JPH054651B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic light control device that changes the ratio of natural light to strobe light in accordance with subject brightness during daytime synchronized photography.

If the main subject is dark compared to the background, such as in backlighting, the main subject will be underexposed, but daytime synchronized shooting (AE shooting with a strobe)
If you do this, the main subject will be illuminated with strobe light, so it is possible to properly expose this main subject as well.
Many compact cameras and instant cameras with built-in strobes are designed to perform daytime synchronization.

Recently, as described in Japanese Unexamined Patent Publication No. 56-149022, a device has been proposed in which a strobe light is constantly emitted. This device uses a flash mechanism consisting of a photointerrupter that moves in conjunction with the distance adjustment knob on the lens, and a sensor plate that is located between the photointerrupters and moves in conjunction with a programmable shutter blade. It is provided. The amount of light emitted by the strobe is determined in advance before the shutter is opened according to the brightness of the subject, and the strobe emits light when the aperture reaches the aperture set by the flash mechanical mechanism. Below the subject brightness at which the proportion of natural light contributing to film exposure becomes zero, the amount of light emitted by the strobe is maintained at its maximum value. Between this subject brightness and the subject brightness at which the shutter speed reaches the camera shake limit, the amount of light emitted by the strobe changes so that the strobe light and natural light are inversely proportional. When the subject brightness exceeds the camera shake limit shutter speed, the amount of strobe light is kept at a minimum value, and exposure is performed at a ratio of 75% natural light and 35% strobe light.

However, in the above-mentioned apparatus, during daytime synchronized photography, if the subject brightness is high and the subject is far away, the shutter starts closing before reaching the aperture aperture determined according to the distance. In this case, as with conventional synchro devices, the strobe fires when the shutter starts to close, but since the aperture aperture is smaller than the planned value, it is difficult to expose the film. The proportion of contributing strobe light decreases, making it impossible to perform accurate proportional control according to the subject brightness.

Furthermore, when photographing indoors or photographing in the morning or evening when the subject brightness is low, the color temperature of the scene light changes, resulting in poor color reproducibility, and improvements in this respect are also desired.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned drawbacks, and it is an object of the present invention to provide an automatic light control device that can reduce the influence of changes in the color temperature of scene light.

Another object of the present invention is to prevent the ratio of strobe light and natural light from changing depending on the subject brightness and shooting distance even when the subject brightness is the same, and to always perform desired proportional control. It is an object of the present invention to provide an automatic light control device as described above.

The present invention is designed to increase the proportion of strobe light as the subject brightness decreases during daytime synchronized photography.

Embodiments of the present invention will be described in detail below with reference to the drawings.

In FIG. 1, a booster circuit 1 includes an oscillator and a booster transformer, as is well known, and is connected to a power source via a power switch. The alternating current boosted by this booster circuit 1 is rectified by a diode 2 and then supplied to a main capacitor 3.

The trigger circuit 4 is composed of a trigger capacitor and a step-up transformer, and when the thallister 5 turns on, the trigger capacitor is discharged to generate a high voltage, and this high voltage is applied to the trigger electrode 6a of the flash discharge tube 6. Apply. At the same time, a gate signal is supplied to the gate of the light emitting thyristor 7 to turn it on.

The light emission of the flash discharge tube 6 is stopped when the cut-off thyristor 8 is turned on. That is, the commutation capacitor 11 is charged with the current flowing through the resistors 9 and 10, and when the cut-off thyristor 8 is turned on, the commutation capacitor 11 discharges and reverse biases the light-emitting thyristor 7. By turning off, the flash discharge tube 6 stops emitting light.

When the subject brightness is below the camera shake limit shutter speed, e.g. 1/32 second, the trigger circuit 4 detects the point at which the shutter blade changes from opening to closing (also at the point when the shutter reaches full open), as is well known. (including), and when the subject brightness is higher than or equal to the subject brightness, the trigger is activated when the aperture reaches a predetermined relatively small aperture.

