JPH06222429A - Stroboscope with automatic dimmer - Google Patents

Abstract

PURPOSE:To provide a stroboscope with an automatic dimmer having a wide adjustable range of emitted light quantity from a flashing discharge tube and capable of finely adjusting the emitted light quantity. CONSTITUTION:In the stroboscope with the automatic dimmer which stops light emission from the flashing discharge tube by outputting a light emission stop signal in the case of detecting that appropriate exposure is attained according to light from an object, reference voltage Vref being any one of plural reference voltages is outputted to a comparator COMP by 1st and 2nd voltage switching parts 22 and 26. Meanwhile, the terminal voltage of an integrating capacitor integrating a current corresponding to the light from the object and capable of selecting capacity is outputted from an emitted light quantity detection part 28 to the other input of the comparator COMP. When a voltage signal from the detection part 28 attains the reference voltage Vref, the comparator COMP outputs the light emission stop signal. Namely, the switching of the reference voltage Vref and the switching of the capacity of the integrating capacitor are simultaneously performed, so that the range where the emitted light quantity from the flashing discharge tube can be adjusted, is widened and the emitted light quantity is finely adjusted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic light control strobe, and more particularly to an automatic light control strobe suitable for a wide aperture range of a camera.

[0002]

2. Description of the Related Art Generally, this type of automatic light control strobe is
Flash light is emitted from the flash discharge tube, light reflected from the subject is photoelectrically converted by the light receiving element, and the photocurrent is integrated by the integrating capacitor. When the voltage proportional to the amount of electricity (the amount of received light) integrated by the integrating capacitor reaches the reference voltage set corresponding to the current subject brightness, film sensitivity, etc., a light emission stop signal is output and the flash discharge tube is output. The light emission from is stopped.

By the way, as a method of adjusting the amount of light emitted from the flash discharge tube, there is a method of adjusting the reference voltage (Japanese Patent Laid-Open No. 59-7934). The device disclosed in Japanese Patent Laid-Open No. 59-7934 is designed so that an appropriate reference voltage is generated by an analog circuit according to the brightness of the subject.
Another method for adjusting the amount of light emitted from the flash discharge tube is to switch the capacitance of the integrating capacitor. For example, aperture value (F2.8, F4, F5.6, F
8) Integrating capacitors having different capacities are provided corresponding to 8), and any one integrating capacitor is selected by switch switching according to the current aperture value.

[0004]

However, in the case of adjusting the light emission amount from the flash discharge tube by adjusting the former reference voltage, for example, in the case of adjusting over a wide range of 8 steps from 2 to 10AV. , And the reference voltage at 2AV is V ₀ , the reference voltage at 10AV is 2
^It must be ⁸ × V ₀ . That is, if the reference voltage V ₀ at 2AV is 0.5 V, the reference voltage at 10AV is 1
It becomes 28V, and a battery-driven camera cannot cover the above voltage range. Therefore,
There is a problem that a wide step range cannot be adjusted by adjusting the reference voltage.

On the other hand, when the amount of light emitted from the flash discharge tube is adjusted by switching the integrating capacitors, a very large number of integrating capacitors are required if the step range is wide and finely adjusted. Since the integrating capacitor has product variations, the amount of light emitted from the flash discharge tube cannot be accurately adjusted only by the integrating capacitor, and a separate adjusting means is required.

The present invention has been made in view of the above circumstances, and an object thereof is to provide an automatic light control strobe in which the amount of light emitted from a flash discharge tube can be adjusted in a wide range and can be finely adjusted. To do. Another object of the present invention is to provide an automatic light control strobe capable of adjusting a desired light emission amount by a selection operation based on a plurality of bits of strobe light amount setting data.

Still another object of the present invention is to provide an automatic dimming strobe capable of easily adjusting the error in capacitance of a plurality of integrating capacitors.

[0008]

In order to achieve the above object, the present invention outputs a light emission stop signal and outputs a flash light discharge when it is detected that an appropriate amount of exposure has been reached based on incident light from a subject. In an automatic light control strobe for stopping light emission from a tube, reference voltage setting means for setting a plurality of reference voltages, photoelectric conversion means for outputting a current corresponding to incident light from a subject, and the photoelectric conversion means A plurality of integrating capacitors having different capacities for integrating the currents, and selecting one of the plurality of reference voltages based on the subject brightness, and selecting one of the plurality of integrating capacitors. And a means for selecting only one or a plurality of the integrating capacitors to integrate only the selected integrating capacitors, and detecting by integrating with the selected reference voltage and the selected integrating capacitors. Compares the detected voltage, it is characterized by comprising a comparison means for outputting the light emission stop signal and the detection voltage reaches the reference voltage.

