required for vertical alignment of electrodes. Product yield is poor, such as
It has the disadvantage of high product cost. Therefore, when using a xenon discharge tube as described above in a simple camera, especially a film unit with a lens whose low price is for sale,
The cost will increase.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a camera with a built-in strobe capable of realizing cost reduction of a product.

[0008]

In order to solve the above-mentioned problems, the present invention detects a xenon discharge tube that emits strobe light toward a subject and the amount of reflected light from the subject, and the integrated amount thereof is set to a predetermined value. In a camera having a built-in strobe device including a dimming circuit for stopping discharge to the xenon discharge tube when the level is reached, the xenon discharge having a tube outer diameter of 2.5 mm or more. A tube is used, and the dimming circuit is provided with an IGBT as a means for stopping discharge to the xenon discharge tube.

The sensitivity of the photographic film used is I
SO1600 or more is preferable. It is preferable that a choke coil or a resistor is provided in the strobe circuit, and the impedance of the choke coil or the resistor is set so that the maximum current flowing in the strobe circuit is equal to or less than the allowable current of the IGBT.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an overview of a lens-fitted film unit embodying the present invention. Inside the unit main body 3 of the lens-fitted film unit 2, various photographing mechanisms such as a shutter mechanism and a film feeding mechanism, a strobe device 21 (see FIG. 2) and the like are incorporated, and an unexposed photo film and a photographed film are taken. A film cartridge including a cartridge for storing a photographic film is loaded at the time of manufacture. In this film unit with lens 2, IS
A high-sensitivity film of O1600 or more is loaded.

On the front surface of the unit body 3, there are provided a taking lens 4, a viewfinder objective window 5, a protector 6, a strobe operation knob 7, and a light receiving window 8 for automatic light control. Further, a release button 9, a counter window 10 for displaying the number of remaining photographable frames, and a charge display window 11 for displaying the completion of charging are provided on the upper surface of the unit body 3. Further, a winding knob 12 that is rotated for each frame is exposed on the back surface, and a viewfinder eyepiece window (not shown) is provided at a position facing the viewfinder objective window 5. An opening for exposing the taking lens 4, the viewfinder objective window 5, the protector 6 and the like to the outside is provided on the front surface of the unit body 3.

The strobe operation knob 7 is used for the strobe device 2.
The charging switch 26 (see FIG. 2) of No. 1 is interlocked with the charging switch 26. After the completion of charging, when the release button 9 is pressed with the strobe operation knob 7 in the on position to perform photographing, the protector 6 emits strobe light toward the subject in synchronization with this operation. When the strobe operation knob 7 is slid downward from the ON position and set to the OFF position shown in the drawing, the strobe does not emit light and normal photographing is performed. Although the presence / absence of strobe light emission is selected by slidingly moving the strobe operation knob 7, for example, a button type operation member may be provided and pressed.

FIG. 2 shows an exploded perspective view of the strobe device. The strobe device 21 includes a strobe light emitting section 22, a substrate 23 on which various components constituting the strobe circuit 41 (see FIG. 3) are mounted, a main capacitor 24, a synchro switch 25, a charging switch 26, a battery contact 27, and a light emitting diode 28. Etc.

The stroboscopic light emitting section 22 has a substantially box-shaped reflector case 29, a reflector 30 housed inside the reflector case 29, a xenon discharge tube 31, and the reflector case 2.
It is composed of a protector 6 attached to the front surface of 9. The xenon discharge tube 31 includes a glass tube 31a in which xenon gas is sealed, and electrodes 3 provided on both sides.
It is composed of 1b and 31c, and its outer diameter d is 2.5mm.
Is. The xenon discharge tube 31 is connected to a trigger electrode 48 (see FIG. 3) provided on the back surface of the reflector 30. A trigger voltage is applied to the inside of the xenon discharge tube 31 via the trigger electrode 48.

The substrate 23 comprises a main substrate 23a and a sub-substrate 23b fixed so as to be substantially perpendicular to the main substrate 23a. A phototransistor 32 is mounted on the sub-board 23b as a light receiving element for receiving the reflected strobe light. This phototransistor 32 has a light receiving window 8
It is arranged behind the camera and receives the reflected light from the subject and generates a photoelectric current according to the received light intensity. The main capacitor 24 stores the accumulated charge in the xenon discharge tube 31.
It is used to discharge flash light. The main capacitor 24 is set to have a smaller capacity than that normally used and has a large internal resistance.