The subject brightness at which the shutter speed reaches the camera shake limit varies depending on the shutter program diagram, but in the case of the program diagram shown in Figure 3, it is LV8.
(ASA100). At LV8 or above, in order to widen the range in which the ratio of natural light and strobe light that contributes to film exposure can be maintained at the desired value, the aperture is set as small as possible, taking into account the amount of light emitted by the flash discharge tube 6. Range: For example, aperture is F5.61/3 to F8
Within this range, the trigger is activated when the aperture, which is determined by proportionately distributing the brightness of the subject, is reached.

In order to detect that the aperture for applying this trigger has been reached, a light receiving element 12 that measures the subject brightness;
A series circuit including a capacitor 13 and a resistor 14 is provided. Switch 1 is connected in parallel with this capacitor 13.
5 is connected and turns off when the shutter starts to open. The terminal voltage of the capacitor 13 is connected to one side input terminal of a comparator 16, and the + side input terminal of this comparator 16 is connected to the connection point between the resistors 17 and 18.
The capacitor 13 is charged with a current according to the subject brightness, and when the terminal voltage reaches a predetermined voltage, the output terminal of the comparator 16 becomes "L". The timing at which the output terminal of the comparator 16 is inverted to "L" is LV8 as shown in FIG.
This is when the aperture reaches F5.61/3, and as the LV increases, the value changes proportionally, and the value changes proportionally to LV14.5.
Here, the aperture is F8. This comparator 16
When the voltage becomes "L", the transistor 19 turns on, and its collector voltage becomes a high voltage (H). At LV8 or higher, the output of the AND circuit 20 becomes "H", so this is used as a gate signal to connect the diode 2.
1 to the gate of thyristor 5, which can be turned on.

At LV8 or higher, in addition to the gate signal generated from the AND circuit 20 during the shutter opening operation as described above, when the synchro switch 22 is turned on when the shutter starts closing operation or when the shutter is fully opened, the AND circuit generates a gate signal. A gate signal will be generated from 24. In order to prevent this, a flip-flop 23 is provided.
When the output terminal of the AND circuit 20 becomes "H", the flip-flop 23 is set, and the output signal from its output terminal Q is inputted to one input terminal of the AND circuit 24.

On the other hand, when the subject brightness is below LV8 (when using ASA100) or when the subject brightness causes the shutter to close before the aperture reaches F8 (LV14.5 or above in the case of the shutter shown in Fig. 3), the AND circuit 20 The output remains at "L". In this state, the flip-flop 23 is not set, so the output terminal is at "H". and,
The synchro switch 22 is turned on when the shutter blade changes from opening to closing.
The output terminal of the AND circuit 24 becomes "H", and a gate signal is sent to the thyristor 5 through the diode 25 to turn it on.
Incidentally, the flip-flop 23 may be reset when the shutter is closed.

A light receiving element 31 and a variable resistor 32 are connected in series to detect the brightness level of the subject. The connection point between the light receiving element 31 and the variable resistor 32 is connected to the + side input terminal of the comparator 33, and the sliding terminal of the variable resistor 34 is connected to the comparator 33.
One side input terminal of is connected. The output terminal of this comparator 33 becomes "H" when the voltage is LV8 or higher, and becomes "L" when the voltage is lower than LV8.

The diodes 35 and 36 constitute an OR circuit, and the anodes are connected to the sliding terminals of the variable resistor 32 and the variable resistor 37, respectively.
At LV5 to LV6, the cathode voltage of diode 36 is higher, and at LV6, the cathode voltages of diodes 35 and 36 are equal. From beyond LV6 to LV8, the cathode voltage of diode 35 is higher,
Its value increases depending on the LV value.

The output of the OR circuit of the diodes 35 and 36 is input to the base of the transistor 38, and the collector current flows in accordance with the base current.
This appears as a change in collector voltage. This collector voltage and the voltage at the sliding terminal of the variable resistor 39 are:
It is sent to the analog switch circuit 40 and selected by the output of the comparator 33. That is,
When LV8 or higher, the voltage taken out from the variable resistor 39 is inputted to one side input terminal of the comparator 41 as the dimming level, and when it is below LV8, the collector voltage of the transistor 38 is used as the dimming level.

