JPH03235932A - Emission quantity controller for electronic flash - Google Patents

Abstract

PURPOSE:To control the quantity of emission with sufficient accuracy even when a general purpose D/A converter is used by stopping the emission of an electronic flash corresponding to the result of comparison between the output voltage of a light quantity detecting means and a threshold value. CONSTITUTION:A voltage TTLout corresponding to the quantity of the emission of the electronic flash 15 is inputted to the negative input terminal of a comparator 30 and the threshold value which is set through the D/A converter 40 is inputted to the positive input terminal. While a TTL amplifier starts integration and a photodetector senses the light, the TTLout is decreased monotonously with the lapse of time. When the voltage TTLout becomes less than the threshold value, a comparator 30 changes from low to high to output an emission stopping signal. A CPU 20 controls a driving circuit 23 corresponding to the emission stopping signal to stop the emission of the electronic flash 15. Consequently, even when the general purpose D/A converter is used, the quantity of emission can be controlled with sufficient accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a device for controlling the amount of light emitted from a camera flash according to film sensitivity.

[Conventional technology]

The TTL flash 8-round light system detects the amount of light emitted by the flash via a light receiving element provided in the camera body, and controls the flash to stop emitting light when the detection circuit detects a predetermined amount of light. That is, in this system, the output voltage of the TTL amplifier of the detection circuit decreases while the flash is emitting light, as shown in FIG. The threshold value (TH
), the flash will stop firing. This threshold value is determined according to the film sensitivity and exposure multiple; the higher the film sensitivity, etc. be done.

However, as the film sensitivity increases, the threshold value increases and becomes too close to the reference voltage, which is the initial value of the output voltage of the TTL amplifier, and the resolution of the TTL dimming level decreases. For this reason, conventionally, when the film sensitivity exceeds a certain value, the gain of the TTL amplifier is increased (5th
The slope of the solid line S in the figure is increased), the threshold value is lowered, and the dimming level is adjusted.

[Problem to be solved by the invention]

Here, there is no problem if a D/A converter for setting the threshold value that covers only the output voltage of the TTL amplifier is used.

However, when this D/A converter is shared with something other than a dimming system, the output voltage range of this D/A converter is T
Since the output voltage range of the TL amplifier is exceeded, the resolution for setting the threshold value decreases, and simply increasing the gain of the TTL amplifier and lowering the threshold value as in the past makes it difficult to control the amount of light emitted with sufficient accuracy. The problem arises that it cannot be controlled.

An object of the present invention is to provide a device that can control the amount of light emitted with sufficient accuracy even when a general-purpose D/A converter is used.

[Means to solve the problem]

A flash light emission amount control device according to the present invention includes a light amount detection means that outputs a voltage that changes over time while a light receiving element senses light, an output voltage of a D/A converter, and a D/A converter.
threshold setting means capable of selectively setting one of the output voltage of the converter and the voltage obtained by dividing the constant voltage as a threshold value; and the output voltage of the light amount detection means and the threshold value. The present invention is characterized in that it includes a comparison circuit that outputs a signal according to the comparison result between the two and a means for stopping the emission of the flash according to the signal.

〔Example〕

The present invention will be explained below with reference to illustrated embodiments.

FIG. 2 shows an example of the configuration of the optical system. In this figure, a light receiving lens 1 is located between the photographing lens 11 and the film surface 12.
3 and a light-receiving element 14 are provided, and the light-receiving element 14 receives, via the light-receiving lens 13, the light that has passed through the photographing lens 11 and reflected on the film surface 12. The amount of light emitted by the flash 15 is detected by a TTL dimming circuit including the light receiving element 14, and when the amount of light emitted reaches a predetermined value, the light emission of the flash is stopped. In the present invention, the flash 15 may be built into the camera body or may be externally attached.

3-1 Figure 1 shows the configuration of a TTL optical circuit. The various basic controls of this circuit are controlled by a microcomputer (C
PU) 20. A film sensitivity setting section 21 and an exposure multiple setting section 22 are connected to the CPU 20 . The film sensitivity setting section 21 reads the ISO sensitivity (Sv) of the film from, for example, the DX code of the film cartridge, but may also manually set the ISO sensitivity.

The exposure multiple setting unit 22 is a switch provided on the camera body to set the exposure multiple (Xv).

A drive circuit 23 for controlling the flash 15 is connected to the CPU 20, and an E"F for storing various information is connected to the CPU 20.
ROM24 is connected.

A voltage TTLout corresponding to the amount of light emitted by the flash 15 is input to the negative input terminal of the comparator 30, and a threshold value set via the D/A converter 4o is input to the positive input terminal. be done.

