JP2004077889A - Automatic electronic flash unit and camera - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an automatic electronic flash unit and a camera which have a wide range of measurable luminance, can be simplified in circuit constitution and reduced in arrangement space for a light receiving element, and have good response to follow up even a startup of large-output electronic flash light abruptly varying in quantity well. <P>SOLUTION: An LED 2 or photodiode is used as the light receiving element of the automatic electronic flash unit for the camera. After a voltage based upon the photovoltaic force of the light receiving element is amplified by a MOSFET 9, a capacitor 17 for integration is charged through an amplifying resistance element 11 and a transistor 15 for integration. When the charging voltage of the capacitor 17 for integration exceeds a reference voltage, a comparator 41 turns off a discharge tube 20. <P>COPYRIGHT: (C)2004,JPO

Description

【０１３２】
次に、上述した構成のカメラで、外光輝度が存在する状況下で、ストロボ光を利用する場合である、所謂ミックス光の場合の参照電圧の設定の仕方について説明する。
【０１３３】
ストロボ光を使用せず外光輝度のみの状況下での、カメラの露出量をＥＶ（Ｅｌｅｃｔｒｏｎ　Ｖｏｌｔｏ）とする。この外光輝度露出量がたとえば８０％とすると、不足する露出量ΔＥＶは、下記式７で演算され、−０．３２となる。
【０１３４】
ΔＥＶ　＝　ｌｏｇ０．８／ｌｏｇ２＝−０．３２　・・・式７
【０１３５】
不足する２０％の露出をストロボ光で補う場合、ΔＧＶは、下記式８で演算され、−２．３２となる。
【０１３６】
ΔＧＶ　＝　ｌｏｇ０．２／ｌｏｇ２＝−２．３２　・・・式８
【０１３７】
そして、ΔＧＶ＝−２．３２なので、参照電圧は、式４を含む下記式群９で演算できる。ここで、ΔＧＶがマイナスなので式４のＶｒｅｆ’とＶｒｅｆとが逆になる。外光輝度のみの参照電圧をＶｒｅｆ’とし、ストロボ光を利用するときの参照電圧をＶｒｅｆとすると、ＶｒｅｆはＶｒｅｆ’の２０％となる。したがって、外光輝度のみを利用する場合の参照電圧が１Ｖであったなら、２０％のストロボ光の参照電圧としては０．２Ｖを使用する。
【０１３８】
ｌｏｇ（Ｖｒｅｆ／Ｖｒｅｆ’）／ｌｏｇ２　＝　ΔＧＶ＝−２．３２
Ｖｒｅｆ／Ｖｒｅｆ’　＝　１０^{−０．６９８}＝０．２
∴　Ｖｒｅｆ　＝　０．２Ｖｒｅｆ’　　　　　　　　　　　　・・・式群９
【０１３９】
なお、ストロボ光の露出量への寄与率をＸとした場合、一般式として下記式群１０で、参照電圧を求めることができる。但し、ストロボ光が１００％の露出を与えるＶｒｅｆ１が、１Ｖとする。
【０１４０】
Ｘ　＝　１−１０^{ΔＥＶ×ｌｏｇ２}
ΔＧＶ　＝　ｌｏｇ（Ｘ）÷ｌｏｇ２
Ｖｒｅｆ　＝　１０^{ｌｏｇ２×ΔＧＶ}　　　　　　　　　　・・・式群１０
【０１４１】
