JPH0122716B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatically controlled electronic flash device that stops flashing from a flash tube in response to a control signal from a photometric integration circuit including a photosensitive element.

In a general auto strobe, which is a so-called auto strobe that has an automatic light control function, the amount of exposure at a short distance is greater than the amount of exposure at a far distance. That is, there is a tendency for overexposure to occur when the light emission guide number (a value that practically indicates the amount of light from a photographic flash light source) is low, and various methods have been proposed to prevent this.

One method is to suppress exposure on the short distance side by outputting a light emission control signal before the film reaches proper exposure. However, this method has the disadvantage that the farther the distance, the less exposure there is.

In view of the above points, the present invention was made to eliminate such drawbacks, and its purpose is to compensate for the lack of exposure on the long distance side, and furthermore, to ensure proper exposure over the entire range from short distances to long distances. An object of the present invention is to provide an electronic flash device that can be obtained.

In order to achieve such an objective, the present invention
A delay circuit is provided that has a delay time corresponding to the time from flash occurrence to the generation of the control signal from the photometric integration circuit, and the flash tube is activated after the delay time of the delay circuit after receiving the control signal. Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a circuit diagram showing an embodiment of an electronic flash device according to the present invention. The high voltage generating section, main capacitor, light emission starting section, etc. are the same as those of a conventional auto strobe, so they are omitted, and only the parts necessary for explanation are omitted. shows.

In the figure, X _e is a flash tube, T _h1 is a thyristor forming the first switching element, T _h2 is a thyristor forming the second switching element for stopping light emission, and R ₁ to R ₁₀ are resistors. The internal resistance R ₂ is a small resistance for generating the power supply V ₂ for the light emission stop circuit, and its resistance value is set to about 30 mΩ. P _d is a photodetector (photosensitive element), C ₁ to _{C 7} are capacitors, and capacitor C ₅ is an integration capacitor that integrates _the photocurrent;
constitutes a photometric integration circuit together with the light receiving element _Pd . Further, a time constant circuit is configured by capacitor C ₆ and resistor R ₈ and capacitor C ₇ and resistor R ₁₀ . COMP is a comparator, Q ₁ is a transistor, Q ₂ is a field effect transistor (FET), and Q ₃ is a transistor.

and TC is a trigger capacitor connected in series with the primary side of the trigger coil TCL; S is a switch for causing the flash tube X _e to generate a flash (hereinafter referred to as light emission); R ₁ and C ₁ are a resistor and a capacitor connected in series, and this series circuit of resistor R ₁ and capacitor C ₁ is connected in parallel to the flash tube X _e .

Thyristor T _h1 , which is the first switching element
The anode side of the flash tube X _e and trigger coil TCL
and the connection point of capacitor C ₁ , the cathode side is grounded via resistor R ₂ , and connected via diode D to a constant voltage circuit consisting of a Zener diode ZD and capacitor C ₃ connected in parallel, and the gate The electrode is grounded via a resistor R ₃ and connected to the connection point between the resistor R ₁ and the capacitor C ₁ via a capacitor C ₂ and a resistor R ₄ in series. In addition, the anode side of the thyristor T _h2 , which is the second switching element for stopping light emission, is connected to the connection point of the resistor R ₁ and the capacitor C ₁ , the cathode side is grounded, and the gate electrode is connected to the connection point between the resistor R 1 and the capacitor C 1.
It is grounded through _C4 and resistor _R5 in parallel.

Non-inverting input terminal of comparator COMP (positive potential input terminal)
(+) is connected to the connection point of the photodetector P _d and the integrating capacitor C ₅ , which are connected in series between the power supply V ₁ and the ground.
The inverting input terminal (negative potential input terminal) (-) is connected to the slider of a variable resistor VR which is connected between the power supply _V1 and the ground and generates a reference voltage (comparison voltage) _Vth .
A switch SW for preventing malfunction is connected in parallel to the integrating capacitor _C5 , which is turned off at the same time as the flash tube _Xe emits light. Here, this switch SW is constituted by a mechanical or electronic switch.