Further, the selecting means includes means for generating strobe light amount setting data, which is composed of a first group bit and a second group bit and indicates an appropriate exposure amount, on the basis of subject brightness.
Select any one of the plurality of reference voltages based on the first group bit and select any one or more of the plurality of integration capacitors based on the second group bit. The feature is that only the selected integration capacitor is operable.

Further, the plurality of variable resistors respectively connected in series to the reference voltage setting means and one or a plurality of integrating capacitors selected by the second selecting means are used for the plurality of variable resistors. Means for selecting any one of the variable resistors and applying a voltage to the reference voltage setting means via the selected variable resistor.

[0011]

According to the present invention, the range in which the amount of light emitted from the flash discharge tube can be adjusted is wide by combining the selective switching of the reference voltage and the selective switching of the capacitance of the integrating capacitor.
And it is possible to make fine adjustments. That is, a plurality of reference voltage setting means for setting a plurality of reference voltages and a plurality of integration capacitors having different capacities for integrating a photocurrent indicating light from a subject are provided, and the plurality of reference voltages are set based on the subject brightness. One of the plurality of integration capacitors is selected, and at least one of the plurality of integration capacitors is selected to enable only the selected integration capacitor. Thereby, for example, the reference voltage for dividing the range of 1 or 2 steps can be set finely, and the range of 1 or 2 steps can be expanded by selecting the integrating capacitor.

According to another aspect of the present invention, the selecting means selects one of the plurality of reference voltages based on the first group bit of the strobe light amount setting data indicating the proper exposure amount. Since one or more of the plurality of integration capacitors are selected based on the second group bit and only the selected integration capacitor is operable, the strobe light amount setting data of a plurality of bits is selected. A desired amount of light emission can be adjusted by a selection operation (switching operation) based on.

According to still another aspect of the present invention, a plurality of variable resistors, each of which is connected in series to the reference voltage setting means, are provided, and any one of them selected by the second selecting means or Since the voltage is applied to the reference voltage setting means via the variable resistors corresponding to the plurality of integrating capacitors, the resistance value of the variable resistors can be substantially adjusted by adjusting the resistance value of the integrating resistors even if there is an error in the capacitance of the integrating capacitors. Capacitance error can be adjusted.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of an automatic light control strobe according to the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 is a block diagram of essential parts showing an embodiment of an automatic light control strobe according to the present invention. This automatic light control strobe adjusts the light emission amount from the flash discharge tube Xe according to the strobe light amount setting data applied from the camera side through the input terminal 10.
The light emission stop control unit 20 and the light emitting unit 30 are provided. still,
Since a charging unit for charging the main capacitor Cm of the light emitting unit 30, a light emission trigger unit for starting the discharge of the flash discharge tube Xe of the light emitting unit 30, and the like are well known, detailed description thereof will be omitted here.

When the high voltage is applied to the grid of the flash discharge tube Xe from the light emission trigger section after the main capacitor Cm has been charged, the light emitting section 30 starts the discharge in the flash discharge tube Xe to emit the flash light. Occur. At this time, the transistor Q ₆ and the transistor Q ₇ are turned off, and the transistor Q ₈ is turned on. Then, the light emission stop signal (“0”) is output from the comparator COMP of the light emission stop control unit 20.
(Level signal) is applied to the transistor Q ₆ of the light emitting section 30, the transistor Q ₆ is turned on and the transistor Q ₇ is turned on. When the transistor Q ₇ is turned on, the electric charge of the capacitor C is forcibly discharged, the transistor Q ₈ is turned off, the discharge in the flash discharge tube Xe is stopped, and the light emission is stopped.

Next, the strobe light amount setting data will be described. This strobe light amount setting data is a 3-bit (S _1, S _2, S ₃ ) digital signal indicating EV data,
Table 1 shows an example of the relationship between the aperture value (AV value) at the time of flash emission and the flash light amount setting data. As shown in the table, the adjustable range of the light emission amount is 2 to 5.
There are 3.5 steps up to 5 AV, and this range is set in 0.5 step increments.

