JPH01297635A - Amplification factor switching means of automatic light control device - Google Patents

Abstract

PURPOSE:To control light control aperture values (F values) to multiple stages with fewer switching means by generating signals to change the conduction state of the switching means by a switching control means. CONSTITUTION:The signal to conduct any one of the switching means TR1-TR5 and the signal to conduct any two thereof are generated by the switching control means DEC which changes the amplification factor of a light control circuit by changing the voltage to be impressed to the reference input terminal of an amplifier and the output terminal of an output transistor by selectively conducting the switching means TR1-TR5. The many light control F values are thereby obtd. with the fewer switching means TR1-TR5 and the easily usable light control F values are obtd.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an automatic flash control system that switches the amplification factor of a photometry circuit used for light emission control of an automatic flash control electronic flash device known as an electronic strobe in accordance with an aperture operation. The present invention relates to an amplification factor switching circuit for an apparatus.

[Conventional technology]

Conventionally, in auto-adjustable electronic flash devices used for strobe ↑ darkest, a photometry circuit is used to control the strobe to stop firing when the reflected light from the subject reaches a specified photometry condition. .

That is, the photometry circuit converts the light reflected from the subject due to the light emitted by the flash device into a photocurrent using a light receiving element, and amplifies the converted photocurrent using an amplifier to charge an integrating capacitor. When the amount of charge in this integral capacitor reaches a certain value (reference voltage), it is determined that the appropriate amount of light has been reached and the light emission is stopped.

The dimming control of a flash device using such a photometric circuit is switched according to the aperture value (hereinafter referred to as "F value").
As a method for switching this dimming F value, Japanese Patent Application Laid-Open No. 61-2080
There is a method of changing the amplification factor of the photometric circuit, as disclosed in No. 39.

[Problems to be Solved by the Invention] In such conventional technology, as a method of setting the dimming F value, one of a plurality of switching means (for example, a transistor) connected to a group of resistors is used. is turned on, other switching means are turned off, a constant current is passed from both ends of the resistor group, and the amplification factor of the photometry circuit is set from the voltage difference generated across the resistor group, and the dimming F value is set. .

However, in this method, only one of the plurality of switching means is turned on to set the dimming F value, so switching means are required as many as the number of dimming F values required, and the switching means is not required. The outputs of the control circuit for control are also required for the number of dimming F values.

For this reason, when trying to control the dimming F value in multiple stages, a large number of switching means are required, and the control circuit for controlling the switching means also becomes complicated.

〔Example〕

FIG. 1 shows an embodiment of the invention.

When a power switch (not shown) is turned on, the booster circuit 101 boosts the power source El and charges the main capacitor CI. At the same time, the trigger capacitor C2 is charged via the resistor R5.

Terminals A and B are terminals that are electrically connected to the camera. Terminal A is connected to X contact switch X of the camera.

Further, terminal B is connected to the ground potential of the camera.

When the camera is released and the shutter is fully opened, the X contact switch is closed and terminal A becomes ground potential.
Command the strobe to start firing.

In the strobe, when the terminal A becomes the ground potential, the energy charged in the trigger capacitor C2 is discharged through the primary side of the trigger transformer T.
A high voltage is emitted on the next side to trigger the xenon tube Xe.

As a result, the xenon tube Xe consumes the energy charged in the main capacitor CI to emit flash light.

When a stop signal is input to the input of the dimmer circuit 102 while the xenon tube Xe is emitting light, the dimmer circuit 102 rapidly discharges the charging energy of the main capacitor CI and stops the xenon tube Xe from emitting light.

Next, the photometric circuit portion according to this embodiment will be explained.

103 is an IC, a decoder DEC converts the serial signals input from inputs C and D, and outputs E, F, G, H.
, I, and J.

Outputs E, F, G, HS I are transistors TRI~T
It is an open collector by R5, and the output state is selected as "LO" or open.

Further, these transistors are formed in the IC with the same size. It is known that transistors formed in the same size in an IC have the same electrical characteristics such as hfc.
When the same current is applied to the collectors of RI to TR5 and the transistors are turned on, the saturation voltage (collector
It can be seen that the emitter-to-emitter voltages are all the same voltage.