以上のように、この実施の形態１にかかるカメラでは、ＬＥＤ２を点滅させることで、セルフタイマを用いた撮像時に、撮像ボタン６１を操作した後の待ち状態を表示することができる。また、ＬＥＤ２の受光光量に基づいて、非常にダイナミックレンジが広いＢＶ値を検出することができる。すなわち、外光の測光が可能となる。さらに、ストロボ光の反射光をＬＥＤ２で受光し、ストロボ光のみの測光を可能としている。また、このＬＥＤ２の受光光量の総和値に基づいて、ストロボ光の被写体による反射光量の総和値を制御することもできる。さらに、外光の測光とストロボ光のみの測光とを可能とすることによってミックス光領域を含む全てのストロボ使用領域における高精度な制御を可能としている。
【０１４２】
特に、ＭＯＳＦＥＴ９と積分用ＰＮＰトランジスタ１５との間に直流カットコンデンサ１３を設けているので、積分用ＰＮＰトランジスタ１５は、ＬＥＤ２の光起電力の変化分のみに基づいて積分用コンデンサ１７を充電することとなる。したがって、周囲の環境が明るい状態であっても、不足する被写体の光量を適切に補うように、ストロボ光を発光させることができる。また、ストロボ光を受光する受光素子としてＬＥＤ２を使用しているので、フォトトランジスタを受光素子として使用した場合よりも、積分用コンデンサ１７の充電電圧は、実際のストロボ光の総発光光量により良く追従する。その結果、フォトトランジスタを受光素子として使用した場合よりも、不足する光量を正確に補うことができる。
【０１４３】
また、１つのＬＥＤ２を用いて、露出計算用の露出量と、ストロボ光の被写体による反射光量の総和値とを検出しているので、従来のようにこれらをフォトトランジスタとＣｄＳ受光セルとの組み合わせて検出する場合のように、受光素子同士の受光特性誤差を考慮する必要がない。その結果、たとえばＬＥＤ２の周囲が明るい状況下でストロボ光を発光させるような、所謂ミックス光のトータルの露出量を、より正確に制御することができる。
【０１４４】
このように、この実施の形態１にかかるカメラでは、発光素子としてのＬＥＤ２を用いて、オート撮像モードでの周囲の光量を検出し、且つ、ストロボ光の被写体による反射光量の総和値を検出することができる。したがって、従来のカメラでは、たとえば、セルフタイマ用の発光素子と、周囲の光量を検出するＣｄＳ受光セルと、ストロボ光の光量を検出するフォトトランジスタと、を別々に用いていたが、これらを全て１つのＬＥＤ２で兼用することができる。なお、上述の３つの機能を１つのＬＥＤ２でまかなうのではなく、被写体の測光とストロボ光の反射光量の検出の２つの機能をＬＥＤ２で兼ね、セルフタイマ用の発光素子は他のものを付加する構成としたりして、３つの機能のうちいずれか２つをＬＥＤ２で兼用するようにしてもよい。
【０１４５】
その結果、カメラに設けるセンサの個数が削減され、カメラの小型軽量化、デザインの自由度の向上、故障率の低減などの効果を得ることができる。また、値段の安いカメラであっても、少ない部品点数で高機能なカメラを実現することができる。特に、ＬＥＤ２で検出したＢＶ値を用いて、カメラの絞りやシャッタスピードを設定しているので、トータルとしてのコスト上昇を抑えることができる。
【０１４６】
この実施の形態１に係るカメラでは、本来は発光素子であるＬＥＤ２を、受光素子としても利用している。その結果、ＬＥＤ２の発光方向や発光範囲がそのまま、光量検出方向や光量検出範囲となる。周囲の光量を検出するＣｄＳ受光セルや、ストロボ光の光量を検出するフォトトランジスタをカメラに使用する場合には、それぞれの受光素子についてその光量検出方向や光量検出範囲を設計をしなければならない。しかも、各受光素子毎に、レイアウトが異なるカメラの試作品を多数作成し、各試作品での受光方向や受光範囲を１つずつ測定しなければならなかった。しかしながら、この実施の形態１であれば、単にＬＥＤ２を点灯させてその照射角や照射範囲を測定するだけで、簡単に受光角や受光範囲の測定が可能となる。その結果、受光素子としてのＬＥＤ２や、ＬＥＤ２の前面の図示外の受光レンズの受光角などを簡単に修正することができ、カメラの設計期間が非常に短縮され、試作費用が削減される。
【０１４７】
また、上述した実施の形態１によれば、使用絞り値（Ｆ値）の情報が得られれば、カメラの露出制御方法がプログラムシャッタであっても、絞り優先シャッタであっても利用できるものとなる。また、メカシャッタに限らず、ＣＣＤなどの電子シャッタを使用するカメラにも適用できる。
【０１４８】
なお、上述の実施の形態は、本発明の好適な実施の形態であるが、これに限定されるものではなく、本発明の要旨を逸脱しない範囲において、種々の変形、変更が可能である。たとえば、ＬＥＤ２の代わりにフォトダイオードを使用してもよい。
【０１４９】