The synchro switch 25 is composed of a pair of metal contact pieces 25a and 25b, and horizontally protrudes from the main board 23a. The synchro switch 25 is used as a switch for strobe light emission, and is turned on when a shutter mechanism (not shown) is activated. The charging switch 26 includes a movable piece 26a and a fixed piece 26b, and is attached to a position corresponding to the strobe operation knob 7. The movable piece 26a is operated by operating the strobe operation knob 7.
Comes into contact with the fixed piece 26b, and strobe charging is started.
The battery contact piece 27 is composed of a pair of metal contact pieces 27a and 27b. The metal contact pieces 27a and 27b contact the both electrodes of the AA dry battery 29 having an electromotive force of 1.5 V, for example, and supply electric power to the strobe circuit 41.

The light emitting diode 28 lights up when the main capacitor 24 is charged to a specified charging voltage. The light emitted from the light emitting diode 28 is guided to the charging display window 11 through a light guide (not shown). The photographer can know the completion of charging by turning on the light emitting diode 28 observed through the charging display window 11.

FIG. 3 shows a circuit configuration of the strobe device 21. The strobe circuit 41 is the main capacitor 2 described above.
In addition to the battery 4, the battery 29, and the flash discharge tube 31, the oscillation booster circuit 42, the trigger circuit 43, the dimming circuit 44, and the choke coil 45 are included. The oscillation booster circuit 42 constitutes a known blocking oscillation circuit. This blocking oscillator circuit operates when the charging switch 26 is turned on, and the high voltage generated during this operation charges the main capacitor 24.

The trigger circuit 43 includes a trigger capacitor 4
6, a trigger coil 47, and a trigger electrode 48. The trigger capacitor 46 is charged by the output current from the oscillation booster circuit 42. When the IGBT 53 is turned on, the electric charge accumulated in the trigger capacitor 46 flows to the primary side of the trigger coil 47, and a trigger voltage of, for example, about 4 kV is generated on the secondary side of the trigger coil 47, and this trigger voltage causes the trigger electrode 48 to flow. Through xenon discharge tube 31
Applied to. As a result, dielectric breakdown occurs between the electrodes of the xenon discharge tube 31, the charge of the main capacitor 24 is discharged in the xenon discharge tube 31, and strobe light is generated.
The protector 6 irradiates the subject.

The dimming circuit 44 comprises a light receiving circuit 51, a timer circuit 52, an IGBT 53, a comparator 54 and the like. The light receiving circuit 51 includes a phototransistor 32, an integrating capacitor 55, and the like. The phototransistor 32 receives the strobe light reflected from the subject and generates a photoelectric current according to the received light intensity.

The timer circuit 52 is provided for a period of time from when the charging switch 26 is turned on to when the phototransistor 32 stabilizes, and in order to prevent the phototransistor 32 from malfunctioning due to the influence of noise when the trigger voltage is generated. There is. After the elapse of a predetermined time by the timer circuit 52, the integrating capacitor 55 is charged by the photoelectric current generated in the phototransistor 32, and the integrating capacitor 55 is charged.
A charging voltage corresponding to the amount of received light is generated at.

The IGBT 53 has a collector terminal connected to the xenon discharge tube 31 and a base terminal connected to the output terminal of the comparator 54. The comparator 54 starts its operation when the synchro switch 25 is turned on, and the IGBT 53
Turn on. As a result, strobe emission by the xenon discharge tube 31 is started. Then, the integration capacitor 55
When the charging voltage of the IGBT reaches a predetermined level, the IGBT53
Is turned off to stop the discharge to the xenon discharge tube 31. In this way, the stored charge of the main capacitor 24 is used in a required amount, and when the next charge is performed, the main capacitor 24 has a residual charge, so that the battery 29 can be prevented from being consumed. In addition, stable flash photography can be performed with a simpler circuit configuration than when a contactless switch such as a thyristor is used.

The impedance of the choke coil 45 is
The maximum current flowing through the flash circuit 41 is set to be equal to or less than the allowable current of the IGBT 53. Further, as described above, the internal resistance of the main capacitor 24 is also larger than usual for the same purpose as the choke coil 45. The capacitor 56 is for supplying power to the comparator 54.

Next, the operation of the above configuration will be described. When performing nighttime photography or indoor photography, the photographer slides the strobe operation switch 7 to the on position. As a result, the charging switch 26 is turned on and the oscillation booster circuit 42 is turned on.
Starts to operate, and the secondary side output charges the main capacitor 24 and the trigger capacitor 46, respectively.
When the main capacitor 24 reaches the specified charging voltage, the light emitting diode 28 lights up. The photographer confirms the lighting of the light emitting diode 28 through the charging display window 11, determines the photographing range through the viewfinder, and then presses the release button 9 to perform photographing.