In addition, the output J is set to “HT” or “ from the decoder DEC.
LO” is output.

The connection points of the resistor groups R6, R7, R8, R9, RIO, and R11 are connected to the IC outputs E, F, G, and I, respectively.
■ is connected. A constant current of 1. ．． 1. is flowing in, and the output E of the IC is
~■ One or more of them are "LO", and 1. ．． Since 1□ flows, a voltage is generated across the resistor group. This voltage is the op amp OPI
, op amp OP2 due to the voltage buffer by OP3
The "+" input of the photometric amplifier is applied to the emitter of the logarithmic stretching transistor TR8.

The photometric system consisting of a photometric amplifier and logarithmic expansion includes a photodetector D2.
As described later, the photoelectrically converted current is amplified by an amplification factor determined by the voltage applied to the photometric system,
Output to the collector of transistor TR8.

A capacitor C3 is connected to the collector of the transistor TR8.
, C4 are connected.

A transistor TR7 is connected to the other end of the capacitor C4, and TR7 is ON/OFF controlled by the output J of the IC103. When the output of the output J of IC103 is Hr'', TR7 is turned off, so the connection of the capacitor C4 is cut off, and the only capacitance connected to the collector of the transistor TR8 is the capacitor C3. When the output of output J is "LO" - Transistor TR7 is ONL, 0 in parallel to capacitor C3
The capacitance connected to the collector of the transistor TR8 is the parallel combined capacitance of the capacitors C3 and C4, that is, the capacitance of C3+C4.

On the other hand, before the strobe emits a flash, the transistor TRLO is OFF as described above, and the transistor TR9 is ON because current is supplied to its base from the power source E1 through the resistor R2. As a result, the base current of the transistor TR6 is increased by the resistor R1.
Since the current flows to transistor TR9 via
It's on.

When transistor TR6 is ON, transistor T
The collector of R8 becomes the voltage of the power source E1, and the capacitor C3 is short-circuited, and the electric charge charged in C3 is discharged. Further, even if an output is output from the transistor TR8, it is not charged.

The output J of IC103 is ``LO'' and the transistor TR7 is ``O''.
Even in the state of N, the charge of capacitor C4 is T
Since R7 is ON, as is well known, current flows in the opposite direction from the collector to the emitter, causing discharge.

When the strobe starts flashing, a light emitting current is generated,
The light emission voltage flows through the resistor R3 and turns on the transistor TR10.
Therefore, the base of transistor TR9 is shorted, TR9 becomes 0FFL, and at the same time, transistor TR6 also becomes 0FFL.
FF.

The flash light illuminates the subject, and the reflected light is reflected by the light receiving element D.
2 is photoelectrically converted. This photoelectrically converted current is amplified by the photometric system and output from the collector of the transistor TR8.

This charges the capacitor C3 or the parallel circuit of capacitors C3 and 04.

When the amount of charge reaches the reference voltage E2, the output of the comparator COM is inverted and a stop signal is output to the dimming circuit 102, which causes the discharge tube Xe to stop emitting light, resulting in an appropriate light amount. The light control circuit 102 is a parallel control light control circuit that instantly discharges the remaining charge stored in the main capacitor C1 and interrupts the light emission of the discharge tube Xe.

In the first embodiment, a parallel control method is used as the dimming method, but the dimming circuit may be a well-known series method.

The switching of the dimming F value will be described below.

First, the amplification factor switching method of the photometry system will be described. To simplify the explanation, transistor TR7 is
The explanation will be given under the condition that the transistor TR8 is in a state where the capacitor C3 is the only capacitor connected to the collector of the transistor TR8.

The amplification factor of the photometric system consisting of operational amplifier OP2 and transistor TR8 is determined by the F applied to the “+” input of operational amplifier OP2.
The photocurrent T[ of the photodetector D2, the charging current of the capacitor C3, is uniquely determined by the voltage difference (V, -V.) between the voltage at point ■, and the voltage V8 at point E applied to the emitter of the transistor TR8. ■. Then, the relationship between the input current 1g and the output current IC is expressed by the following equation (3).

In other words, the output voltage V, (base potential of TR8) of the operational amplifier OP2 is logarithmically compressed by the light receiving current z,2 by the logarithmic compression diode D2, K: Boltzmann constant T: Absolute temperature q: Electron charge I8: Opposite direction of diode D2 This becomes a saturation current.

