JPH01172821A - Flash light emission device with automatic dimming function - Google Patents

Abstract

PURPOSE:To reduce the excessive light emission of flash light by varying a reference signal to be compared with the integral signal of subject reflected light with flash light emission time, and advancing a light emission stopping operation time point according to the distance to a subject. CONSTITUTION:In short-distance photography, the point of time when an integral signal curve C and the reference signal A meets each other is T2 and a light emission stop signal is outputted at this point of time, but a conventional reference signal B meets the integral signal curve C at a point T3 in short-distance photography and the light emission stop signal is outputted at this point of time. Namely, the generation of the light emission stop signal is advanced by a period T2-T3. In long-distance photography, on the other hand, the generation of the light emission stop signal is advanced by a period T4-T5, which is shorter than the period T2-T3 in the short-distance photography. Thus, the light emission stop operation point T2 is advanced as compared with a conventional point T3 and a flash light emission curve E is obtained. Consequently, the excessive light emission quantity is reduced as compared with a conventional flash light emission curve F.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a flash light emitting device having a function of automatically determining the amount of light emitted according to the distance to a subject, that is, a so-called automatic light control function.

"Prior Art" Flash light emitting devices with an automatic light control function have been widely known, and various configurations have been proposed.

FIG. 5 is a circuit diagram of a typical conventional example.

In this circuit, 11 is a battery power supply, 12 is a power switch, 1
3 is a converter, 14 is a rectifying diode, and these members 11 to 14 form a power supply circuit consisting of a DC-DC converter.

A main discharge capacitor 15 stores electrical energy, and the main discharge capacitor 15 is charged to a predetermined voltage by driving the power supply circuit.

16 is a flash discharge tube that discharges the energy stored in the main discharge capacitor 15 and converts it into light energy.

17 is a trigger capacitor, 18 is a trigger transformer,
19 is 5CR12 as a trigger switching element
0 is a starting signal terminal, 21 is an excitation electrode, and these members 17 to 21 form a trigger circuit that applies an excitation voltage to the flash discharge tube 16 to start emitting light.

That is, when a starting signal is applied to the starting signal terminal 20 from the camera side, 5CR19 is transferred to a conductive state, and the charge of the trigger capacitor 17 is transferred to the trigger transformer 1.
8, the high voltage pulse induced in the secondary coil is applied to the excitation electrode 21.

As a result, the flash discharge tube 16, which has become low in impedance, discharges the charge in the main discharge capacitor 15 and starts emitting flash light.

22 is a commutating capacitor, and a series circuit of a resistor 23.24° and a capacitor 25 forms an impedance circuit.
When the flash discharge tube 16 starts discharging, its initial current flows through the commutating capacitor 22 to the impedance circuit, and the 5CR 26 receives the voltage change of the impedance circuit at its gate and becomes conductive.

27 is an SCR as a switching element, and this 5CR
27 and the commutating capacitor 22 form a light emission stop circuit.

The commutating capacitor 22 is charged in advance to the polarity shown in the figure via the resistors 28 and 29, and this charging voltage is applied as a reverse voltage between the anode and cathode of the 5CR26 due to conduction of the 5CR27, and the capacitor 2 of the impedance circuit is
5 is discharged through the 5CR 27 and a reverse gate voltage is applied, so the 5CR 26 becomes non-conductive and the flash discharge tube 16 stops emitting flash light.

On the other hand, 30 is a comparator, 31 is a variable resistor for generating a reference signal, 32 is an integrating capacitor, 33 is a phototransistor, 34, 35, 36 is a transistor, and 37 is a starting signal terminal, which forms a photoresponse circuit. ing.

A starting signal is input to the terminal 37 of this circuit together with the trigger starting signal terminal 20 described above, the transistor 36 is turned on, the subsequent transistor 34 is turned on, and the transistor 35 is turned off.

From this, the phototransistor 33 enters the power supply state,
The photoelectric conversion current flows into the integrating capacitor and is integrated.

When the integral value of the integrating capacitor 32 reaches a predetermined value, the output of the comparator 30 becomes a high voltage, turning on the transistor 38.

As a result, transistor 39 temporarily becomes ONL, 5CR
27 becomes conductive upon receiving the gate voltage, the flash light emission is stopped by the operation of the above-mentioned light emission stop circuit.

Note that 40 is a current limiting coil, and 41 is a diode for absorbing back electromotive force.

"The problem that the invention attempts to solve" The above flash light emitting device has the following problems.

Even though a light emission control circuit including a light response circuit and a light emission stop circuit performs a light emission stop operation, flash light emission continues for a short time from the time of this stop operation, and then the light emission stops.