上記実施の形態１では、シャッタを開くのと同時にストロボ光を発光させ、ストロボ光の被写体による反射光量の総和値が所定の光量の総和値に達すると、シャッタを閉じる動作を行わせている。この他にもたとえば、予め被写体との距離がＡＦ機能などに基づいて測定されているような場合には、シャッタを閉じるタイミングを基準として、その基準時刻までにストロボ光の被写体による反射光量の総和値が所望の光量の総和値となるように、シャッタの閉じ時刻よりも所定の時間だけ早くストロボ光を発光させるようにしてもよい。これにより、シャッタが開いている期間におけるストロボ光の被写体による反射光量の総和値を、同様に制御することができる。
【０１５０】
上記実施の形態１では、Ａ点の電圧は、そのままマイクロコンピュータ４３に入力されている。この他にもたとえば、Ａ点とマイクロコンピュータ４３との間にコンデンサを設けてもよい。これにより、他のカメラのストロボ光が光っているような状況下であっても、正確な被写体の平均的なＢＶ値を検出することができる。
【０１５１】
上記実施の形態１では、参照電圧用コンデンサ５２を充電することで、参照電圧を生成している。この他にもたとえば、銀塩フィルムやＣＣＤの感度に対応した抵抗素子群と、絞り値に対応した抵抗素子群とを設け、この中から適切な抵抗素子の組み合わせを選択する制御を行うことで、参照電圧を生成してもよい。
【０１５２】
但し、この変形例のように抵抗素子の組み合わせることで参照電圧を生成する場合には、使用する抵抗素子の個数が多くなってしまう。したがって、実施の形態１のほうが、構成が簡素である。しかも、この変形例に比べて、実施の形態１のほうが、任意の電圧を高精度に且つ細かく設定することができるので、ミックス光などの制御などにおいては、ＬＥＤ２の追従性の良さを生かして、正確な光量の制御が可能となる。さらに、実施の形態１のほうが、ストロボ光の被写体による反射光量の総和値として、ＢＶ値の１段以下の制御が可能となるので、受光感度のラティテュードが低い（ダイナミックレンジが狭い）ＣＣＤで撮像する場合であっても、光量を適切に補正して高品位の画質の画像を撮像することができる。
【０１５３】
【発明の効果】
本発明では、受光素子としてフォトダイオードあるいはＬＥＤを使用しているので、受光素子としてフォトトランジスタを使用した場合に比べて、測定可能な輝度の範囲が広くなる。しかも、回路構成が簡単化できるとともに受光素子の配置スペースを小さくできる。また、本発明では、受光素子としてフォトダイオードあるいはＬＥＤを使用しているので、急激に光量が増減する大出力のストロボ光の立ち上がりに対しても良く追従し、受光素子としてフォトトランジスタを使用した場合に比べて、応答性が改善される。
【図面の簡単な説明】
【図１】本発明の実施の形態１に係るオートストロボ回路が組み込まれたカメラの回路図である。
【図２】図１中の第二の増幅抵抗素子に発生する電圧（Ｖ）と、受光素子となるＬＥＤの受光光量との関係に基づいて、Ａ点の電圧と、ＢＶ値とを対応付けた場合の一例を示す輝度特性図である。
【図３】図１中のストロボ回路をフル発光させたときに、Ａ点の電圧（第二の増幅抵抗素子に発生する電圧）の時間変化と、Ｂ点の電圧（第三の増幅抵抗素子に発生する電圧）との時間変化を示す特性図である。
【図４】図１中のマイクロコンピュータの制御フローを説明するフローチャートである。
【図５】図１中の積分用コンデンサの充電電圧の時間特性図である。
【符号の説明】
２　ＬＥＤ（受光素子）
５　第二の分圧抵抗素子（バイアス抵抗素子）
６　切替用ＰＮＰトランジスタ（切替用トランジスタ）
９　ＭＯＳ型電界効果トランジスタ（ＭＯＳＦＥＴ、増幅トランジスタ）
１１　第二の増幅抵抗素子（増幅抵抗素子）
１２　第三の増幅抵抗素子（並列抵抗素子）
１３　直流カットコンデンサ
１５　積分用ＰＮＰトランジスタ（積分用トランジスタ）
１７　積分用コンデンサ
２０　キセノン放電管（放電管）
４１　コンパレータ
４２　参照電圧回路
４３　マイクロコンピュータ
５１　参照電圧用ＰＮＰトランジスタ（参照電圧用トランジスタ）
５２　参照電圧用コンデンサ[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an automatic strobe device and a camera that output strobe light by causing a discharge tube to emit light.
