JPH0438337Y2 - - Google Patents

Description

[Detailed explanation of the idea]

This invention relates to an automatic light control signal circuit included in a flash discharge light emitting device for photography having an automatic light control function. As is widely known, a flash discharge light emitting device with an automatic light control function has a function that automatically determines the amount of light emitted according to the light reflected from the subject. The device includes an automatic dimming signal circuit that generates a dimming signal, and a light emission stop circuit that receives the dimming signal and stops the flash discharge tube from emitting light. The automatic light control signal circuit for this type of flash discharge light emitter includes a photoelectric converter that receives reflected light from the subject and converts it into electricity, an integrator that integrates the photoelectric conversion signal, and an integrator that integrates the photoelectric conversion signal until the integrated value reaches a predetermined value. Many of them consist of switching circuits that operate when the FIG. 1 is a circuit diagram showing a typical conventional example of a flash discharge light emitter with an automatic dimming function. In this figure, 1 boosts the low voltage of a battery power source 2 to charge a main discharge capacitor 3. DC-DC converter,
4 is a power switch, and 5 is a trigger circuit that applies an excitation voltage to the flash discharge tube 7 when the trigger switch 6 is closed. 8 is an SCR as a main switching member, and this SCR 8 forms a light emission stop circuit with a commutating capacitor 9 and an SCR 10 as a sub-switching member. Incidentally, the series circuit of the capacitor 11 and the resistor 12 is a starting circuit that applies a gate voltage to the SCR 8. Reference numeral 13 denotes a phototransistor forming a photoelectric converter, and this phototransistor 13 forms an automatic dimming signal circuit with a capacitor 14 as an integrator and a switching circuit 15. In the flash discharge light emitting device circuit described above, when the flash discharge tube 7 emits a flash light as is well known, the reflected light from the object enters the photo transistor 13 and is photoelectrically converted. The photoelectrically converted electric signal is then integrated by the capacitor 14, and when this integrated value reaches a predetermined value, the switching circuit 15 operates and supplies a gate voltage to the SCR 10. When SCR10 receives gate voltage and becomes conductive,
Since the charging voltage of the commutating capacitor 9 is applied as a reverse voltage between the anode and cathode of the SCR 8, this
The SCR 8 becomes non-conductive and the flash discharge tube 7 stops emitting flash light. FIG. 2 roughly shows the point at which the flash discharge tube 7 stops emitting light, the amount of light emitted from which is controlled as described above.
6, 17, and 18 are reflected light curves when the subject is located at a short distance, a middle distance, and a long distance. In this figure, the horizontal axis represents time, and the vertical axis represents the intensity of light reflected from the object. As can be seen from this figure, if the subject is located at a short distance, the flash light emission will be stopped after the time Ta has elapsed, and similarly, if the subject is located at a medium or long distance, the flash light emission will be stopped after the time Tb has elapsed. It is stopped when Tc elapses. As mentioned above, the light emitting time of the flash discharge tube 7 is controlled so that it becomes longer as the subject position is farther away, and as a result, as long as the subject is within a predetermined distance, it is uniformly illuminated regardless of the distance of the subject. Become. The flash discharge light emitting circuit described above is effective in providing appropriate illumination regardless of the distance to the subject, but it also has the following drawbacks. (1) It is well known that in photoelectric converters such as photo transistors and photo diodes, the generation of photoelectric conversion signals is delayed as the incident light becomes weaker. In direct photometry in which the light reflected from the film surface is received within the camera, the effect of the above-mentioned delay appears particularly because the light reflected from the film surface is weak. From this, the photoelectric conversion signal obtained by direct photometry is integrated using an integrating capacitor,
If the configuration is such that the flash discharge tube stops emitting light according to this integral value, the light control signal is generated after the point at which the flash light emission actually needs to be stopped, resulting in overexposed photography. I often end up. (2) The farther the subject is, the more the integration capacitor 14