Now, referring to FIG. 1, the light emission stop control unit 20.
Is a comparator COMP and a first voltage switching unit 22 for generating a reference voltage Vref applied to the positive input of the comparator COMP.
It comprises an adjusting unit 24 and a second voltage switching unit 26, and a light emission amount detection unit 28 which outputs a voltage signal corresponding to the flash light emission amount to the negative input of the comparator COMP. The first voltage switching unit 22 includes a second voltage switching unit 26 via the adjusting unit 24.
To set the applied voltage to the regulator 22
It is composed of A, resistors R ₁₀ and R ₁₁ , a transistor Q ₁ , a voltage follower 22B, and an inverter I ₁ , and the data of bit S ₂ of the strobe light amount setting data is added from the input terminal 10.

The regulator 22A receives power from a battery and outputs a predetermined constant voltage. In this circuit example, since a 6V battery is assumed, the regulator 22A uses a voltage 3 which is safe against fluctuations in the power supply voltage.
It is configured to output V. Resistance R ₁₀ and resistance R
₁₁ is the same resistance value, transistor Q ₁ is ON
Then, the voltage at the connection point A between the resistor R ₁₀ and the resistor R ₁₁ becomes 2
It is divided to 1 / 1.5 (1.5 V).

Therefore, the bit of the strobe light amount setting data
S₂Is "1", the inverter I₁Through
"0" is transistor Q₁Tran to join the base of
Dista Q ₁Is turned off, which causes the regulator 22
Voltage follower 22B with voltage 3V from A as it is
Is output via. On the other hand, the flash intensity setting data
Bit S₂Is "0", the inverter I₁Through
"1" is transistor Q ₁Tiger to join the base of
Register Q₁Is turned on, which causes the regulator 22
The voltage of 3 V from A is divided by half (1.5 V) and
It is output via the ltage follower 22B.

The adjusting unit 24 is a photo of the light emission amount detecting unit 28.
Transistor PT sensitivity and integration capacitor C_T1,C_T2
Of the transistor Q_2,Q₃,
Variable resistance VR_1,VR₂, And inverter I₂Composed of
Of the strobe light intensity setting data from the input terminal 10.
My bit S₁Data has been added. And
Bit S of strobe light intensity setting data₁When is “0”
"0" is the transistor Q₂To join the base of
Langista Q₂Is turned on, which causes the first voltage switching
The applied voltage from the part 22 is the transistor Q₂And variable resistance
Anti-VR ₁Is added to the second voltage switching unit 26 via.
On the other hand, bit S of strobe light intensity setting data₁Is “1”
In the case of inverter I₂“0” is a Transis via
Q₃Transistor Q to join the base of₃Is ON
As a result, the applied voltage from the first voltage switching unit 22
But transistor Q₃And variable resistor VR₂Second through
Of the voltage switching unit 26. In addition, with this adjustment unit 24
Details of the adjusting operation of will be described later.

The second voltage switching section 26 includes resistors R _0, R ₁ ,
It is composed of switches SW _{1 and} SW ₂ , and an inverter I ₃ , and the data of bit S ₃ of the strobe light amount setting data is added from the input terminal 10. The voltage applied through the adjusting unit 24 is the resistance R
It is divided by ₀ and the resistance R ₁ . Therefore, when the bit S ₃ of the strobe light intensity setting data is “0”,
Through an inverter I ₃ "1" is applied to the switch SW _1, the switch SW ₁ is ON, the voltage V ₀ which connection point C of the resistor R ₀ and the resistor R ₁ is output as the reference voltage Vref, On the other hand, the bit S ₃ of the strobe light intensity setting data
In the case of but "1", "1" is applied to the switch SW _1, the switch SW ₁ is turned ON, voltages V ₁ at point B is output as the reference voltage Vref.