As will be described later, the voltage TTLout monotonically decreases with the open time during which the TTL amplifier starts integration and the light receiving element 14 is sensing light. The comparator 30 has a voltage TTLou
“Low” when t becomes smaller than the threshold value
becomes "high" and outputs a light emission stop signal. CPU
20 controls the drive circuit 23 in response to this light emission stop signal to stop the flash 15 from emitting light.

The integrating circuit, that is, the TTL amplifier that outputs the voltage TTLout according to the amount of light emitted by the flash, is operated by the operational amplifier 31.
, capacitor 32, resistor 33, 34 and switch 35
．． It has 36.37. A light receiving element 14 is connected to each input terminal of the operational amplifier 31. Further, a reference voltage generation circuit having a resistor 51, 52 and a buffer 53 is connected to the positive input terminal of the operational amplifier 31, and a reference voltage Vsl is inputted from this circuit. The start switch 35 is closed by the CPU 20 at the start of measuring the amount of light emitted,
As a result, the output voltage TTLout of the integrating circuit monotonically decreases from the reference voltage Vsl toward 0.

TTL gain switches 36 and 37 are used to set the gain of the integrating circuit, that is, the TTL gain. Resistance 33.
The resistance value of 34 is a ratio of 1:3.

Therefore, switch 36 is ON and switch 37 is OFF.
When , the TTL gain is 1 times, and when the switch 36 is OFF and the switch 37 is ON, the TTL gain is 4 times. ON-OFF control of these switches 36 and 37 is performed by the CPU 20.

A threshold setting circuit that sets a threshold value input to the comparator 30 is an 8-bit D/A converter 4.
0, a buffer 41, resistors 42 and 43, and a D/A gain switch 44. The D/A converter 40 is a constant voltage source V
ref (for example, 4V), and a constant voltage Vr
ef is F, S, (full scale) of this D/A converter 40. The D/A converter 40 also generates a digital signal (8 bits) corresponding to the Sv correction value (5VTTL in FIG. 7) determined by the sum of the film sensitivity and the exposure multiple.
is input from the CPU 20, and an output voltage VD/A corresponding to this Sv correction value is output. Here, Sv correction value (SVT
When the digital input value corresponding to TL is n, the output voltage VD/^ becomes VD/A = (n/255) ·Vref.

The resistor 42 is connected to the D/A converter 40 via a buffer 41, and the resistor 43 is connected via a switch 44 to a buffer 53 of the reference voltage generation circuit.

The switch 44 is operated by the CPU 20 as described below.
ON-OFF control is performed according to the v correction value.

When this switch 44 is in the OFF state, the D/A converter 40
The output voltage of the D/A converter 40 is directly input to the comparator 30, and when it is in the ON state, the voltage obtained by dividing the output voltage of the D/A converter 40 and the reference voltage Vsl is input to the comparator 30. resistance 4
A resistance value of 2.43 is a 3 to 1 ratio. Specifically, when the switch 44 is in the OFF state, the positive input voltage range of the comparator 30 is 0 to Vref (V), and the switch 44 is in the OFF state.
is ON, (3/4)νsl ~ 1/4(V
ref+3Vsl) (V), and the switch 44 is turned on.
The positive input voltage width of the comparator 30 in the state is (1/4)
Vref, and is compressed to 1/4 compared to when the switch 44 is in the OFF state. Therefore, the gain due to this threshold setting circuit, that is, the D/A gain, is 1 times when the switch 44 is in the OFF state, and when the switch 44 is in the ON state.
It is 1/4 times the state.

The resistance values of the resistors 51 and 52 of the reference voltage generation circuit have a ratio of 1:3, and the reference voltage generation circuit has a constant voltage source Vref (4
The reference voltage V for the TTL amplifier is obtained by resistor division from V).
sH3V).

Figure 3 shows the CPU 20, start switch 35, and TT.
The connection relationship with the L gain switches 36, 37, the D/A gain switch 44, etc. is shown. The start switch and each TTL gain switch 35, 36, 37 are
A signal is input from the internal bus 61 of the CPU 20 via the latch circuit 62 and the logic circuit, and is turned on and off at a predetermined timing. The D/A converter 40 receives a digital value corresponding to the Sv correction value from the bus 61 via the latch circuit 63, converts it into a D/A, and outputs it to the comparator 30. C
The PU 20 is connected to the D/A gain switch 44 via a latch circuit 64 to turn it on and off. Also CPU
The FQ terminal 20 is connected to the flash 15 and outputs a light emission stop signal to stop the flash 15 from emitting light.

FIG. 4 shows a routine executed when adjusting the TTL dimming circuit. This routine determines coefficients for correcting variations in performance of the dimming circuit, and these correction coefficients are used in the TTL flash processing routine shown in FIG.

In step 61, the reference voltage Vsl (3 V) is read into the CPU from a circuit (not shown) and A/D converted. This A/D converted value is stored in the E''FROM 24 as Eo in step 62. In step 63, light having a constant amount of light is applied to the light receiving element 14, and integration by the integrating circuit is started.