The transistor TR8 is a logarithmic expansion means, and a collector current, which is an output thereof, flows to the emitter, thereby generating a base-emitter voltage.

At this time, the base voltage of TR8 is the same as the above V, and 1,': ) Reverse saturation current of the base-emitter diode of Lancistor TR8 (1), (2). , IS' is a diode and transistor of the same size made in the same IC chip, then T, = 1. ', so (1), (
From equation 2), Therefore, if the value of (vr-v,) is made proportional to the absolute temperature T, the output current of this photometric system becomes <vr-v,
Setting > means that it is constant regardless of temperature.

As is clear from this equation (3), in order to switch the dimming F value, the reference voltage V, and ■. All you have to do is change the voltage difference (sir-V-) between the two. In other words, switching the dimming F value to one step open side means doubling the amplification factor, and at this time, the charging current is increased so that the voltage at point E is v, I, and the voltage at point F is , then it follows from the above equation (3), and rearranging this, we get the following. Therefore, taking the natural logarithm of this equation, Io2=(
(Vr+V-+) (VrV,) ). Furthermore, to summarize the fluctuation of the voltage difference between point F and point E, T 'n2= (Vr+ V-+) (Vr V
−). Here, T is the absolute temperature, q is the elementary charge, and q=l.

60X10-19, k is Portzmann's constant = 1°38
X10-”, so when calculated at an ambient temperature of 25°C, (Vv+ V-+) (Vr V,) = 0
．． 0178 (V). Therefore, when switching the dimming F value to the open side by one step, it is sufficient to increase the voltage difference (Vr ve) between point F and point E by 17.8 mV compared to before opening.

T Similarly, it goes without saying that in order to increase the amplification factor by N times, a potential difference of □1nNmV can be added to V and -V.

If we consider the amplification factor when only the output G of IC103 is "LO" (only transistor TR3 is ON), the voltage Vf at point F is the sum of the current 11 flowing through resistors R6, R7, and R8 and the voltage of transistor TR3. Saturation voltage ■T
0, Vy = 11
It becomes TR3, and the voltage difference is V, -V. is V, -V, = It x (R6+R7+R8) -
Iz X (R9+R10+R11), and the saturation voltage VTR3 is ignored.

At this time, the amplification factor is 1 c / I (2), and it can be seen that it varies depending on the temperature.

Therefore, as mentioned earlier, if the constant current 1+ and It are an absolute temperature proportional constant current source whose constant current output varies in proportion to the absolute temperature (T), then the constant current Il, ■2 becomes It = AIT
, Iz = AzT (At, Az are constants), and from this formula, the amplification factor is 2 (AtT
X (R9+R10+R11))■c/■P=eKT -(Δ+X (R6+R7+R8)-8z X (R
9+R10+R11)1k, and fluctuations due to temperature can be prevented.

Next, we will discuss switching the dimming F value. First, resistor R
6 to R11 are all set to the same resistance value R, and a constant current of 1. ,I2
If the current value is the same, only the output G mentioned above is “LO”.
The voltage difference when Lr Ve −I X (R+R
+R) I X (R+R+R) = 0.

(The gain of the photometric amplifier is 1) Next, only the two outputs G and H of IC103 are “LO” and the others are open (TR
3. The state where TR4 is ON and TR1TR2 and TR5 are 0FF will be described.

The voltage difference at this time is: The voltage Vf at point F is determined by the constant current flowing through resistors R6, R7, and R8 and the saturation voltage of transistor TR3 A R8, and becomes Vl = I X (R+R+R) +VTR3, and point E The voltage ■ is the constant current flowing through the resistor RIO1R11 and the saturation voltage V of the transistor TR4.
Determined by TR4 ■. = IX(R+R)+V? l
14, Vr-V, = 3 1XR+VTII+-(2IXR+
V? R4) ------(21).

1+, It have the same current value, and the transistor TR3
Since TR4 and TR4 are transistors formed in the same IC with the same size, they have the same electrical characteristics as described above.

Therefore, if the current value flowing between the collector and emitter is the same, the saturation voltage of the transistors will also be the same, and VTR3=VT.