Reflected light from the subject illuminated by the strobe light enters the phototransistor 42. When the switch 43 is turned off at the same time as the strobe light is irradiated, the capacitor 44 is charged by the photocurrent of the phototransistor 42. When the terminal voltage of this capacitor 44 slightly exceeds the voltage corresponding to the dimming level input to the negative input terminal, the output terminal of the comparator 41 becomes "H", turning on the interrupting thyristor 8 and discharging a flash. Light emission from tube 6 is stopped.
The variable resistors 34, 39 and 45 are adjusted according to the film sensitivity.

FIG. 2 shows an example of an automatic exposure control device for a program shutter that can be used with the apparatus of the present invention. The shutter control circuit 50 is connected to a power source 52 via a power switch 51. A light-receiving element 53 and a transistor 54 that photoelectrically convert the light from the subject are connected in series.
Since the output terminal of the OR circuit 55 becomes "H" when the voltage is below LV8 (for ASA100), the transistor 54 is turned off, and at other times, the transistor 5 is turned off.
4 turns on. When the transistor 54 is in the on state, when the release button is pressed, the switch 56 is turned off at the same time as the shutter starts to open, and the capacitor 57 is charged with the photocurrent flowing through the light receiving element 53. When the capacitor 57 reaches a predetermined voltage, the current flowing through the magnet 58 is cut off and the shutter begins to close as is well known.

The series circuit of the resistor 59 and the transistor 60 is
This is to fix the shutter speed to, for example, 1/32 second, which is above the camera shake limit speed and opens the aperture when the strobe is in use and the subject brightness is below LV8. For this purpose, OR circuit 55
After the output signal of is inverted by the inverter 61,
It is input to the base of the transistor 60.

The variable resistor 62 is adjusted according to the film sensitivity, and a resistor 6 is connected in series with this variable resistor 62.
3,64 are connected. A transistor 65 is connected in parallel to the resistor 64, and is turned off when the strobe is used. The signal indicating the use status of the strobe can be obtained from, for example, a main switch of the strobe or a switch that is turned on in conjunction with the pop-up of a movable strobe. When the strobe is not used, the transistor 65 is on, so the voltage at the connection point 66 is low. On the other hand, when a strobe is used, the voltage at the connection point 66 becomes high because the transistor 65 is turned off. Therefore, in automatic exposure without using a strobe, the film exposure amount will be the appropriate value, but when using a strobe, for example, even if you use ASA100 film, the automatic exposure will be the same as when using ASA125 film. The film exposure amount will be approximately 80% of the appropriate value. In this way, daytime synchronization reduces the amount of natural light and uses strobe light to at least make up for this deficiency. Of course, the ratio of this natural light and strobe light is based on the flash discharge tube 6
It is determined to a desired value by taking into account the amount of light emitted from
You can also overexpose by 1/3 aperture at 25%.

FIG. 5 shows a shutter program diagram. Open aperture (F2.8) when light value (LV) is below 10.
Therefore, only the shutter speed changes. At LV10 and above, both aperture and shutter speed change. Note that when using a strobe and the brightness is low, such as LV8 or lower, the limiter operates as described above, and the shutter speed is fixed at, for example, 1/32 second.

FIG. 4 shows the dimming level, and changes in the amount of light are expressed with an aperture scale. The aperture scale (F value) indicates the proportion of the strobe light that contributes to film exposure when the strobe light is emitted at that aperture at a distance where strobe photography is possible.
It becomes 100%, indicating that proper exposure can be obtained. A signal corresponding to the dimming level is input to the negative input terminal of the comparator 41 shown in FIG.

For LV8 to 16, the light output level is set to the maximum, and the timing of the flash is determined by the aperture.
This is the point when the aperture is in the range of F5.61/3 to F8 and proportionally distributed at LV8 to 16. At LV6, where natural light does not contribute to film exposure, the shutter moves fully open (F2.8) and starts firing when it closes, so the light control level is set to a medium amount of light. Between LV6 and LV8, natural light also contributes to film exposure, so in order to smoothly increase the proportion of strobe light, the light control level is set to be inversely proportional to natural light. This inversely proportional relationship between natural light and strobe light may be changed linearly as in this embodiment, or may be changed curved or stepwise.

FIG. 5 shows the ratio of natural light and strobe light. If the light emission of the flash discharge tube 6 is controlled under the dimming level and light emission timing shown in Fig. 4, natural light will be approximately 80% of the appropriate exposure value and strobe light will be at the appropriate exposure value at LV8 and above, which is synchronized during the day. It varies depending on the LV value in the range of about 40% to about 25% of the value. In low-luminance photography, which is the case for most indoor photography and photography in the morning and evening, the proportion of strobe light with a color temperature close to that of sunlight is high at about 40%, resulting in images with colors that are true to the subject.

Under LV6, the strobe light is 100% of the appropriate exposure amount.
This is the same as normal flash photography.

Between LV6 and 8, the strobe light will decrease from 100% to approx.
40%, and natural light changes from 0% to about 80%.

Note that at LV6 or higher, the film exposure amount exceeds 100%, so the excess amount is overexposure, but it is preferable to have a slight overexposure because the print quality will be better. Also, when shooting without using a strobe, exposure is performed at an appropriate value that captures 100% natural light.

Next, the operation of the above embodiment will be explained. During strobe photography, the transistor 65 shown in FIG. 2 is turned on, so the energization time of the magnet 58 is controlled so that exposure is performed at approximately 80% of the appropriate exposure amount. The main capacitor 3 is charged to a predetermined voltage by the booster circuit 1 shown in FIG. 1, and the flash discharge tube 6 is prepared to emit light.

When the subject brightness is LV5-6 (ASA100), the cathode voltage of the diode 36 is the same as that of the transistor 38.
A constant voltage is generated at its collector. Since the output terminal of the comparator 33 is "L" at the time of LV5 to LV6, the collector voltage of the transistor 38 is inputted to the negative input terminal of the comparator 41 as a dimming level. In this case, if the shooting distance is the same, a medium amount of light is output from the flash discharge tube 6, as shown in FIG.

At LV6 to 8, the resistance value of the light receiving element 31 becomes small, so that the cathode voltage of the diode 35 becomes larger than that of the diode 36 (the same at LV6). Since this cathode voltage changes depending on the brightness of the subject, the transistor 38
The collector voltage of the subject decreases depending on the brightness of the subject. Therefore, the flash discharge tube 6 outputs an amount of light that is inversely proportional to the subject brightness.

For LV8 to LV16, the output of the comparator 33 is "H", so the constant voltage taken out from the variable resistor 39 is output to the comparator 41 as the dimming level.
is input to the - side input terminal of.

When the release button is pressed, a switch 56 shown in FIG. 2 is turned off, and a capacitor 57 is charged with a photocurrent flowing through the light receiving element 53. Since the magnet 58 is energized while the capacitor 57 is being charged, the shutter blades move away from each other and the shutter starts to open.

When LV8 or lower, the resistor 59 shown in FIG. 2 acts as a limiter, and the aperture is fixed at F2.8 and the shutter speed is fixed to 1/32 seconds, for example, at which no camera shake occurs. When the shutter blade reaches its full opening and starts its closing operation, the synchro switch 22 is turned on.
The output terminal of the AND circuit 24 becomes "H", and the thyristor 5 is turned on. The trigger circuit 4 starts operating and turns on the light emitting thyristor 7, and at the same time applies a high voltage to the trigger electrode 6a of the flash discharge tube 6 to cause the flash discharge tube 6 to emit light.

At the same time as the flash discharge tube 6 emits light, the switch 43
is turned off, the photocurrent of the phototransistor 42, which measures the reflected light from the subject, connects the capacitor 44.
is charged. When this capacitor 44 is charged to the above-mentioned dimming level, the output of the comparator 41 becomes "H" and the cutoff thyristor 8 is turned on. When the cut-off thyristor 8 is turned on, the light-emitting thyristor 7 is reverse biased by the discharge current of the commutation capacitor 11 and turned off, and the flash discharge tube 6 stops emitting light.

When the voltage is LV8 or higher, the switch 15 is opened when the shutter starts to open, and the capacitor 13 is charged with the photocurrent of the light receiving element 12. The time for charging this capacitor 13 to a predetermined voltage depends on the brightness of the subject, and furthermore, this elapsed time corresponds to the aperture aperture. Therefore, for LV8 and above, comparator 1 is set when the predetermined aperture is reached, which is proportionally distributed between F5.61/3 and F8 depending on the brightness of the subject.
The output terminal of 6 becomes "L", and the gate signal is output from the AND circuit 20. This gate signal turns on the thyristor 5 to cause the flash discharge tube 6 to emit light, and also sets the flip-flop 23. When the flip-flop 23 is set, the gate signal is not output from the AND circuit 24 even if the shutter starts closing and the synchro switch 22 is turned on.

The flash discharge tube 6 continues to emit light until the terminal voltage of the capacitor 44 reaches the dimming level set by the variable resistor 39. Furthermore, LV14.5
In the above case, the shutter starts closing before the aperture reaches F8. At this time, since the synchro switch 2 turns on earlier than the transistor 19, the flash discharge tube 6 emits light at the aperture aperture determined by the shutter program diagram.

It can be said that it is desirable to use the light receiving elements 12, 31, and 53 in common in order to reduce costs.

FIG. 6 shows an embodiment in which automatic light adjustment is performed using a microcomputer.
A signal corresponding to the subject brightness is converted into a digital signal by an A/D converter 61 and then input to the microcomputer 60 . The desired dimming level is read out from the memory storing the relationship between the subject brightness and the dimming level, converted into an analog signal by the D/A converter 62, and then inputted to the comparator 41 shown in FIG. . When a signal indicating that the shutter opening operation has started is input, the microcomputer 60 measures time and outputs a strobe trigger signal (gate signal) when a time determined by the subject brightness has elapsed. The signal is sent to the gate of the thyristor 5 shown in FIG.

FIG. 7 shows an example of the relationship between the shutter opening time and the aperture diameter.

FIG. 8 shows the dimming level. For this dimming level, in the range of LV8 to 14.5, the light will emit light when the aperture reaches a predetermined aperture in the range of F4 1/3 to F8, and in the range of LV6 to 8, the aperture will be set to F2.8 to F4.
It emits light when the aperture reaches a predetermined aperture between 1/3, and for LV6 and below, it emits light when it reaches the maximum aperture of F2.8.

FIG. 9 shows the contents stored in the memory of the microcomputer in decimal notation.
When the LV value is specified, the delay time from when the shutter opening operation start signal is input until the strobe trigger signal is output and the dimming level are determined.
For example, at LV14.5, the delay time is 2.50ms and the dimming level (dimming F value) is F4. As a result, the strobe emits light when the shutter aperture reaches F8, and since the step difference (the difference between F8 and F4) is 2 stops, the proportion of strobe light that contributes to film exposure is 25%. If the light emission of the strobe is controlled according to the relationship shown in FIG. 9, the film exposure amount shown in FIG. 5 can be obtained.

Note that even if you set the strobe light emission timing to the closing action of the shutter between LV8 and LV16, and increase the dimming level as the LV value increases, the film exposure shown in Figure 5 will not occur. It is possible to do so.

According to the present invention having the above configuration, the proportion of strobe light contributing to film exposure increases as the brightness decreases during daytime synchronized photography.
When shooting indoors, in the morning, or in the evening, where the color temperature changes considerably, it is possible to record colors that are faithful to the subject without being affected by these scene lights.
Furthermore, the present invention is capable of proportionally controlled daytime synchronization photography that always maintains a predetermined ratio of strobe light and natural light that contribute to film exposure without being affected by subject brightness or shooting distance. .