Since the integration time becomes long, it is susceptible to the effects of other people's flash emissions. (3) When using the flash for backlit photography during the day,
Since the integral value of the integrating capacitor 14 is affected by brightness other than the reflected light from the object, illumination of the object may be insufficient. The present invention was developed in consideration of the above-mentioned circumstances, and its main purpose is to avoid the use of an integrating condenser, which has the drawbacks mentioned above, and to speed up the metering of the reflected light from the subject as much as possible to avoid the effects of ambient light. purpose. Therefore, the present invention provides a flash discharge light emitting device equipped with a light emission stop circuit that stops the flash light emission of the flash discharge tube in accordance with a light control signal from an automatic light control signal circuit. a photoelectric converter that receives the generated object reflected light and generates a photoelectric conversion signal in response to changes in the reflected light; and a first detection device that detects the start of light emission of the flash discharge tube and changes from the first state to the second state. The AND gate includes an AND gate that inputs a detection signal of a second detection circuit that changes from a second state to a first state upon detecting that the detection signal of the circuit and the photoelectric conversion signal reach a preset constant level; and a time measurement circuit that measures the time until the photoelectric conversion signal reaches a predetermined level from the gate output, and a voltage conversion that converts the measured time information into a linear function voltage based on the output of the time measurement circuit. circuit, a square calculation circuit that converts the above-mentioned linear function voltage to a quadratic function voltage, and a voltage conversion circuit that converts the above-mentioned quadratic function voltage to a linear function voltage, and changes the voltage conversion coefficient to adjust film sensitivity, aperture, etc. It includes a time expansion circuit configured to set an exposure factor, and a protection circuit that operates the time expansion circuit after the time measurement circuit measures the time, and the time expansion circuit uses the time expansion information as a dimming signal. An automatic dimming signal circuit for a flash discharge light emitting device is proposed. Next, embodiments of the present invention will be described with reference to the drawings. First, the basic principle of the present invention will be explained with reference to FIG. FIG. 3 roughly depicts a photoelectric conversion signal curve of a photoelectric converter that receives reflected light from an object, with the horizontal axis indicating time and the vertical axis indicating the magnitude of the photoelectric conversion signal. As can be seen from a comparison with Figure 2, the photoelectric conversion signal appears in the same way as the reflected light from the subject, so if the subject is located at a short distance, it will appear as curve 19, and if the subject is located at a medium or long distance, it will appear as shown in curve 19. curve 20,
It will be like 21. Now, in the present invention, a certain set level 22 is provided for the photoelectric conversion signals appearing like the curves 19, 20, and 21, and the photoelectric conversion signal is set at this level 22.
Measure the time until reaching 2. Note that the setting level 22 is determined in accordance with the peak value of the photoelectric conversion signal under the conditions of full light emission (flash light emission when light emission is not controlled) and proper exposure. The time measured in this way, for example, ta,
Since tb and tc correspond accurately to the subject distance, the effective time is smaller than these measurement times ta, tb, and tc.
An automatic dimming signal circuit can be constructed by determining Ta, Tb, and Tc and generating a dimming signal according to the effective time. The effective times Ta, Tb, and Tc are the times until the flash discharge tube actually stops emitting flash light. As a result of repeated research on the relationship between measurement time and effective time, the inventor of this application found that Ta=Kta ² , Tb=
It was found that there is a quadratic relationship between the measurement time and the effective time, such as Ktb ² and Tc = Ktc ² . The table shown below is data obtained through experiments.