[0002]
[Prior art]
The auto strobe device is for supplementing the light amount from the subject when the light amount is insufficient. This auto strobe device emits strobe light from a xenon discharge tube or the like in synchronization with the opening of a shutter of a camera. Further, the auto strobe device receives strobe light reflected from a subject by a phototransistor, and stops emitting strobe light when the received light amount reaches a desired light amount.
[0003]
The phototransistor obtains a collector current proportional to the amount of received light, and by simply integrating this collector current with a capacitor, the total value of the amount of strobe light reflected by the subject can be detected. Therefore, an auto strobe device can be configured at a lower cost than a photodiode in which an operational amplifier must be used to amplify the output.
[0004]
When the auto strobe device compensates for the light amount from the subject, the camera can capture an image with an appropriate exposure amount.
[0005]
[Problems to be solved by the invention]
However, a conventional auto strobe device uses a phototransistor as a means for receiving reflected light of a strobe light from a subject. This phototransistor has a narrow dynamic range for luminance (a range of measurable luminance).
[0006]
Therefore, in a conventional camera, a CdS light receiving cell or the like is provided as a photometric element separately from a phototransistor for measuring the amount of strobe light reflected from a subject. The aperture and shutter speed are calculated based on the detected value of the CdS light receiving cell. Since a plurality of light receiving elements are provided as described above, the circuit configuration becomes complicated, and a large space for arranging the light receiving elements must be secured, which is disadvantageous for miniaturization.
[0007]
Although the phototransistor has a quick response characteristic as compared with a CdS light receiving cell or the like, the response speed is slightly slow in order to accurately measure the amount of strobe light reflected by the subject. In particular, the ability to follow the rising edge of a high-output strobe light whose light intensity increases or decreases rapidly is poor. Therefore, the detection value of the light amount output from the phototransistor becomes smaller than the detection value corresponding to the light amount actually received by the phototransistor, and the strobe light tends to be excessive.
[0008]
The present invention has been made to solve the above-described problems, and relates to an auto strobe device and a camera that have a wide range of measurable luminance, can simplify a circuit configuration, and can reduce an arrangement space of a light receiving element. Things. The present invention also relates to an auto-flash device and a camera with good responsiveness, which well follow the rising of high-power strobe light whose light amount rapidly increases and decreases.
[0009]
[Means for Solving the Problems]
An auto strobe device according to the present invention is an auto strobe device that outputs strobe light by causing a discharge tube to emit light. In the auto strobe device, a light receiving element including a photodiode or an LED that receives reflected light of an object such as a strobe light, and a light receiving element A bias resistor for applying a bias voltage to the cathode electrode of the transistor, an amplifying transistor having the anode electrode of the light receiving element connected to the gate terminal, an amplifying resistor connected to the drain terminal of the amplifying transistor, and a high voltage of the amplifying resistor The more integrated the transistor, the higher the collector current, the higher the integration capacitor that is charged by the collector current, the higher the reference voltage circuit that outputs the reference voltage, and the comparator that compares the charging voltage of the integration capacitor with the reference voltage. And the comparator has an integration capacitor that is higher than the reference voltage. If it is determined that the charging voltage of the sub is increased, it is to turn off the discharge tube.
[0010]
With this configuration, the LED or the photodiode as the light receiving element is biased by the bias resistance element and connected to the amplification transistor. Therefore, the minute voltage generated in the LED or the photodiode by the photoelectromotive force is surely amplified by the amplification transistor and becomes the voltage of the amplification resistance element.
[0011]
By the way, the voltage due to the photoelectromotive force generated in the LED or the photodiode changes logarithmically with respect to the amount of received light. When the voltage at the base terminal of the integrating transistor changes, the collector current increases exponentially. Therefore, the collector current has a relationship proportional to the amount of light received by the LED or photodiode. The voltage generated in the integrating capacitor is also a voltage proportional to the amount of light received by the LED or the photodiode. Moreover, the rate of change of the voltage with respect to the amount of received light can be set arbitrarily. When the charging voltage generated in the integrating capacitor becomes higher than the reference voltage, the discharge tube is turned off.
[0012]
Therefore, with this configuration, the measurable luminance range (dynamic range) can be widened. As a result, the auto strobe device according to the present invention not only can detect the brightness from weak strobe light to strong strobe light, but also can detect the brightness under any shooting environment from a dark room to outdoors.