By the way, the relationship between the resistance values of the resistors R ₀ and R ₁ is expressed by the following equation: 2 ^EV == (R ₀ + R ₁ ) / R ₀ ∴R ₁ = R ₀ (2 ^EV −1) ... (1) must be satisfied. Here, when the minimum bit S ₃ of the strobe light amount setting data changes from “0” to “1”, the set strobe light amount change amount (ΔEV) is set to ½ as shown in Table 1, The resistors R ₀ and R ₁
The relationship between and is determined by the following formula: R ₁ = R ₀ (2 ^1/2 −1) ≈0.414R ₀ (2)

Since 2 ^EV = (R ₀ + R ₁ ) / R ₀ = V ₁ / V ₀ (3), ΔEV (= 1/2) is determined by the voltage ratio. This voltage ratio does not change even if the voltage (V ₁ ) at the point B changes, because the resistors R _{0 and} R ₁ are fixed.
Now, the voltage V ₀ (reference voltage Vref) when the bits S _{2 and} S ₃ of the strobe light intensity setting data are both “0” is, for example,
In the case of 0.5V is between each bit S _2, S _3, the relationship between the reference voltage Vref output from the second voltage switching section 26 is as shown in the following table. When the bit S ₂ changes from “0” to “1”, the voltage set by the first voltage switching unit 22 is switched from 1.5 V to 3 V as described above. The voltage Vref is also doubled. That is, when the bit S ₂ is changed from “0” to “1”, the reference voltage Vref corresponding to the difference of 1 EV with respect to the reference voltage Vref before the change can be set.

The light emission amount detecting section 28 is mainly used for the phototraffic.
Transistor PT, integrating capacitor C having different capacitance
_T1, C_T2, Transistor Q_Four, Q_Five, And inverter I_Four
And the strobe light intensity setting from the input terminal 10.
Bit S of constant data₁Data has been added
It The phototransistor PT is the light from the subject (see above).
Reflected light from the subject and outside light),
A current proportional to the intensity of the received light is passed, and this current
Is the integration capacitor C_T1Or C_T2Is integrated by.

That is, the bit S of the strobe light amount setting data
₁Is "0", the inverter I_FourThrough “1”
Is transistor Q_FourTransis to join the base of
Q _FourIs turned on. As a result, the integration capacitor C_T1
Becomes operable and the phototransistor PT
Current is integrating capacitor C_T1Integrated by only. one
One, bit S of strobe light intensity setting data₁Is "1"
In case of “1”, the transistor Q_FiveJoin the base of
Therefore, transistor Q_FiveIs turned on. This gives the integral
Indexer C_T2Is enabled and the phototransistor
The current from the PT is the integrating capacitor C_T2Fucked by only
Be divided.

Here, the voltage at the point D is proportional to the integrated electric quantity Q (amount of received light) and inversely proportional to the capacity C of the integrating capacitor, as shown by V = Q / C. Therefore, the amount of received light can be set by switching the capacitances (C _T1 and C _T2 ) of the integrating capacitor. By the way, when the maximum bit S ₁ of the strobe light amount setting data changes from “0” to “1” (that is, when the integrating capacitor C _T1 is switched to the integrating capacitor C _T2 ), the step difference as shown in Table 1 is generated. Since the capacitance is increased by two steps, the capacitance relationship between the integrating capacitor C _T1 and the integrating capacitor C _T2 is given by the following equation: C _T2 = 2 ² × C _T1 = 4C _T1 (3) That is, the integration capacitor C _T2 may be selected to have four times the capacitance of the integration capacitor C _T1 .

The accumulated charges in the integrating capacitors C _T1 and C _T2 are discharged by a short circuit (not shown) before strobe light emission. The voltage at the point D of the light emission amount detector 28 is applied to the negative input of the comparator COMP. As described above, the reference voltage Vref is applied to the positive input of the comparator COMP from the second voltage switching unit 26. The comparator COMP compares these inputs and the voltage of the negative input reaches the reference voltage Vref. Then, the light emission stop signal “0” is output to the light emitting unit 30 to stop the light emission.

Next, the adjusting operation in the adjusting section 24 will be described. Variable resistance VR ₁ or V of the adjusting unit 24
By adjusting the resistance value of R ₂ , the reference voltage Vref output from the second voltage switching unit 26 can be adjusted. Now, when the bit S ₁ of the strobe light amount setting data is “0”, the integration capacitor C _T1 becomes operable in the light emission amount detecting unit 28, and the adjusting unit 24 applies the voltage from the first voltage switching unit 22. The voltage is applied to the second voltage switching unit 26 via the transistor Q ₂ and the variable resistor VR ₁ .