[Table] In this experiment, the reflected light from the subject that enters the photoelectric converter is regulated by the aperture F, and the aperture F is set to 4, 5,
Change sequentially like 6, 8, 11, 16, measuring time
tn and effective time Tn are calculated. In addition,
In this experiment, the subject distance was set to 3 m and the film sensitivity condition was set to 100. FIG. 4 shows the relationship between the measurement time tn and the photoelectric conversion signal based on the above experimental results. As can be seen from the above experimental results, under the condition of aperture F = 4, the effective time Tn is approximately 3.5 times the measurement time tn, and in the case of F = 5.6, Tn is 5 times tn, and similarly, when F = 8 7 times when , 10 times when F = 11, F
= 16, it becomes 14 times. Therefore, if the measurement time tn is converted by the above-mentioned magnification, the effective time Tn for proper illumination light will be obtained, so that the formula Tn=0.25tn ² ...(1) should be satisfied. However, the above formula uses a subject distance of 3m and a film sensitivity of
100 conditions, so if you change these conditions, you need to change the coefficient 0.25 in the above equation. Therefore, in reality, the formula Tn=Ktn ² ...(2) is satisfied. In addition, in the above experiment, the subject distance was kept constant and the aperture F was sequentially changed, but the same result can be obtained even if the subject distance is changed to 4m, 5.6m, 8m, 11m, 16m under constant aperture conditions. is clear. From this, if we change K in the above equation (2) according to exposure factors such as film sensitivity or aperture, we get
Effective time Tn can be obtained according to the subject distance. Next, FIG. 5 is a block diagram showing an embodiment of the automatic dimming signal circuit according to the present invention. In this figure, comparators 23, 24 and AND gate 25 form a time measuring circuit. Comparator 23 is activated when the flash discharge tube starts emitting light.
A starting signal is input to the to terminal, and at the same time as this input, its output changes from low level to high level as shown in FIG. The comparator 24 inputs the photoelectric conversion voltage sent from the photoelectric converter and the reference voltage as a set level, and at the time tn when the photoelectric conversion voltage rises to the same value as the reference voltage, its output becomes as shown in FIG. Changes from high level to low level. Therefore, since a square wave pulse as shown in FIG. 3c appears as the output of the AND gate 25, the time until the photoelectric conversion voltage reaches the reference voltage is measured by the pulse widths to to tn. The block 26 is a constant current charging circuit, which charges the capacitor 27 with a constant current during the measurement time tn mentioned above. In other words, the measurement time tn is a linear function of charging pressure V
It forms a voltage conversion circuit that converts into Figure d
shows constant current charging characteristics. Block 28 is a square calculation circuit which stores a square calculation voltage αV ² of the converted voltage V in a capacitor 29. In addition, α
is a constant determined by the circuit configuration. Block 30 is a constant current discharge circuit, which discharges the squared voltage αV ² at a constant current and converts it into a linear function voltage, as shown in FIG. The comparator 31 detects the voltage when the square calculation voltage αV ² drops to a predetermined value, and changes its output from a low level to a high level as shown in FIG. The block 32 is a gate voltage generation circuit which operates upon receiving the output of the comparator 31 and applies a gate voltage to the SCR 33 included in the light emission stop circuit, and can be constituted by a well-known circuit such as a differentiating circuit. By configuring as described above, the measurement time tn output from the time measurement circuit is determined by the constant current charging circuit 2.
6. Time is expanded by a time expansion circuit consisting of a square calculation circuit 28, a constant current discharge circuit 30, and a comparator 31. As a result, when the effective time Tn elapses after the flash discharge tube starts emitting light, a dimming signal is generated as an output of the comparator 31, and this dimming signal is supplied to the light emission stopping circuit. Furthermore, since the value of the coefficient K in equation (2) above is determined by the charging characteristics of the constant current charging circuit 26 and the discharging characteristics of the constant current discharging circuit 30, exposure factors such as film sensitivity and aperture are determined by the charging characteristics described above. It can be easily set by changing the characteristics or discharge characteristics. FIG. 6 shows a specific circuit example of the above-mentioned automatic dimming signal circuit. In this figure, the upper circuit is a known flash discharge emitter circuit, and the lower circuit is an automatic dimming signal circuit. The flash discharge emitter circuit is connected to the trigger switch 34.