[0013]
In addition, with this configuration, since the LED or the photodiode has better responsiveness than the phototransistor, a voltage that changes following the rising edge of a high-output strobe light whose light amount rapidly increases or decreases is detected. be able to. As a result, in the first embodiment, the total exposure amount of a CCD (Charge Coupled Device) or a silver halide film can be controlled more accurately than when a phototransistor is used.
[0014]
The auto strobe device according to the present invention further includes a parallel resistance element and a DC cut capacitor connected in series with the parallel resistance element, and the parallel resistance element and the DC cut capacitor are entirely in parallel with the amplification resistance element. And a connection point between the parallel resistance element and the DC cut capacitor is connected to the base terminal of the integrating transistor.
[0015]
With this configuration, it is possible to apply, to the base terminal of the integrating transistor, a voltage in which the voltage based on the bias voltage applied to the LED or the photodiode is canceled. Therefore, despite the presence of the bias voltage, the charging voltage of the integrating capacitor is directly proportional to the amount of light received by the LED or photodiode.
[0016]
Further, even when the surroundings of the LED are bright and a voltage is constantly generated in the LED or the photodiode, a voltage obtained by canceling the steady voltage is applied to the base terminal of the integrating transistor. Can be. Therefore, the charging voltage of the integrating capacitor is directly proportional to the amount of light received by the LED or photodiode, even if the area around the LED or photodiode is bright.
[0017]
As a result, based on the charging voltage of the integrating capacitor, which is proportional to the total amount of strobe light reflected by the subject, the total value of the strobe light reflected by the subject and, consequently, the total exposure of the CCD and film is calculated. Can be precisely controlled. In particular, even in the case where the strobe light is emitted in a bright environment around the LED or the photodiode, a voltage corresponding to the light amount of only the strobe light can be generated in the integrating capacitor. It is possible to accurately control the total value of the amount of light reflected by the subject.
[0018]
The auto strobe device according to the present invention further includes control means for detecting a voltage generated in the amplifying resistance element and setting a reference voltage calculated from the detected voltage as a BV value in a reference voltage circuit.
[0019]
With this configuration, a BV value is detected using an LED or a photodiode for detecting the amount of strobe light reflected by a subject, and a reference voltage is calculated using the BV value.
[0020]
Therefore, unlike the case where the detection value used for exposure calculation is detected using a CdS light receiving cell provided separately from the light receiving element, it is not necessary to consider a light receiving characteristic error between the light receiving elements.
[0021]
As a result, it is possible to more accurately control the total exposure amount of so-called mixed light, for example, to emit strobe light under a situation where the periphery of the LED or the photodiode is bright.
[0022]
Moreover, the aperture and shutter speed of the camera can be set using the BV value detected by the LED or the photodiode. As a result, a CdS light receiving cell or the like becomes unnecessary, and a cost increase of the camera as a whole can be suppressed.
[0023]
The auto strobe device according to the present invention further comprises a reference voltage circuit, a reference voltage capacitor, and a reference voltage transistor having a collector terminal connected to the reference voltage capacitor, and an amplifying resistor element and a DC cut capacitor. And a control means for setting a reference voltage calculated as a BV value in the reference voltage circuit in the reference voltage circuit.
[0024]
With this configuration, the number of elements used can be significantly reduced as compared with the case where a reference voltage is generated by a combination of resistance elements. In addition, compared to the case where a reference voltage is generated by a combination of resistive elements, an arbitrary voltage can be set with high precision and fineness. Taking advantage of this advantage, it is possible to accurately control the total value of the amount of strobe light reflected by the subject. Further, since it is possible to control the BV value as one step or less as the total value of the amount of reflected strobe light by the subject, even if the image is taken by a CCD having a low latitude of light receiving sensitivity (a narrow dynamic range), By appropriately correcting the amount of light, a high-quality image can be captured.
[0025]
The auto strobe device according to the present invention further comprises an LED as a light receiving element, a switching transistor having a collector terminal connected to the anode electrode of the LED, and control means for controlling the switching transistor to be turned on and off. is there.
[0026]
With this configuration, the LED serving as the light receiving element can be made to emit light by controlling the switching transistor to the ON state. Then, simply by measuring the irradiation angle and the irradiation range of the LED, it is possible to easily measure the light receiving angle and the light receiving range as the light receiving element. As a result, the LED as the light receiving element, the light receiving angle of the light receiving lens in front of the LED, and the like can be easily corrected, so that the design period of the camera is greatly shortened, and the cost of the prototype is reduced.