The reason is that the 5CR2 connected in series to the flash discharge tube 16
6 becomes non-conductive, the discharge current of the flash discharge 'ff16 continues to flow through the path of the commutating capacitor 22.5CR27, charging the commutating capacitor 22 so that it has a polarity opposite to that shown in the figure. It is. The flash light emission caused by such an operation continues until the commutating capacitor 22 reaches a predetermined charging voltage, and this becomes surplus light emission.

Note that since the resistor 28 has a high resistance that allows a current to flow below the conduction maintenance current of 5CR27, the discharge current flowing through the commutating capacitor 22 is reduced, so that the 5CR2
7 becomes non-conductive.

Figure 6 shows the state of flash emission during close-up photography.
The figures show the states of flash emission during long-distance photography.In the case of close-range photography, there is sufficient charging energy in the main discharge capacitor 15, so excess light is emitted as shown by the diagonal lines in Figure 6. It shows up in a big way.

Therefore, the ratio of the surplus light emission amount to the total flash light emission amount is large, resulting in an excess light amount.

Further, in the case of long-distance photography, the charging energy of the main discharge capacitor l5 is considerably discharged.

As shown by diagonal lines in FIG. 7, there is little surplus light emission and its proportion to the total amount of flash light emission is small, so its influence is small.

"Means for Solving the Problems" The present invention has been developed in view of the above-mentioned problems, and includes an integrator that refines the light reflected from the subject by the flash emission of the flash discharge tube as an electrical signal, In a flash light emitting device equipped with a light emission control circuit that stops the flash operation of the flash discharge tube in response to The present invention is characterized by comprising a comparator that outputs a comparison signal as a light emission stop signal, and a light emission amount correction circuit that changes the reference signal of the comparator as the flash emission time elapses to hasten the generation of the light emission stop signal. We propose a flash light emitting device.

``Function'' The reference signal of the comparator is changed by the light emission amount correction circuit as the flash firing time elapses, and the time point at which the light emission stop signal is generated is determined by comparing the integral signal from the reflected light from the subject with the reference signal. The speed increases depending on the distance, and excessive flash light emission is minimized.

"Example" Next, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram of a flash light emitting device according to the present invention, and the same circuit components as those of the conventional circuit shown in FIG. 5 will be described with the same reference numerals.

Further, FIG. 2 is a time chart showing signal levels in each part of the circuit.

In this circuit, blocks 42, 43, and 44 are all one-shot multivibrators (hereinafter simply referred to as multi), block 45 is a delay circuit, and block 46 is a regulator.

The multi 42 forms a starting circuit that inputs a negative pulse signal S1 from the camera side, and is inverted when the signal S falls and outputs a high level signal S2. The output signal S2 is set by the multifunction device 42 so that it continues for a period of time slightly longer than the full light emission time of the flash discharge tube 16, that is, the time required for the flash light emission to end without being controlled.

The high output signal S2 of the multi-channel 42 turns the transistor 48 ON, and then the transistor 49 in the subsequent stage is turned ON temporarily.

As a result, the positive pulse signal S sent as the output of the transistor 49 is sent to the gate of the 5CR 19, and the flash discharge tube 16 starts emitting flash light by the operation of the trigger circuit.

On the other hand, the multi 43 to which the signal S2 is input is inverted by the rise of the signal S2 and outputs a low level signal S4.

This signal S4 is Lo during the full light emission time of the flash discharge tube 16.
The transistor 34 is set to continue at the w level.
．． Send it to the base of 35.

Therefore, the transistor 34 is turned on, the transistor 35 is 0FFL, and the phototransistor 33 is in a power supply state through the regulator 46. From this point on,
The photoelectric conversion current of the phototransistor 33, which receives the light reflected from the object due to flash emission, flows into the integrating capacitor and starts integration.

The integral signal S7 integrated by the integrating capacitor 32 is input to one input terminal of the comparator 30.

Further, the delay circuit 45 to which the signal S2 is input outputs a signal Ss obtained by delaying the signal S2 by a certain period of time and sends it to the multiplexer 44.

The multiplexer 44 inputs the signal S, outputs a high level signal S6 during the full light emission time, and sends this signal SG to the capacitor 50 via the resistor 52.

The capacitor 50 is configured to be charged by the divided voltage of the resistor 31.51, and the signal SG is applied so as to be superimposed on the charging voltage of the capacitor 50.

The voltage applied to the capacitor 50 from the regulator 46 via the resistor 51 is a constant voltage, but since the capacitor 5o is transiently charged by the signal SG,
A reference signal S that combines both.

is applied to the other input terminal of the comparator 3o.