Transistor Q ₁ is connected to the drain of FET Q ₂ , its emitter is grounded, and its base is connected to the output of the comparator COMP through resistor R ₆ , and
Grounded through resistor _R7 . Also, FETQ ₂
The source of is connected to the base of transistor Q ₃ ,
The gate is connected to the above Zener diode through a time constant circuit consisting of a capacitor _C6 and a resistor _R8 connected in parallel.
It is connected to a constant voltage circuit consisting of ZD and capacitor _C3 , and is also grounded via resistor _R9 .
The emitter of the transistor Q ₃ is connected to the constant voltage circuit, the collector is connected to the gate electrode of the thyristor T _h2 , which is the second switching element, and the base is made up of a capacitor C ₇ and a resistor R ₁₀ connected in parallel. It is connected to the constant voltage circuit via a time constant circuit. Then, by using FETQ ₂ that changes the turn-on time and a time-setting circuit consisting of capacitor C ₆ and resistor R ₈ and capacitor C ₇ and resistor R ₁₀ , the control signal from the photometric integration circuit is transmitted from the light emission of flash tube X _e . A delay circuit is configured that has a delay time corresponding to the time until the occurrence of .

Next, the operation of the embodiment shown in FIG. 1 will be explained with reference to FIGS. 2 to 6. First, when the switch S is closed, the charge in the trigger capacitor TC is rapidly discharged through the primary side of the trigger coil TCL.
A high pressure of KV is generated, which partially ionizes the gas inside the flash tube X _e and lowers the internal resistance, inducing a main discharge and causing the flash tube X _e to emit light. At the same time, switch SW
is turned off, the light receiving element _Pd receives the light reflected from the subject, and the photocurrent is integrated by the capacitor _C5 . When the terminal voltage of the capacitor _C5 reaches the reference voltage (constant value) _Vth set by the variable resistor VR, a high level "H" control signal is sent from the comparator COMP, and the transistor _Q1 transition to the on state.

In this way, in the present invention, the light receiving element P _d
photocurrent or the corresponding current in the capacitor
It has a comparator COMP that integrates by C ₅ and issues a control signal when the voltage reaches a constant value V _th , but this control signal is generated before the exposure of the film surface reaches the appropriate value. is configured to be This method uses an integrating capacitor C ₅
Either make the capacitance smaller or use a reference voltage (comparison voltage).
This is achieved by lowering V _th .

On the other hand, at the same time as the flash tube X _e emits light, the capacitor
Due to the discharge of _C1 , the thyristor _Th1 shifts to the on state, and the voltage generated across the resistor _R2 is applied via the diode D to the constant voltage circuit consisting of the Zener diode ZD and the capacitor _C3 . The output voltage of the constant voltage circuit becomes the power supply V ₂ , and this power supply
Start charging capacitor C ₆ by V ₂ . Here, the potential V _G at the intersection of this capacitor C ₆ and resistor R ₈
is applied to the gate of FETQ ₂ . and,
As shown in FIG. 2, which is an operation explanatory diagram in which time t is plotted on the horizontal axis and potential V _G is plotted on the vertical axis, _the potential V G decreases with the passage of time.

When a high level “H” control signal is generated from the comparator COMP and transistor _Q1 is turned on,
The source-drain resistance R _SD of FETQ ₂ depends on the current potential V _G and increases with time as shown in FIG. 3. In this way, transistor Q ₁ is turned on, and capacitor C ₇ is charged through the source-drain resistance R _SD of FET Q ₂ . This charging current is determined by the source-drain resistance R _SD of FETQ ₂ .
Therefore, the time during which the transistor _Q3 is turned on, that is, the delay time T from when the control signal is input from the comparator COMP until the transistor _Q3 is turned on, changes in accordance with the time from light emission.

Then, when the transistor _Q3 is turned on, the power supply _V2 is applied to the gate electrode of the thyristor _Th2 , so the thyristor _Th2 is turned on, and accordingly, the thyristor _Th1 is turned off, and the flash tube X _e goes out.