[0027]
Further, by controlling the switching transistor to be turned on and off at the time of the self-timer, the LED serving as the light receiving element can be made to blink, and the waiting time and the timing of opening the shutter can be notified to the person who is the subject.
[0028]
Another auto-strobe device according to the present invention is an auto-strobe device that outputs strobe light by causing a discharge tube to emit light. The auto-strobe device has a light-receiving element made up of a photodiode or an LED that receives strobe light reflected from a subject or the like. The light receiving element includes a light receiving control circuit that enables photometry of external light and photometry of strobe light only.
[0029]
If this configuration is adopted, photometry of external light and photometry of only strobe light can be measured by one light receiving element and one light receiving control circuit. As a result, the number of light receiving elements provided in the camera can be reduced.
[0030]
A camera according to the present invention includes any one of the above-described auto strobe devices.
[0031]
If this configuration is adopted, the range of measurable luminance (dynamic range) is widened, and it is possible not only to detect the luminance from weak strobe light to strong strobe light, but also in all shooting environments from dark rooms to outdoors. Can be detected. In addition, the response of the light-receiving element is better than that of a phototransistor, and it follows the rising edge of high-power strobe light, where the amount of light rapidly increases and decreases. Can be accurately controlled.
[0032]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an auto strobe device and a camera according to the present invention will be described with reference to the drawings.
[0033]
Embodiment 1 FIG.
FIG. 1 is a circuit diagram of a camera incorporating an auto strobe device according to Embodiment 1 of the present invention. The circuit diagram of the camera shown in FIG. 1 shows a strobe circuit and peripheral circuits, and other functional parts required for controlling the camera are omitted or simplified. Further, the circuit shown in FIG. 1 is a light receiving element control circuit which enables photometry of external light and photometry of only strobe light by a light receiving element described later.
[0034]
The camera incorporating the auto strobe device according to the first embodiment includes a power storage member 1 such as a battery that outputs a DC voltage from a positive terminal and a negative terminal, and an LED (Light Emitting Diode) 2 as a light receiving element. . The negative terminal of the power storage member 1 is connected to a frame ground 3 such as a camera frame.
[0035]
Between the positive terminal and the negative terminal of the power storage member 1, a first voltage dividing resistance element 4 and a second voltage dividing resistance element 5 as a bias resistance element are connected in series. The cathode electrode of the LED 2 is connected between the two voltage dividing resistance elements 4 and 5. As a result, a bias voltage is applied to the cathode electrode of LED2.
[0036]
A switching PNP transistor 6 as a switching transistor is connected between the plus terminal of the power storage member 1 and the anode electrode of the LED 2. The collector terminal of the switching PNP transistor 6 is connected to the anode electrode of the LED 2. A first control resistance element 7 is connected between the emitter terminal and the base terminal of the switching PNP transistor 6, and one end of a second control resistance element 8 is connected to the base terminal.
[0037]
Therefore, for example, when the other end of the second control resistance element 8 is set to the same level as the frame ground 3, a voltage is generated in the first control resistance element 7 and the second control resistance element 8, and the switching PNP transistor 6 turns on. The LED 2 emits light by the current flowing from the emitter terminal to the collector terminal of the switching PNP transistor 6 in the ON state.
[0038]
The smaller the voltage generated in the voltage dividing resistance element 5 between the cathode electrode of the LED 2 and the minus terminal of the power storage member 1, the higher the brightness of the LED 2. When the LED 2 is used as a light-emitting element for a self-timer, for example, the brightness of the LED 2 is set so that it can be confirmed that the LED 2 is lit from a position several meters away in a bright state. What is necessary is just to select the resistance value of the second voltage dividing resistance element 5.
[0039]
Conversely, for example, when the other end of the second control resistance element 8 is set to the same level as the positive terminal of the power storage member 1, no voltage is generated in the first control resistance element 7 and the second control resistance element 8. Therefore, the switching PNP transistor 6 is turned off. In the off state, no current flows from the emitter terminal to the collector terminal of the switching PNP transistor 6, so that the LED 2 is turned off.