The SCR of the trigger circuit by closing the
Since 35 is conductive, trigger capacitor 3
The trigger transformer 37 applies an excitation voltage to the flash discharge tube 38 due to the discharge of the capacitor 39, and the voltage of the gate resistor 40 appearing due to the discharge of the capacitor 39 is applied to the gate of the SCR 41. Than this,
When the SCR 41 becomes conductive, the flash discharge tube 38 receives electrical energy from the main discharge capacitor 42 and starts emitting flash light. On the other hand, since the charge in the capacitor 39 is discharged through the Zener diode 43, the voltage appearing across the diode 43 is supplied to the automatic dimming signal circuit as a light emission starting signal. Note that the commutating capacitor 44 and SCR 45 connected in a loop to the SCR 41 are the same light emission stop circuit as the conventional example shown in FIG.
The output voltage of the DC-DC converter is applied to . In the automatic dimming signal circuit shown in the lower row, a low voltage, for example, 6V, is applied to the terminals 48 and 49 almost at the same time as the power switch of the flash discharge light emitter circuit is turned on. Therefore, the light emission start signal is transmitted to the comparator 50.
At the same time as the signal is input, the output of the comparator 50 changes from low level to high level. Further, the light reflected from the object based on the flash light emission of the flash discharge tube 38 is photoelectrically converted by the photoelectric converter 51, and this photoelectric conversion voltage is inputted to one input terminal of the comparator 53 via the amplifier 52. The other input terminal of the comparator 53 has resistors 54 and 5.
Since the reference voltage adjusted by 5 is applied, when the photoelectric conversion voltage reaches the reference voltage, the output of the comparator 53 changes from high level to low level. Therefore, the output of the next-stage comparator 56 similarly changes from high level to low level. As can be seen from the above, comparators 50, 56
forms a kind of AND gate, and while the output of this AND gate maintains a high level,
That is, until the photoelectric conversion voltage reaches the reference voltage, the constant current charging circuit including the operational amplifier 57 charges the capacitor 58, and the operational amplifier 5
A square calculation circuit including 9 calculates the square of the charging voltage V of the capacitor 58. However, because the above square calculation circuit has an output of αV ² + αV due to its circuit configuration,
A subtraction circuit including an operational amplifier 60 subtracts the charging voltage αV so that only the voltage αV ² is charged to the capacitor 61. Note that a diode 62 provided between the subtraction circuit and the capacitor 61 is for preventing backflow. Square calculation voltage αV ² charged in the capacitor 61
is discharged by a constant current discharge circuit including an operational amplifier 63, but a protection circuit for the transistor 64 is provided so that this discharge is started from the time the time measurement is completed. That is, when the output of the comparator 53 is at a high level, the transistor 64 is turned on and short-circuits the input voltage resistors 65 and 66, so there is no output from the operational amplifier 63 and the transistor 67 remains off. When the output of the comparator 53 changes from high level to low level, the transistor 64 turns OFF.
The transistor 67 is turned on by the output of the operational amplifier 63, and constant current discharge is performed. Square calculation voltage αV ² stored in capacitor 61
falls due to the above-mentioned constant current discharge, and when this voltage αV ² drops to a predetermined voltage value, the output of the comparator 68 changes from low level to high level, and the high level output of this comparator 68 is used for dimming. The signal is input to the gate voltage generation circuit 69 as a signal. The gate voltage generation circuit 69 operates in response to the input of the dimming signal and generates a gate voltage for the SCR 45, so that the SCR 45 becomes conductive and the light emission stop circuit controls light emission. In the specific circuit example described above, exposure factors such as film sensitivity and aperture can be set by the variable resistor 70 of the constant current charging circuit or the variable resistor 71 of the constant current discharging circuit. Furthermore, since the comparator 68 is configured such that the square calculation voltage αV ² is applied to one input terminal and the reference voltage is applied to the other input terminal, the square calculation voltage αV ² is so low as to be less than the reference voltage. Even in such a case, the comparator 68 operates reliably and generates a dimming signal. Therefore, the dimming operation of the flash discharge light emitting device is compensated even in flash photography at a very close distance. In addition, in the embodiment shown in FIG. 5 described above, the converted voltage V