As a result, the voltage difference equation (2) is: Vr　V,=31XR2TxR=IxR.

As can be seen from the above, the voltage difference between point F and point E becomes maximum when only output I becomes "LO", and the voltage difference at that time is V, -V. =41R The minimum value is the output E
Voltage difference V, -V, = -41 when only becomes "LO"
It becomes R.

Further, the relationship between the output state of the output E-1 of the IC 103 and the voltage difference is as shown in FIG. 2, and nine types of voltage differences, that is, dimming F values can be obtained.

Further, when adjusting the amplification factor of the photometric system in this embodiment, by changing the constant current I+ and ItO value, it is possible to change the variation IR in the voltage difference due to a change in the state of the output E-1.

For example, if this variation in IR is equivalent to one step (=2 times) of the dimming F value, then it is necessary to adjust It and Iz so that IR=17.8 mV<, 2/3 steps (=1.59 If the voltage is doubled), it is sufficient to adjust It and Iz so that I R = 17.8 X2/3 = 11.9 mV.

Furthermore, in order to adjust the exposure amount by increasing or decreasing the light emission amount of the overall light control F value, for example, resistor R11 or R6
may be made into a variable resistance.

For example, if R11 is a variable resistor and R' is an adjustable resistor of the variable resistor, the resistance value at that time can be expressed as R11 = R + R', and when only the output JG is "LO", the amplification factor is becomes.

When only the two outputs G, , and H are "LO", the amplification factor increases, and by adjusting the variable portion R' of the variable resistor, it is possible to increase the amount of light emitted during dimming. Become.

Furthermore, it is clear that the resistor R6 is similarly a variable resistor, R6=R+R'.

As described above, in this embodiment, it is possible to obtain a large number of dimming F values with a small number of switching means, such as being able to obtain nine types of dimming F values simply by connecting five outputs to a resistor group. Therefore, the number of switching means can be reduced, and the control means for controlling the switching means, the decoder DEC in this embodiment, does not become complicated.

Next, as a method for further increasing the dimming F value, a method will be described in which the transistor TR7 is turned on and off to increase and decrease the capacitance connected to the collector of the transistor TR8. As described above, this photometric circuit outputs a stop signal when the capacitor connected to the collector of the transistor TR8 is charged with a charge equal to or higher than the reference voltage E2. The calculation formula representing this charging voltage is based on the well-known fact that as the capacitance C increases, the charging current i required to reach the reference voltage E2 increases.

From the above, it can be seen that by turning on the transistor TR7 and adding the capacitor C4 to the collector of the transistor TR8, the amount of light emitted by the strobe increases until the photometry circuit outputs the stop signal.

In other words, adding the capacitor C4 shifts the dimming F value to the small aperture side. (The amount of light emitted increases and proper exposure is achieved with a small aperture.) For example, when switching the amplification factor of the photometry system, IR = 11.9 m
V, so that the dimming F value can be obtained every 273 steps,
If the light amount is increased by 173 steps by adding the capacitor C4, 18 types of dimming F values can be obtained as shown in FIG.

FIG. 4 shows how the dimming F value was determined using this.

This is a method in which the dimming F value is determined for each step for each ISO value. Conventionally, the dimming F value has been determined for 15O100. For example, at 15O100, set the dimming F value to R
If it is set to 4, the ISO sensitivity will be one step higher, that is, l5O20.
If it is set to 0, the aperture can be shifted to the small aperture side by that amount, resulting in a light control F value of F5.6. On the other hand, the aperture of a photographic lens is usually divided into steps, and each step has a click, making it easier to locate the aperture. However, on the other hand, it is difficult to find the intermediate position of the aperture. However, as mentioned above, when the light control F value is 15O100 and R4, the ISO sensitivity is 80 or 125.
If the sensitivity is intermediate, such as R4, R5, 6, etc., the dimming F value is also 1.
The values will be intermediate values instead of values for each stage.

For example, for l5O80, the dimming F value must be shifted to R4-173 steps, that is, 173 steps more open than R4, and for l5O125, the dimming F value is F4 + 1/3 steps, that is, 173 steps smaller than F4. must be shifted to the side. However, as mentioned above, the photographic lens has
It is difficult to set the aperture every 173 steps, and the
At sensitivities such as 80 and 125, it was difficult to match the aperture of the photographic lens to the light control F value.