As a result, the output from the integrating circuit (TTL amplifier) decreases as shown by the solid line S in FIG. In step 64, a timer counts the time since the integration started. In this step 64, the output value of the integrating circuit reaches the threshold value TI corresponding to the above-mentioned constant light amount, and in step 65, the output signal of the comparator 30 is r
This is repeated until it reaches High J, and thereby the time Tx until the output value of the integrating circuit reaches the threshold value TH is measured. In step 66, the correction coefficient Ha(-To/Tx)
is calculated. The output of this integrator circuit is designed to decrease as indicated by the broken line J and reach the threshold TH at time To for the above-mentioned constant light amount. By using this correction coefficient Ea, each TTL The dimming circuit is now able to cause the flash to emit light for a period of time To (step 75 in FIG. 6). In step 67, the correction coefficient Ea is stored in the E''PROM24.

FIG. 6 shows a TTL flash processing routine, which is executed during actual photographing, for example, at the time of shutter release.

In step 71, the reference value EO is read from the E''PROM 24, and in step 72, the correction coefficient Ha is read from the E''PROM24. In step 73, the sum of the film sensitivity Sv and the exposure multiple Xv, that is, the Sv correction value 5
VTTL is required. Here, it is assumed that the film sensitivity Sv and the exposure multiple Xv have been read in advance from the film sensitivity setting section 21 and the exposure multiple setting section 22 at the time of photometry calculation.

In step 74, table 130 (not shown in FIG. 7) is referred to, and the r D/A step corresponding to rSVTTL J is
is loaded.

The ISO table shows the relationship between the Sv correction value 5VTTL and the D/A step. Ite to this table, 'TTL L/) I/J is SO (7) rSVTT
The potential difference (mV) between the reference voltage νs1 at L J and the threshold value, that is, the threshold value should be set at how many mV the output voltage of the TTL amplifier has decreased from the reference voltage Vsl. Further, "r D/A step" is a D/A converter setting conversion value of "r TTL level", and rlsOJ indicates film sensitivity.

Now, in step 75, based on the reference value EO1 correction coefficient Ea and the D/A step X, digital data to be output to the D/A converter 20 in the currently used dimming circuit is calculated.

In step 81, it is determined whether the film sensitivity (ISO) is greater than 200. If the film sensitivity (■ = 11 = 12 SO) is less than 200, in step 82 the TT
If L gain is set to 1x and greater than 200,
In step 83, the TTL gain is set to 4 times. If the film speed (150) is 200 or less, in step 84, the film speed (ISO) is further set to 50.
If it is 50 or less, the D/A gain is set to 1 in step 85, and if it is greater than 50, the D/A gain is set to 1 in step 86.
It is set to 4 times. On the other hand, if it is determined in step 81 that the film sensitivity (ISO) is greater than 200, after execution of step 83, in step 86 the D/A
The gain is set to 1/4.

The processing contents of steps 81 to 86 will be explained again with reference to FIGS. 1 and 7.

When the film sensitivity (ISO) is 50 or less, the TTL gain switch 36 is in the ON state, and the TTL gain switch 37 is in the ON state.
is in the OFF state, and the D/A gain switch 44 is also OFF.
determined by the state. Therefore, the TTL gain is 1x,
The D/A gain is 1x.

Further, when the film sensitivity (150) is between 50 and 200, the TTL gain switch 36 is set to the ON state, the TTL gain switch 37 is set to the OFF state, and the D/A gain switch 44 is set to the ON state. Therefore, the TTL gain is 1 times and the D/A gain is 1/4 times. When the film sensitivity (ISO) is greater than 200, the TTL gain switch 36 is in the OFF state, and the TTL gain switch 37 is in the OFF state.
is set to the ON state, and the D/A gain switch 44 is set to the ON state. Therefore, the TTL gain is 4x, D/
A gain is 1/4.

In FIG. 6, in step 91, the flash starts emitting light via the drive circuit 23, the start switch 35 is closed, the integration of the integrating circuit is started, and the measurement of the amount of light emitted by the flash is started. After a predetermined waiting time is provided in step 92 to prevent noise generation, a quench (Q) permission signal is output in step 93, thereby making it possible to stop the flash 15.

As mentioned above, the flash stops emitting light when the output type 3 4 pressure of the integrating circuit becomes smaller than the threshold value.

Next, the operation of the TTL flash light control system in this embodiment will be explained with reference to FIGS. 3 and 8.