Both of the circuits for calculating the square calculation voltage αV ² are configured as a charging circuit, and the constant current discharging circuit 30 is configured as a discharging circuit. As mentioned above, the charge/discharge characteristic diagrams when carried out in this manner appear as shown in FIGS. 7a and 7b. However, in implementing the present invention, the circuits for determining the converted voltage V and the square calculation voltage αV ² can both have a discharge circuit configuration, as shown in the charge-discharge characteristic diagrams in FIGS. 7c and d. . In this case, a constant current charging circuit may be provided in place of the constant current discharging circuit 30. Further, the circuit for determining the converted voltage V can be configured as a charging circuit, and the circuit for determining the square calculation voltage αV ² can be configured as a discharging circuit. In this case, a constant current charging circuit is provided in place of the constant current discharging circuit 30. When carried out in this way, the charge/discharge characteristic diagram becomes
It appears as shown in Figures a and d. Furthermore, the circuit for determining the converted voltage V may be configured as a discharging circuit, and the circuit for determining the square calculation voltage αV ² may be configured as a charging circuit. In this case, the square calculation voltage αV ² is discharged by the constant current discharge circuit 30. When carried out in this manner, charge-discharge characteristic diagrams appear as shown in FIGS. 7b and 7c. As mentioned above, since the automatic dimming signal circuit according to the present invention does not include a photometric integration capacitor, it does not have the drawbacks caused by an integration capacitor, and also takes a long time until the photoelectric conversion signal reaches the set level. Since it is configured to measure and generate a dimming signal,
Even when the reflected light from the object that enters the photoelectric converter is weak, the amount of light emitted can be accurately controlled. Furthermore, since the photometry time is extremely fast, malfunctions caused by ambient light such as flashlights from other people are extremely rare.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram of a flash discharge emitter showing a conventional example.
Fig. 2 is an explanatory diagram showing the luminescence time of the flash discharge tube according to the subject distance, Fig. 3 is an explanatory diagram showing the relationship between measurement time and effective time, and Fig. 4 is an explanatory diagram showing the relationship between the photoelectric conversion signal and measurement time. FIG. 5 is a block diagram showing an embodiment of the automatic dimming signal circuit according to the present invention, and FIG. 6 shows a specific circuit example of the automatic dimming signal circuit described above. In the circuit diagram, FIGS. 7a and 7b are charging and discharging characteristic diagrams of the embodiment in FIG. 5, and FIGS. 7c and d are charging and discharging characteristic diagrams when a part of the circuit of the embodiment in FIG. 5 is replaced. 23, 24, 50, 53, 56... Comparator, 26, 57... Constant current charging circuit, 28, 5
9, 60... Square calculation circuit, 30, 63... Constant current discharge circuit, 32, 69... Gate voltage generation circuit, 64... Transistor for protection circuit.

Claims (1)

[Scope of utility model registration request] In a flash discharge light emitting device equipped with a light emission stop circuit that stops the flash light emission of the flash discharge tube according to a dimming signal from an automatic light control signal circuit, the light reflected from the object caused by the flash light emission of the flash discharge tube is Receives light,
a photoelectric converter that generates a photoelectric conversion signal in response to a change in reflected light; a detection signal of a first detection circuit that detects the start of light emission of a flash discharge tube and changes from a first state to a second state; and the photoelectric conversion signal. includes an AND gate that inputs a detection signal of a second detection circuit that changes from a second state to a first state upon detecting that the signal has reached a predetermined level; a voltage conversion circuit that converts the measured time information into a linear function voltage based on the output of the time measurement circuit; and a voltage conversion circuit that converts the measured time information into a linear function voltage; It includes a square calculation circuit that converts to a quadratic function voltage, and a voltage conversion circuit that converts the quadratic function voltage to a linear function voltage, and changes the voltage conversion coefficient to set exposure factors such as film sensitivity and aperture. It is characterized by comprising an expansion circuit and a protection circuit that operates the time expansion circuit after the time measuring circuit measures the time, and the time expansion circuit outputs time expansion information as a dimming signal. Automatic dimming signal circuit for flash discharge light emitters.