Figure 4 shows the relationship between the time _t from the time the flash tube X _e emits light until the control signal is input, and the delay time T from the time the light emits light until the transistor Q ₃ turns on. In the waveforms, a', b', and c' indicate the manner in which the light emission stops when the control signal is input at times t ₁ , t ₂ , and t ₃ shown in FIG. 5B, respectively. In addition, T ₁ , T ₂ ,
T ₃ indicates the time from when the control signal is input until the light emission stops, time T ₁ indicates the delay time when it is bright, that is, when the distance is short, and time T ₂
indicates the delay time in the case of medium distance, and time _T3 indicates the delay time in the case of long distance.

As is clear from Fig. 5, the delay time T ₃ from the input of the control signal until the light emission stops is longer on the far side or on the side with a larger light emitting guide number, which reduces the underexposure on the far side. can do.

FIG. 6 shows this aspect. In the figure, the dotted line a indicates the case where no correction is made, that is, the control signal is issued to stop the light emission of the flash tube _Xe when the film surface reaches the proper exposure, and the dashed line c
shows the case in which a control signal is issued to stop the flash tube _Xe from emitting light before the exposure of the film surface becomes appropriate in order to prevent too much overexposure on the far side, and the solid line b shows the case according to the present invention. This shows the case where a control signal is issued before the film surface is properly exposed, and as the distance increases, the delay time is increased to stop the flash tube X _e from emitting light. It is. In the figure, E _V indicates the exposure amount on the film surface, O indicates the appropriate level, and DIS indicates the distance.

As is clear from Fig. 6, the flash is generated by the control signal obtained by reducing the capacitance of the photocurrent integration capacitor _C5 or by lowering the reference voltage (comparison voltage) _Vth . When the light emission of the _tube .
However, over medium to long distance ranges, the increased light intensity is reduced by the photocurrent integration capacitor _C5 .
This is smaller than the reduction in light amount due to the smaller capacity, resulting in underexposure. In order to compensate for this lack of exposure, as you move from medium to long distances, it is necessary to not stop the light emission immediately even when a control signal is received.
The flash tube X _e is configured to stop emitting light after a predetermined delay time by a delay circuit consisting of a FET Q ₂ which works together with a time setting circuit to change the time during which the transistor Q ₃ is turned on. In other words, the delay time is increased as the distance increases or as the time until the control signal arrives increases. The characteristics of the electronic flash device of the present invention constructed in this way are shown by the solid line b in FIG.

As is clear from the above description, according to the present invention, the photocurrent of the light receiving element or the current corresponding to it is integrated into the capacitor without using complicated means, and the voltage generated when the voltage reaches a constant value is generated. This system uses a control signal to control a transistor that changes its turn-on time, and stops the flash tube's light emission after a predetermined delay time. Since appropriate exposure can be obtained over a wide range over a long distance, the practical effect is extremely large.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of an electronic flash device according to the present invention, and FIGS. 2 to 6 are explanatory diagrams for explaining the operation of FIG. 1. X _e ...flash tube, P _d ...light receiving element, COMP...comparator,
Q ₁ ...transistor, Q ₂ ...field effect transistor,
_Q3 ...transistor, _C5 to _C7 ...capacitor, _R8 ,
R ₁₀ ...Resistance.

Claims (1)

[Scope of Claims] 1. In an automatically controlled electronic flash device that stops the flash of a flash tube in response to a control signal, a delay having a delay time corresponding to the time from generation of the flash of the flash tube to generation of the control signal. 1. An electronic flash device, further comprising a circuit that causes the flash tube to stop flashing after the delay time after receiving the control signal. 2. A delay circuit having a delay time corresponding to the time from generation of flash light of a flash tube to generation of a control signal, comprising a field effect transistor and a capacitor connected to the field effect transistor, and comprising a field effect transistor and a capacitor connected to the gate and source of the field effect transistor. The control signal is controlled such that the voltage between the flash tubes changes with time from the flash occurrence, and based on this, the source-drain resistance of the field effect transistor changes with time from the flash occurrence. The electronic device according to claim 1, wherein the capacitor is charged through the source-drain resistance of the field effect transistor, and the flashing is stopped when the accumulated charge reaches a constant voltage. Flash device.