[0040]
The light emission response speed of the LED 2 is about 100 ns (nanosecond). Therefore, when the switching PNP transistor 6 is turned on / off, the LED 2 is switched between a light-on state and a light-off state suitably following the control.
[0041]
By the way, when light is applied to the PN junction of a semiconductor light emitting element such as the LED 2 that emits light by applying a voltage, a potential difference is generated between the P-type semiconductor and the N-type semiconductor. This phenomenon is called photovoltaic.
[0042]
Therefore, in the camera control device according to the first embodiment, the gate terminal of the MOS field effect transistor (MOSFET) 9 as an amplification transistor is connected to the anode electrode of the LED 2. The source terminal of the MOSFET 9 is connected to the frame ground 3 via the first amplification resistance element 10. The drain terminal of the MOSFET 9 is connected to the plus terminal of the power storage member 1 via a second amplification resistance element 11 as an amplification resistance element.
[0043]
The MOSFET 9 is turned on when the potential of the gate terminal becomes higher than the potential of the source terminal by a predetermined voltage. In the MOSFET 9 in the ON state, a current flows between the source terminal and the drain terminal. Due to this current, a voltage is generated in the second amplification resistance element 11. Further, as the potential difference between the potential of the gate terminal and the potential of the source terminal increases, the current flowing between the source terminal and the drain terminal increases, and the voltage generated in the second amplification resistance element 11 also increases.
[0044]
Conversely, when the potential difference between the potential of the source terminal and the potential of the gate terminal becomes smaller than a predetermined potential, the MOSFET 9 is turned off. In the MOSFET 9 in the off state, no current flows between the source terminal and the drain terminal.
[0045]
In the first embodiment, the gate terminal of the MOSFET 9 is connected between the first voltage dividing resistance element 4 and the second voltage dividing resistance element 5 via the LED 2. Therefore, the MOSFET 9 is basically turned on. Then, a voltage is generated in the second amplifying resistance element 11 by a current flowing between the source terminal and the drain terminal of the MOSFET 9 in the ON state.
[0046]
In the first embodiment, the LED 2 is connected between the second voltage-dividing resistance element 5 and the gate terminal of the MOSFET 9. Therefore, when a voltage due to photovoltaic voltage is generated in the LED 2, the potential of the gate terminal of the MOSFET 9 changes with the voltage generated in the LED 2. When the potential of the gate terminal of the MOSFET 9 changes, the voltage of the second amplification resistance element 11 also changes.
[0047]
By the way, the relationship between the amount of light received by the LED 2 and the voltage due to the photoelectromotive force has substantially the same characteristic relationship as the relationship between the voltage applied to the photodiode and the amount of light emitted from the photodiode. That is, as the amount of received light increases, the voltage due to the photovoltaic power increases logarithmically. Therefore, when the LED 2 is used as a light receiving element, the voltage (V) generated in the second amplifying resistance element 11 has a proportional relationship with a value obtained by logarithmically compressing the amount of light received by the LED 2. Hereinafter, a connection point between the second amplification resistance element 11 and the drain of the MOSFET 9 is referred to as a point A.
[0048]
Therefore, the voltage (V) generated in the second amplification resistance element 11 is a BV value (brightness value: Cd / m) obtained by logarithmically compressing the reflection brightness value of the subject.²) Can be suitably used as the measured value. The BV value is used as a value indicating the luminance of an object such as a subject. When the brightness is reduced by half, the BV value increases by one.
[0049]
FIG. 2 shows a case where the voltage at point A is associated with the BV value based on the relationship between the voltage (V) generated in the second amplification resistance element 11 shown in FIG. FIG. 9 is a luminance characteristic diagram showing one example. In this luminance characteristic diagram, the BV value on the horizontal axis is on the logarithmic axis. In the characteristic line of FIG. 2, when the brightness is reduced by half and the voltage generated in the second amplification resistance element 11 is reduced by about 0.25 V, the BV value is increased by one.
[0050]
Further, as shown in the characteristic diagram of FIG. 2, when the voltage (V) generated in the second amplifying resistance element 11 shown in FIG. 1 is used as the BV value, the detection dynamic range of the BV value becomes 2^-1From 2¹²Up to 2¹³A very wide dynamic range can be secured. Therefore, the voltage at the point A can be suitably used as a detected value of luminance under any photographing environment from a dark room to outdoors.