Therefore, the sensitivity of the phototransistor PT and the variation of the integration capacitor C _T1 can be compensated by adjusting the reference voltage Vref by the variable resistor VR ₁ . For example, when each bit (S ₁ , S ₂ , S ₃ ) of the strobe light intensity setting data is (0, 0, 0), the strobe light intensity at that time is 2A as shown in Table 1.
The resistance value of the variable resistor VR ₁ may be adjusted so as to correspond to V.

Similarly, when the bit S ₁ of the strobe light amount setting data is “1”, the light emitting amount detecting section 28 enables the integrating capacitor C _T2 and the adjusting section 24 has the first voltage switching section. voltage applied from the 22, the second voltage through the transistor Q ₃ and the variable resistor VR ₂ switching section 2
6 will be added. Therefore, this variable resistor VR
By adjusting the reference voltage Vref with ₂ , the sensitivity of the phototransistor PT and the variation of the integration capacitor C _T2 can be compensated.

For example, when each bit (S ₁ , S ₂ , S ₃ ) of the strobe light amount setting data is ( ₁ , 0, 0),
As shown in Table 1, the resistance value of the variable resistor VR ₂ may be adjusted so that the amount of strobe light at that time corresponds to 4AV. As described above, according to this embodiment, the light emission amount for 3.5 steps is set to 0.5 E according to the strobe light amount setting data.
It can be set in steps of V steps.

In this embodiment, the integration capacitor C _T1 and the integration capacitor C _T2 are switched, but the invention is not limited to this. The integration capacitor C _T1 is always allowed to integrate and the integration capacitor C _T2 is operated. It may be switched to enable or disable. However, in this case, it is necessary to select the capacitance of the integration capacitor C _T2 so that the total capacitance of the integration capacitor C _T1 and the integration capacitor C _T2 is four times the capacitance of the integration capacitor C _T1 .

In this embodiment, the first voltage switching unit 22 and the second voltage switching unit 26 are used to set the reference voltage Vref, but the present invention is not limited to this.
Only the second voltage switching unit may be used. Further, the step width (ΔEV) corresponding to the minimum bit and the step range in which the light amount can be set may be various combinations, and are not limited to the present embodiment.

FIG. 2 is a block diagram showing another embodiment of the second voltage switching unit 26 of FIG. 1, in which ΔEV is (1/8) E.
This is shown for the case of V. The second voltage switching unit 40 is composed of resistors R _{0 to} R ₇ and a switch circuit 42. The switch circuit 42 includes resistors R _{0 to} R ₇
8 voltages V _{0 to} V ₇ divided by 3 and 3 bits S _31, S ₃₂ , S instead of the above-mentioned minimum bit S _3.
33 data is added, and the switch circuit 42 outputs the voltage V _0- based on the data of each bit S _31, S ₃₂ , and S _33.
Any one voltage of V ₇ is output as the reference voltage Vref.

By the way, the relationship between the resistance values of the resistors R _{0 to} R ₇ is expressed by the above-mentioned equation, assuming that the resistance value of the resistor R ₀ is 1 KΩ.
From (1), it becomes as shown in the following table. In addition, in the same table, the resistance value of four significant figures is shown.
For example, 90.5Ω → 91Ω, 98.7Ω → 100Ω may be selected. However, in this case, it is necessary to select such that the total sum of the resistances R _{1 to} R ₇ approaches 848 Ω.

Also, for switching the integration capacitor
If the number of bits is multiple, for example 2 bits (S_11,S₁₂)
And in this case four integral condensates
SA C _T1,C_T2,C_T3,C_T4To provide. However, as shown in Figure 1.
In this embodiment, the amount of received light is changed by switching the integration capacitor.
Since it was changed by 2 steps,
Densa C_T1~ C_T4The relationship of each capacity is as shown in the table below.
ItIt should be noted that the amount of light received by the reference voltage Vref
If it is changed within the range, the integration capacitor
Change the amount of light received by one step
You may do it.

[0037]

As described above, according to the automatic light control strobe according to the present invention, the selective switching of the reference voltage and the selective switching of the capacitance of the integrating capacitor are used together, so that the flash discharge tube emits light. Wide adjustable range of quantity,
And it can be finely adjusted. Further, a desired light emission amount can be adjusted by the selection operation (switching operation) based on the strobe light amount setting data of a plurality of bits. Further, it is possible to easily adjust the capacitance error of the plurality of integrating capacitors.