Therefore, as in this embodiment, the light control F value is provided in multiple stages, and the fourth
At the bottom of the table in the figure, the ISO sensitivity is divided into 173 steps.

When 15O100, an output corresponding to the F value of group B is output to output EJ of IC103.

When l5O80, the output of IC103 is calculated from the F value of group A, and when l5O125, the output of IC103 is calculated from the F value of group 0.
Output to J. As a result, when the ISO sensitivity is in steps of 150 to 100, you can choose from the B group, and at other intermediate sensitivities, choose from the A or 0 groups. It is possible to obtain the light control F value for each stage of aperture value.

In addition, even if it is possible to obtain the light control F value for each step of aperture at any sensitivity, as shown in Figure 4, the l50
100 is compatible with almost all apertures such as F2.2.8.4.5.6.8.11.

In addition, if you set a value different from the ISO sensitivity of the film you are using, 17
There is also the advantage that exposure compensation can be applied every three steps.

For example, if you use film with an ISO sensitivity of 100 and try to correct the light intensity by 173 steps, the I
If the SO sensitivity is set to 80, the set dimming F value will be l5.
It can be seen that the light emission amount is controlled so that the light amount exceeds O100 by 173 steps, and a correction of 173 steps is applied.

As described above, according to the present embodiment, it is possible to obtain a dimming F value as many as the number of switches using a small number of switching means, and thereby it is possible to obtain a dimming F value that is easier to use.

Although transistors are used as switching means in the embodiments, similar effects can be obtained by using other semiconductor switching means such as FETs.

Further, although a transistor within the same IC is used as the switching means, the same effect can be obtained even if a separate switching means such as a transistor or FET having the same electrical characteristics is used.

Further, even if a switching means other than a semiconductor is used, such as a mechanical slide switch, the same effect can be obtained as long as the voltage drop caused by the contact resistance can be sufficiently ignored.

[Brief explanation of the drawing]

FIG. 1 shows an embodiment of the amplification factor switching circuit according to the present invention, and FIG. 2 shows the relationship between the output state of the output terminal E-1 and the voltage difference (V, -V.) in FIG. Figure 3 shows the relationship between the output state of the output terminal E-J and the level difference (EV) of the dimming F value, and Figure 4 shows the relationship between the output state of the output terminal E-J and the level difference (EV) of the dimming F value. It shows the relationship between the output state and the dimming F value corresponding to each ISO value ABC. [Explanation of symbols of main parts] D2--light receiving element, OPI, OP2.0P3- operational amplifier, C3, C4--
- Integrating capacitor, TR6, TR7, TR8... - Transistor, COM'
---Comparator, R6, R7, R8, R9, RIO, R11--Resistance, D
E C-control means. Figure 2 Broom Figure 5

Claims (1)

[Claims] A light receiving element (D2) that receives reflected light from an object, and amplifiers D1 and OP1 that amplify the photocurrent (I_l) of the light receiving element.
OP2, OP3, TR8), an integrating capacitor (C3, C4) that starts charging by flash light emission, an output transistor (TR8) that controls the charging current of the integrating capacitor by the output of the amplifier, and a A light emission stop circuit (CO
M) has a dimming circuit consisting of a voltage applied to the input terminal (point F) of the amplifier and the output side of the transistor (
An amplification factor switching circuit for an automatic dimming device that switches the amplification factor of the dimming circuit based on the voltage difference between the voltage applied to the voltage applied to the point a resistor section (R6 to R11) whose other end is connected to the reference input terminal of the output transistor, and two constant current sources (I_1) connected to both ends of the resistor section, respectively.
, 1_2), and a plurality of switching means (T
R1 to TR5) and the switching means are selectively made conductive to change the voltage applied to the reference input terminal of the amplifier and the output terminal of the output transistor, thereby switching the amplification factor of the dimming circuit. Control means (
In the amplification factor switching circuit for an automatic light control device having a DEC), the switching control means may transmit a first signal that makes any one of the switching means conductive, and a second signal that makes any two of the switching means conductive. An amplification factor switching circuit for an automatic light control device characterized in that: