JP4033458B2 - Light control device for strobe - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a light control device for a strobe that adjusts the amount of light emitted from the strobe.
[0002]
[Prior art]
2. Description of the Related Art There is known a flash light control device used for an automatic light control type flash device, that is, a so-called auto flash device. The stroboscopic light control device receives the stroboscopic reflected light reflected by the subject during stroboscopic light emission, performs light amount integration, and stops stroboscopic light emission when the integrated amount reaches a predetermined level. As the light receiving element that receives the strobe reflected light, a light receiving element such as a photodiode or a phototransistor that passes a photocurrent according to the light intensity of the incident light is used. For example, a capacitor is charged with the photocurrent from the light receiving element. Thus, the light quantity integration is performed.
[0003]
[Problems to be solved by the invention]
By the way, it is desirable that the light receiving element used in the strobe light control device outputs a photocurrent without delay in response to the incidence of the strobe reflected light. However, when a phototransistor is used as the light receiving element, the inside A delay actually occurs under the influence of the parasitic capacitance. This delay time changes depending on the incident state of light until just before the phototransistor. For example, the delay time is usually about 5 μsec. However, in a situation where no light is incident until just before, the delay time is about twice. It will also become.
[0004]
The occurrence of the delay as described above has a problem that the light control accuracy is deteriorated by the delay amount because the light amount integration is not performed during the delay period although the strobe light is emitted. In particular, when the subject is at a short distance or when the photographing sensitivity is high, the strobe light emission becomes minute light emission, and the influence of the increase / decrease of the strobe light emission amount due to the delay becomes large. Further, since the delay time varies depending on the incident state of the light just before the phototransistion, the dimming accuracy varies.
[0005]
The present invention has been made in consideration of the above-described problems, and an object thereof is to provide a flash light control device capable of improving the light control accuracy.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, according to the first aspect of the present invention, there is provided a light source that illuminates a phototransistor by being lit, an external light measuring unit that measures the intensity of external light, and the external light measuring unit. And a light source control unit that turns on the light source just before the start of strobe light emission when the intensity of the measured external light is lower than a predetermined level and does not turn on the light source when the intensity is higher than the predetermined level .
[0007]
According to a second aspect of the present invention, the integrating means is an integrating capacitor that is charged with a photocurrent from a phototransistor, and the integration capacitor is prevented from being charged with a photocurrent from the phototransistor during lighting of a light source. Means are provided.
[0008]
According to the third aspect of the invention, the external light measuring means measures the intensity of the external light in response to the signal input corresponding to the half-press of the release button, and the light source control means is the external light measuring means by the external light measuring means. After measuring the light intensity, the light source is turned on when the external light intensity is lower than a predetermined level .
[0009]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows the configuration of an automatic light control strobe device embodying the present invention. The strobe device includes a strobe light emitting unit 3 and a light control unit 4 that is a light control device for the strobe. The strobe light emitting unit 3 includes a main capacitor that is charged prior to strobe light emission, a charging circuit that charges the main capacitor, an Xe tube that emits strobe light by discharging the main capacitor, and a trigger that is triggered by the input of a light emission start signal. A trigger circuit that starts discharging by applying a voltage to the Xe tube, a light emission stop circuit that stops strobe light emission by inputting a light emission stop signal, and the like.
[0010]
The dimming unit 4 includes a phototransistor 5, an integrating capacitor 6, a reference voltage generating circuit 7, a comparator 8, a light emitting diode 9, a switching element 10, a CPU 11, and the like. The phototransistor 5 receives the strobe light reflected by the subject and passes a photocurrent according to the light intensity. One terminal of the integrating capacitor 6 is connected to the emitter terminal of the phototransistor 5, and the integrating capacitor 6 is charged by the photocurrent from the phototransistor 5 during strobe light emission. The charging voltage of the integrating capacitor 6 is taken out as an integrating voltage Vs. Thereby, the light amount integration of the strobe reflected light received by the phototransistor 5 is performed, and the integrated value is output as the integrated voltage Vs.
[0011]
The integrated voltage Vs is input to one terminal of the comparator 8. The reference voltage Vref from the reference voltage generation circuit 7 is input to the other input terminal of the comparator 8, and the output signal of the comparator 8 is inverted at the moment when the integrated voltage Vs reaches the reference voltage Vref, and the signal level thereof is increased. It becomes “H level”, and this is sent to the strobe light emitting unit 3 as a light emission stop signal, and the strobe light emission is stopped.
[0012]
The light emitting diode 9 as the light source is turned on by the driver 15 under the control of the CPU 11 as the light source control means. The light emitting diode 9 is configured to irradiate the light receiving surface of the phototransistor 5 with light output from the light emitting diode 9. In this way, to irradiate the light receiving surface of the phototransistor 5 with the light of the light emitting diode 9, it may be either direct or indirect, but it is necessary not to prevent the phototransistor 5 from receiving the strobe reflected light. The light emitting diode 9 is lit until just before the strobe light is emitted. In this example, the light-emitting diode 9 is turned on in response to half-pressing of the release button 16 that is pressed for photographing, and is turned on until just before the strobe light is emitted.
[0013]
The switching element 10 serves as blocking means for blocking the integration capacitor 6 from being charged with the photocurrent from the phototransistor 5 while the light emitting diode 9 is lit. The switching element 10 is composed of, for example, a transistor, and is switched between an on state in which the emitter terminal of the phototransistor 5 is connected to the ground and a disconnected off state under the control of the CPU 11.
[0014]
The switching element 10 is turned on while the light emitting diode 9 is lit, and is turned off during other periods. This prohibits the integration capacitor 6 from being charged by the photocurrent from the phototransistor 5 that flows with the light of the light emitting diode 9 before the strobe light emission, and the light from the phototransistor 5 on which the strobe reflected light is incident during the strobe light emission. The integration capacitor 6 is allowed to be charged with current. The switching element 10 also has a function of discharging the charge accumulated in the integrating capacitor 6 by the previous strobe light emission by being turned on before the strobe light emission.
[0015]
The release button 16 is pressed during shooting. The release button 16 can be operated to a half-pressed position and further to a fully-pressed position, and a release signal corresponding to each position is sent to the CPU 11. When the release button 16 is set to the half-pressed position, preparatory operations for photographing, for example, measurement of the distance to the subject and measurement of the subject brightness, that is, distance measurement and photometry, are performed. After the focusing operation is performed, an exposure mechanism (not shown) is operated based on the photometric result to perform exposure. The exposure mechanism sends a sync signal to the CPU 11 when the shutter is fully opened.
[0016]
When the CPU 11 receives the release signal corresponding to the half-pressed position of the release button 16, the CPU 11 turns on the light emitting diode 9 through the driver 15 and turns on the switching element 10. Hold until the pressure is released or a sync signal is input.
[0017]
Further, when the release button 16 receives the release signal corresponding to the fully pressed position, the CPU 11 performs exposure by operating the exposure mechanism after completing the focusing operation of the photographing lens. When a sync signal from the exposure mechanism is input to the CPU 11 during this exposure, the CPU 11 turns off the light emitting diode 9 and turns off the switching element 10, and then sends a light emission start signal to the strobe light emitting unit 3 to emit strobe light. To do.
[0018]
Next, the above configuration will be described with reference to FIG. If the release button 16 is pressed halfway for shooting, distance measurement and photometry are performed. At the same time, the CPU 11 turns on the light emitting diode 9 via the driver 15 and turns on the switching element 10.
[0019]
The phototransistor 5 is irradiated with light from the light-emitting diode 9 that is turned on, and a photocurrent flows from the phototransistor 5. Since the photocurrent from the phototransistor 5 does not flow to the integrating capacitor 6 because the switching element 10 is turned on, the integrating capacitor 6 is not charged. The electric charge accumulated in the integrating capacitor 6 until then is discharged by turning on the switching element 10.
[0020]
When the release button 16 is further pushed down and fully pressed, the exposure lens is operated based on the previous distance measurement result, and then the exposure mechanism is operated to perform exposure. The sync signal is input to the CPU 11 by the exposure mechanism at the moment when the shutter is fully opened during this exposure. Upon receiving this sync signal, the CPU 11 extinguishes the light emitting diode 9 at that moment and turns off the switching element 10 and then sends a light emission start signal to the strobe light emitting unit 3.
[0021]
When the light emission start signal is input, the strobe light emission unit 3 starts strobe light emission, and the strobe light is emitted toward the subject. Then, a part of the strobe reflected light reflected by the subject enters the phototransistor 5, and a photocurrent corresponding to the light intensity flows. The photocurrent flowing at this time flows to the integrating capacitor 6 and charges it because the switching element 10 is in the OFF state. As a result, the charging voltage of the integrating capacitor 6, that is, the integrating voltage Vs rises.
[0022]
When the strobe reflected light is received and the integrated voltage Vs further rises and reaches the reference voltage Vref, the output signal of the comparator 8 is inverted to “H level”. The inversion to the “H level” is sent to the strobe light emitting unit 3 as a light emission stop signal, so that the strobe light emission is stopped.
[0023]
FIG. 3 shows an example of a change in the integrated voltage Vs. For example, when the light emitting diode 9 is not turned on before strobe light emission in a dark place, the integrated voltage Vs rises greatly delayed from the start of strobe light emission due to the junction capacitance of the phototransistor 5 as shown by the broken line in the figure. To start. For this reason, the exposure amount becomes excessive by the amount that the light amount integration is not performed. Here, the excessive exposure amount is the exposure amount during the delay time, but since the intensity of the strobe reflected light changes depending on the shooting conditions and the delay time is not constant, the excessive exposure amount varies. For example, the reference voltage Vref cannot be corrected in advance so that the amount does not become excessive. As a result, in the case where the light emitting diode 9 is not turned on, the light control accuracy is deteriorated. In particular, when the subject is at a short distance or when the photographing sensitivity is high, since the light emission is minute, the influence of the excessive exposure amount is increased and the light control accuracy is significantly reduced.
[0024]
However, in the present invention, the light emitting diode 9 is turned on until just before the strobe light emission starts as described above, and the photodiode 5 is irradiated with light from the light emitting diode 9. For this reason, the delay due to the junction capacitance hardly occurs, and as shown by the solid line in the figure, the integrated voltage Vs starts to rise with a small delay from the start of light emission. As a result, the period during which the light amount integration is not performed is shortened, and accordingly, the excessive exposure amount becomes extremely small. As a result, it is possible to perform dimming with high accuracy even in a situation where minute light emission occurs.
[0025]
Actually, when the strobe light emission is stopped, the increase of the integrated voltage Vs is stopped accordingly, but FIG. 3 shows the change of the integrated voltage Vs when the strobe light emission is continued.
[0026]
FIG. 4 shows an example in which a sensor for detecting ambient brightness is provided. In addition, except being demonstrated below, it is the same as the said embodiment, The same code | symbol is attached | subjected to the same structural member, and the description is abbreviate | omitted.
[0027]
A light receiving element 20 is provided as external light measuring means for detecting the intensity of external light incident on the phototransistor 5. As the light receiving element 20, a phototransistor, a photodiode, CdS, or the like can be used. Further, for example, photometric means for measuring subject luminance may be used to determine the exposure value, or the light intensity of external light may be detected from the magnitude of the photocurrent from the phototransistor 5. Furthermore, in a digital camera or the like, the light intensity of external light may be detected based on the output of an image sensor that performs shooting.
[0028]
When the release button 16 is half-pressed, the CPU 11 measures the light intensity of the external light incident on the phototransistor 5 using the light receiving element 20, and when the light intensity of the external light is equal to or higher than a predetermined level, If the light emitting diode 9 is not turned on and is below a predetermined level, the light emitting diode 9 is controlled to turn on until just before the strobe light emission, as in the above embodiment. According to this, the light emitting diode 9 is not turned on when the outside light is incident on the phototransistor 5 so that the delay time is sufficiently short in a bright place, and the light is not dark when the delay time is increased. In addition, since the light emitting diode 9 is turned on, power consumption can be reduced.
[0029]
In each of the above embodiments, a capacitor is used as the integration means. However, the integration amount is not limited to the capacitor, and the integration amount may be obtained by calculation based on each result of periodically sampling the magnitude of the photocurrent. Moreover, when performing strobe light emission, you may light a light emitting diode like said each embodiment. Further, as the light source, other things such as a lamp may be used instead of the light emitting diode.
[0030]
【The invention's effect】
As described above in detail, according to the light control device for strobe of the present invention, the light source is turned on until just before the start of strobe light emission, and the phototransistor is irradiated with light to improve the delay caused by the junction capacitance. Even when the strobe emits a small amount of light, high light control accuracy can be obtained.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of an automatic light control type strobe device embodying the present invention.
FIG. 2 is a timing chart showing a light emission timing relationship between a light emitting diode and strobe light emission.
FIG. 3 is a graph showing a difference in change in integrated voltage depending on whether or not a light emitting diode is turned on.
FIG. 4 shows an example of controlling whether or not a light emitting diode is turned on according to the intensity of external light.
[Explanation of symbols]
3 Strobe light emitting unit 4 Dimming unit 5 Photodiode 6 Integrating capacitor 10 Switching element 11 CPU

Claims (3)

A phototransistor for passing a photocurrent according to the intensity of the strobe reflected light and an integrating means for performing light amount integration based on the photocurrent from the phototransistor. When the integrated value by the integrating means reaches a predetermined level, the strobe In the light control device for the strobe that outputs the light emission stop signal for stopping the light emission,
When the light source illuminates the phototransistor by illuminating, the external light measuring means for measuring the intensity of the external light, and the intensity of the external light measured by the external light measuring means is lower than a predetermined level And a light source control unit that turns on the light source until immediately before the start of strobe light emission and does not turn on the light source when the light level exceeds a predetermined level .   The integrating means is an integrating capacitor that is charged with a photocurrent from the phototransistor, and includes a blocking means for preventing the integrating capacitor from being charged with a photocurrent from the phototransistor during lighting of the light source. The light control device for a strobe according to claim 1. The external light measurement means measures the intensity of external light in response to a signal input corresponding to a half-press of the release button, and the light source control means is configured to measure the external light intensity by the external light measurement means. The light control device for a strobe according to claim 1 or 2 , wherein the light source is turned on when the intensity of external light is lower than a predetermined level .

Images