[Brief description of drawings]

FIG. 1 is a principal block diagram showing an embodiment of an automatic light control strobe according to the present invention.

FIG. 2 is a block diagram showing another embodiment of the second voltage switching unit of FIG.

[Explanation of symbols]

10 ... Input terminal 20 ... Emission stop control unit 22 ... First voltage switching unit 24 ... Adjusting unit 26, 40 ... Second voltage switching unit 28 ... Emission amount detecting unit 30 ... Emission unit COMP ... Comparator PT ... Phototransistor _{R 0 ~R 7, R 10 ~R} 11 ... resistance C _T1, C _T2 ... integrating capacitor Xe ... flash discharge tube

Claims (7)

[Claims] 1. An automatic light control strobe for outputting a light emission stop signal to stop light emission from a flash discharge tube when it is detected that an appropriate amount of exposure has been reached based on incident light from a subject. Reference voltage setting means for setting the reference voltage, photoelectric conversion means for outputting a current corresponding to incident light from the subject, a plurality of integrating capacitors each having a different capacity for integrating the current from the photoelectric conversion means, It is possible to select any one of the plurality of reference voltages based on the brightness of the subject and also select any one or more of the plurality of integration capacitors to integrate only the selected integration capacitor. Means for comparing the selected reference voltage with a detection voltage detected by integration in the selected integration capacitor, and the detection voltage is a reference voltage. Automatic light strobe, characterized in that it comprises a comparing means for outputting the light emission stop signal to reach pressure and. 2. An automatic light control strobe for outputting a light emission stop signal to stop light emission from a flash discharge tube when it is detected that an appropriate exposure amount has been reached based on incident light from a subject. Means for generating strobe light amount setting data indicating an appropriate exposure amount consisting of group bits and second group bits based on subject brightness, reference voltage setting means for setting a plurality of reference voltages, and incident light from the subject. , A plurality of integrating capacitors having different capacities for integrating the current from the photoelectric converting unit, and a plurality of the plurality of integrating capacitors based on a first group bit of the strobe light amount setting data. First selecting means for selecting any one of the reference voltages, and a plurality of the integral coordinators based on the second group bit of the strobe light amount setting data. Second selection means for selecting any one or more of the capacitors and allowing only the selected integration capacitor to operate; a reference voltage selected by the first selection means and the second selection Comparing means for comparing with a detection voltage detected by integration in the integration capacitor selected by the means, and for outputting the light emission stop signal when the detection voltage reaches a reference voltage, automatic means comprising: Dimming strobe. 3. The automatic light control strobe according to claim 2, wherein the strobe light amount setting data is EV data having a range of a plurality of steps for equally dividing one step (1EV) in steps of ΔEV. 4. The reference voltage setting means obtains a first setting means for setting a predetermined voltage in two stages of 1 × and 0.5 × by a voltage dividing resistor, and a voltage for dividing 1EV in ΔEV steps. And a second setting means for dividing the applied voltage by a voltage dividing resistor. The first selecting means is set by the first setting means based on one bit of the first group bits. One of the two steps of voltages is selected and applied to the second setting means, and one of the voltages in increments of ΔEV set by the second setting means based on the remaining bits. 4. The automatic light control strobe according to claim 3, wherein is selected. 5. The capacity of any one or a plurality of integration capacitors selected by the second selecting means is 2 ⁿ , ^where C _T1 is an integration capacitor having a minimum capacity among the plurality of integration capacitors. 4. The automatic light control strobe according to claim 3, having a capacity of × C _T1 (n = 0, 1, ...). 6. The capacity of any one or a plurality of integration capacitors selected by the second selecting means is 4 ⁿ , ^where C _T1 is an integration capacitor having a minimum capacity among the plurality of integration capacitors. 5. The automatic light control strobe according to claim 3, which has a capacity of × C _T1 (n = 0, 1, ...). 7. The plurality of variable resistors, each of which is connected in series to the reference voltage setting unit, and the one or more integration capacitors selected by the second selecting unit, according to the plurality of variable resistors. 3. The automatic dimming strobe according to claim 2, further comprising means for selecting any one of the variable resistors and applying a voltage to the reference voltage setting means via the selected variable resistor.