First, with reference to the table in FIG. 7, the "r D/A step according to rSVTTL J" is read, and the reference value Eo and correction coefficient Ea are applied thereto to determine the threshold value TH (see FIG. 6). step 75). The TTL gain is then set based on the film sensitivity. A control signal for setting the TTL gain is output from a predetermined line of the bus 61 within the CPU 20, as shown in FIG. The TTL gain is set to 1 when this control signal is "engine", and is set to 4 times when this control signal is "0". TT
After setting the L gain, the D/A gain is set based on the film sensitivity. A control signal for setting the D/A gain is also output from a predetermined line of the bus 61.
The gain is set to 1/4 when this control signal is "1", and is set to 1x when this control signal is "0".

After setting the TTL gain and A/D gain,
An integration start signal is outputted via a predetermined line of the bus 61, the start switch 35 is opened, and either the TTL gain switch 36 or 37 is closed, and the measurement of the amount of light, that is, the integration by the integration circuit is started. At approximately the same time, the flash starts emitting light, and the output voltage TTLOUT of the integrating circuit monotonically decreases from the reference voltage Vsl.

After the integration start signal is output, a quench (Q) permission signal is output from a predetermined line of the bus 61, allowing the flash to stop emitting light. And the output voltage TT of the integrating circuit
When LOUT becomes smaller than the threshold value TI,
The output signal of the comparator 30 is inverted from "Lj to rH," and the quench signal changes from "L" to "r" (J. Since the CPU 20 is provided with an R-S flip-flop 65, the quench signal is not affected by this chattering.
- 16- In response to the change of the signal to "H", the CPU 20 (7) FQ
The terminal changes from the OFF state to the ON state, thereby quenching the flash 15 and stopping light emission.

FIG. 9 shows a temporal change in the output voltage TTLOIIT of the integrating circuit with respect to ISO during flash emission.

When the film sensitivity (ISO) is between 25 and 200, the TTL gain is set to 1. Therefore T
The output voltage of the TL amplifier is from the reference voltage Vs1 to the broken line Z1.
and decreases along solid line Z2.

If the film sensitivity (rso) is 25, the threshold value is set 1200 (mv) below the reference voltage, and the flash emission is stopped after a time TI from the start. Similarly, if the film sensitivity (ISO) is 50, the threshold value is set 600 (mv) below the reference voltage, and the flash fires at a time TZ
(Half of TI) after which it is stopped.

When the film sensitivity (ISO) is between 25 and 50, the D/A gain is 1x;
O) is between 50 and 200, the D/A gain is 1
/4 times. In other words, the film sensitivity (ISO) is 50.
to 200, the output voltage of the D/A converter 40 changes in the range of 2.25V to 3.25V, and the accuracy of setting the threshold value is increased.

On the other hand, when the film sensitivity (ISO) becomes larger than 200, the TTL gain is set to 4 times, and the output voltage of the TTL amplifier decreases along the solid line Z3.

Also, the D/A gain is set to 174 times, so the setting accuracy of the threshold value is based on the film sensitivity (ISO).
is in the range of 50 to 200.

In this way, according to this embodiment, even if the D/A converter 40 is a general-purpose one and has a wide output voltage range, the resolution of setting the threshold value can be improved, and the amount of light emitted by the flash can be reduced. It can be controlled with high precision. In addition, this embodiment is configured to obtain changes in D/A gain by dividing the voltage by resistors 42 and 43, so the influence of noise is reduced = 17 8 and the amount of light emitted by the flash can be controlled with high precision. Is possible. Furthermore, in this embodiment, by setting the D/A gain to, for example, 1/4, the dimming range can be expanded compared to the conventional one, and even if the film sensitivity (150) is 800 or more, the predetermined accuracy can be maintained. It is possible to dim the light.

〔Effect of the invention〕

As described above, according to the present invention, even when a general-purpose D/A converter is used, the amount of light emission can be controlled with sufficient accuracy.

[Brief explanation of drawings]

Figure 1 is a circuit diagram of the TTL dimming circuit, Figure 2 is a perspective view of an example of a camera optical system, Figure 3 is a circuit diagram of the microcomputer and its surroundings, and Figure 4 is a flowchart of the adjustment routine. , Figure 5 is TT
Figure 6 is a flowchart of the TTL flash processing routine; Figure 7 is an ISO table; Figure 8 is a diagram showing the flash dimming control operation; FIG. 9 is a diagram showing changes in the output voltage of the TTL amplifier. 14... Light receiving element 36.37... TTL gain switch 44... A/
D gain switch

Claims (1)

[Claims] (1) While the light-receiving element detects light, a light amount detection means that outputs a voltage that changes over time, the output voltage of the D/A converter, and the output voltage of the D/A converter and a constant voltage are divided. threshold setting means that can selectively set one of the voltages obtained by the threshold value as a threshold value; and outputting a signal according to a comparison result between the output voltage of the light amount detection means and the threshold value. A flash light emission amount control device comprising a comparison circuit and means for stopping flash light emission in accordance with the signal.