When the release button 9 is pressed, the shutter mechanism operates and the synchro switch 25 is turned on. At the same time, the comparator 54 starts to operate and the IGBT 5
Turn on 3. Then, the trigger voltage generated in the trigger coil 47 is applied to the xenon discharge tube 31 via the trigger electrode 48, and the electric charge accumulated in the main capacitor 24 is discharged through the xenon discharge tube 31. Xenon discharge tube 3
The strobe light generated in 1 is emitted from the protector 6 toward the subject.

When strobe light is applied to a subject, a part of the reflected light passes through the light receiving window 8 and the phototransistor 3
Incident on 2. In the phototransistor 32, a photoelectric current having a magnitude corresponding to the intensity of reflected light from the subject flows, and the photoelectric capacitor charges the integration capacitor 55. Then, when the charging voltage of the integrating capacitor 55 reaches a predetermined level, the IGBT 53 is turned off, and the xenon discharge tube 3
The discharge to 1 is stopped. Therefore, even if the distance to the subject is short or the reflectance of the subject is high, the strobe is prevented from fully emitting, and the subject illuminated by the strobe light or the room light is not used as the light source without the lighting effect of the strobe light. Even with such a background, it is possible to reproduce an appropriate density on the photograph. Of course, even when the distance to the subject is long, an appropriate amount of strobe light can be emitted.

When the main capacitor 24 having a smaller capacity than usual is used as in the above embodiment, there is a concern that the amount of strobe light will be insufficient.
Since the high-sensitivity film of 0 or more is used, there is no fear that the amount of strobe light will be insufficient.

The oscillation booster circuit 42 and the trigger circuit 43 of the strobe circuit 41 may have any structure as long as the charge of the main capacitor 24 flows into the xenon discharge tube 31 by the application of the trigger voltage. A resistor may be used instead of the choke coil 45. Further, in the above embodiment, the lens-fitted film unit has been described as an example, but the present invention is not limited to this, and the present invention is also applied to a simplified camera such as a compact camera, an instant camera, or a digital still camera. be able to.

[0029]

As described above, according to the camera with a built-in strobe of the present invention, a xenon discharge tube having an outer diameter of 2.5 mm or more is used, and the dimming circuit stops the discharge to the xenon discharge tube. An IGBT is provided as a means, and a choke coil or a resistor whose impedance is set so that the maximum current flowing in the strobe circuit is less than the allowable current of the IGBT is provided, so stable stroboscopic photography can be performed with a simple circuit configuration. Is. Therefore, the cost of the product can be reduced, which may contribute to the miniaturization of the product. Further, since the sensitivity of the photographic film used is ISO 1600 or higher, there is no fear that the amount of strobe light will be insufficient.

[Brief description of drawings]

FIG. 1 is a schematic view of a lens-fitted film unit embodying the present invention.

FIG. 2 is an exploded perspective view of a strobe device.

FIG. 3 is a diagram showing a configuration of a strobe circuit.

[Explanation of symbols]

2 Film unit with lens 9 Release button 21 Strobe device 24 Main capacitor 25 Sync switch 26 Charge switch 31 xenon discharge tube 41 Strobe circuit 42 Oscillation booster circuit 43 Trigger circuit 44 dimming circuit 45 choke coil 51 Light receiving circuit 53 IGBT 54 comparator

Claims (3)

[Claims] 1. A xenon discharge tube that emits strobe light toward a subject, and a quantity of reflected light from the subject is detected, and when the integrated amount reaches a predetermined level, the discharge to the xenon discharge tube is stopped. In a camera having a built-in strobe device having a strobe circuit with a dimming circuit incorporated therein, the xenon discharge tube having an outer diameter of 2.5 mm or more is used, and the dimming circuit is connected to the xenon discharge tube. A camera with a built-in flash, which is provided with an IGBT as a means for stopping the discharge of the flash. 2. The sensitivity of the photographic film used is ISO
The camera with a built-in strobe according to claim 1, characterized in that the number is 1600 or more. 3. The choke coil or resistor is provided in the strobe circuit, and the impedance of the choke coil or resistor is set so that the maximum current flowing in the strobe circuit is equal to or less than the allowable current of the IGBT. Item 1. The camera with a built-in flash according to Item 1 or 2.