This reference signal S shows a constant value at the initial stage of flash emission, then increases according to the CR time constant, and draws a curve that saturates after a certain period of time.

The integral signal S7 and the reference signal S are compared, and the integral signal S7 is
When the signal reaches the predetermined reference signal S, the comparator 3
0 is inverted and a High level signal S is output.

As a result, the transistor 38 is turned on, the subsequent transistor 39 is temporarily turned on, and the positive pulse signal S
1° is sent to the gate of 5CR27, and the flash emission of the flash discharge tube 16 is stopped as described above.

As mentioned above, in this embodiment, the reference signal S to be compared with the integral signal S7 is increased as time passes.
The inversion point of the comparator 30 is advanced in accordance with the distance to the reflected light from the object, and a light emission stop signal is output.

That is, it becomes as shown in FIG.

In this figure, the reference signal A of this embodiment is the flash emission time T. to T becomes constant due to the action of the delay circuit 45, and thereafter a charging curve is drawn due to the CR time constant, but the conventional reference signal B becomes a level signal.

In close-range photography, the time point at which the integral signal curve C and the reference signal A of this embodiment match is T2, and a light emission stop signal is output at this point. The time point at which it coincides with the integral signal curve C is T, and
At this point, a light emission stop signal is output.

In other words, in the case of close-up shooting, the generation of the 1 flash stop signal is T2.
It will be accelerated by ~T3.

On the other hand, in long-distance photography, the light emission stop signal is output at time T4 when the integral signal curve matches the reference signal A of this embodiment, but when the conventional reference signal B is used, in long-distance photography The time point at which the integral signal plane gD coincides with T,
At this point, a light emission stop signal is output.

As a result, the time to accelerate the generation of the flash stop signal for long-distance shooting is between 14 and 15, while for close-range shooting the time is T2 to 15.
It will be shorter than the time T1.

As described above, since the light emission stop signal is output earlier than before, as shown in FIG. Compared to the conventional flash light emission curve F, the amount of surplus light emission is extremely small.

Note that the reference signal of this embodiment is based on the delay time of the multi-layer 44 and the resistors 31, 51, 52, . By appropriately selecting the constant of the capacitor 50, it is possible to reduce the amount of excess light emitted, and a function signal generator or the like may be used to generate the reference signal.

"Effects of the Invention" As described above, the flash light emitting device according to the present invention has the following features:
The reference signal to be compared with the integrated signal of the light reflected from the object is changed as the flash emission time elapses, and the flash stop operation time is brought forward according to the distance from the object.

That is, in close-range photography, the time point at which the light emission stop signal is generated is the earliest at the beginning of flash emission, and as the flash emission progresses, the time point at which the light emission stop signal is generated becomes progressively fewer.

Therefore, the flash light emitting device has extremely little overexposure due to redundant flash emission in close-range photography, and provides proper exposure even in intermediate to long-distance photography.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a flash light emitting device showing an embodiment of the present invention, FIG. 2 is a time chart showing signal states of each part of the circuit, and FIG. 3 is a light emitting diagram of the above flash light emitting device and a conventional example. An explanatory diagram showing the difference in the point of stop operation, Fig. 4 is a diagram showing a flash emission curve in close-range photography using the above flash emitting device, Fig. 5 is a circuit diagram of a conventional flash emitting device, and Fig. 6 71 is a diagram showing a flash light emission curve for close-up photography using the flash light emitting device of FIG. 5, and FIG. 71 is a diagram showing a flash light emission curve for long distance photography using the flash light emitting device of FIG. 13... Converter 15... Main discharge capacitor 16... Flash discharge tube 22... Commutation capacitor 30... Comparator 32... Integrating capacitor 33... Phototransistor 42.43.44...One-shot multivibrator 45...Delay circuit 46...Regulator 2nd Figure 54-■-11--11--]-5/9 3rd Figure 4 □ Time Figure 6 Figure 7 x 吋91

Claims (1)

[Claims] The above-mentioned flash light emitting device includes an integrator that integrates light reflected from a subject due to flash emission of a flash discharge tube as an electric signal, and includes a light emission control circuit that stops the flash operation of the flash discharge tube according to a predetermined integral value. A comparator that compares the integral signal of the integrator with a reference signal and outputs a comparison signal as a light emission stop signal when these signal values reach a predetermined relationship, and a comparator that outputs a comparison signal as a light emission stop signal. 1. A flash light emitting device, comprising: a light emission amount correction circuit for accelerating the generation of the light emission stop signal.