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the strobe device of the present invention. FIG. 2 is a block diagram showing one embodiment of a shutter control device for use with the present invention. FIG. 3 is a shutter program diagram. FIG. 4 is a graph showing the dimming level. FIG. 5 is a graph showing the ratio of strobe light and natural light that contribute to film exposure during strobe photography. FIG. 6 is an explanatory diagram showing an embodiment using a microcomputer. FIG. 7 is an explanatory diagram showing the relationship between the shutter opening time and the aperture.
FIG. 8 is a graph showing the dimming level. FIG. 9 is a table showing the data stored in the microcomputer and the strobe light emission states corresponding thereto. 6...Flash discharge tube, 7...Light emitting thyristor,
8... Cutting off thyristor, 16, 33, 41...
Comparator, 22... Synchro switch, 31
... Light receiving element for measuring subject brightness, 33, 41
. . . comparator, 42 . . . phototransistor for measuring reflected light, 53 . . . light receiving element for measuring subject brightness, 58 . . . magnet for controlling exposure time, 62 .

Claims (1)

[Scope of Claims] 1. An automatic light control device that controls the amount of light emitted from a flash discharge tube, comprising: means for detecting subject brightness; when the subject brightness detected by the subject brightness detecting means is equal to or higher than a first brightness level, the subject brightness is detected by the subject brightness detecting means; means for causing the flash discharge tube to emit light when the aperture aperture determined according to the brightness is reached, and for causing the flash discharge tube to emit light when the shutter is fully opened or starts a closing operation when the brightness is below the first brightness level; When the brightness level is equal to or higher than the first brightness level, the light emission amount is set to a first dimming level that maximizes the amount of light emitted, and the first brightness level is
When the brightness level is lower than the brightness level of , and the brightness level is below a second brightness level at which natural light does not contribute to film exposure, a second brightness level lower than the first brightness level is set, and the second brightness level is lower than the first brightness level. and a second brightness level, the ratio of natural light and strobe light contributing to film exposure changes in inverse proportion. An automatic light control device comprising: means for integrating; and means for stopping light emission of the flash discharge tube when the integral value of the integrating means and the light control level reach a certain relationship. 2. The means for starting the light emission of the flash discharge tube measures the elapsed time after starting the shutter, and generates the first light emission start signal when the elapsed time reaches a time determined by the subject brightness. means to
means for generating a second light emission start signal when the shutter is closed or fully opened; when the brightness level is above the first brightness level, the first light emission start signal is extracted; when the brightness level is below the second brightness level, the second light emission start signal is generated; 2. The automatic light control device according to claim 1, further comprising means for extracting the second light emission start signal. 3. The first light emission start signal generating means includes a light receiving element for measuring subject brightness, a capacitor for integrating an electrical signal photoelectrically converted by this light receiving element, and determining whether a terminal voltage of this capacitor has reached a reference voltage. 3. The automatic light control device according to claim 2, comprising a comparator that performs the following. 4. An automatic light control device for controlling the amount of light emitted from a flash discharge tube, comprising: means for detecting subject brightness; and a point at which the subject brightness detected by the subject brightness detecting means exceeds a first brightness level and natural light no longer contributes to film exposure. 2 brightness levels and the first
Between the brightness levels, the flash discharge tube emits light when the aperture aperture determined according to the brightness of the subject is reached, and when the brightness level is below the second brightness level, the flash discharge tube emits light when the shutter is fully opened or starts closing. means for causing the flash discharge tube to emit light; when the brightness level is equal to or higher than the first brightness level, the flash discharge tube is set to a first dimming level at which the amount of light emission is maximum;
When the brightness level is below the brightness level, the light emission level is set to a second dimming level that minimizes the amount of light emitted, and between the first brightness level and the second brightness level, the ratio of natural light and strobe light that contributes to film exposure is set. means for setting a dimming level that changes in inverse proportion to the dimming level; means for photoelectrically converting and integrating reflected light from a subject illuminated with strobe light; and a constant relationship between the integral value of the integrating means and the dimming level. An automatic light control device comprising means for stopping the light emission of the flash discharge tube when the flash light discharge tube becomes light. 5. The means for starting the flash discharge tube to emit light includes:
The second step is to measure the time elapsed since the shutter starts opening, and the second step is to measure the time elapsed since the shutter starts opening. 5. The automatic light control device according to claim 4, further comprising the step of determining whether a time corresponding to the subject brightness has elapsed and generating a light emission start signal.