[0051]
In the auto strobe device according to the first embodiment, a third amplification resistance element 12 as a parallel resistance element is connected to the plus terminal of power storage member 1 so as to be in parallel with second amplification resistance element 11. A DC cut capacitor 13 is connected between the third amplification resistance element 12 and point A. The third amplification resistance element 12 and the DC cut capacitor 13 are connected in series with each other, and are entirely connected in parallel with the second amplification resistance element 11. Hereinafter, a connection point between the third amplification resistance element 12 and the DC cut capacitor 13 is referred to as a point B. The voltage at the point B is a voltage obtained by logarithmically compressing the change in luminance.
[0052]
FIG. 3 shows a time change of the voltage at the point A (the voltage generated in the second amplification resistance element 11) and the voltage at the point B (the third amplification resistance element) when the strobe circuit 14, which will be described later, emits full light. 12 is a characteristic diagram showing a time change with respect to (voltage generated at 12). In this way, by connecting the third amplification resistance element 12 in parallel with the second amplification resistance element 11 together with the DC cut capacitor 13, the voltage at the point A (the second amplification resistance From the voltage generated at the element 11, a voltage at the point B (a voltage based on only an AC change in the amount of received light), which is a voltage that does not vary depending on the external light luminance from which the DC component has been removed, can be obtained.
[0053]
The third amplification resistance element 12 is connected to the base terminal of the integrating PNP transistor 15 that operates as an integrating transistor. The emitter terminal of integrating PNP transistor 15 is connected to the positive terminal of power storage member 1 via integrating resistance element 16. The collector terminal of the integrating PNP transistor 15 is connected to the integrating capacitor 17. The other end of the integrating capacitor 17 is connected to the frame ground 3.
[0054]
The integration PNP transistor 15 is turned on when a voltage is generated in the third amplification resistance element 12. The integrating capacitor 17 is charged by a current flowing from the emitter terminal to the collector terminal of the integrating PNP transistor 15 in the ON state.
[0055]
The voltage at the point B is a voltage obtained by logarithmically compressing a change in the amount of light received by the LED 2. The relation between the base voltage of the integrating PNP transistor 15 and the collector current is an exponential function. Therefore, the collector current of the integrating PNP transistor 15 is proportional to the amount of change in the amount of light received by the LED 2. Therefore, for example, if the amount of light received by the LED 2 doubles, the collector current of the integrating PNP transistor 15 also doubles.
[0056]
As a result, for example, an amount of charge proportional to the area of the hatched region S in FIG. 3 is stored in the integrating capacitor 17. That is, the charge that is proportional to the value obtained by integrating the change in the amount of light received by the LED 2 is accumulated in the integrating capacitor 17. The integration capacitor 17 generates a voltage proportional to a value obtained by integrating a change in the amount of received light received by the LED 2.
[0057]
Therefore, the voltage of the integrating capacitor 17 can be used as a value indicating the total light amount of the changing light received by the LED 2. That is, the voltage of the integrating capacitor 17 can be used as a detection value of the total value of the reflected light amount of the strobe light from the strobe circuit 14 to be described later.
[0058]
Note that a discharging resistor 18 is connected in parallel to the integrating capacitor 17. The charge stored in the integrating capacitor 17 is discharged according to the time constant of the integrating capacitor 17 and the discharge resistance element 18. The strobe light is long at about 2 ms even at full lighting. The time until the shutter of the camera is fully opened is usually about 5 ms. Therefore, for example, when the charging voltage of the integrating capacitor 17 is used as a measured value of the total amount of reflected light of the strobe light by the subject, the capacitance value of the integrating capacitor 17 and the resistance value of the discharge resistance element 18 are used. The determined time constant may be set to about 100 ms. Thus, the voltage of the integrating capacitor 17 can be used as a sufficiently accurate detection value during the light emission control period.
[0059]
As described above, in the first embodiment, the voltage generated in the LED 2 by the photoelectromotive force is amplified by the MOSFET 9, and the collector current of the integrating PNP transistor 15 is controlled by a voltage obtained by cutting a DC component from the amplified voltage. The integration capacitor 17 is being charged. Therefore, the voltage generated in the integrating capacitor 17 has the following characteristics.
[0060]
First, light is received by the LED 2 having the same structure as a photodiode having a response speed about 1000 times faster than that of the phototransistor, and the integration capacitor 17 is charged based on the change. Therefore, for example, a phototransistor is used in place of the integrating PNP transistor 15, and the voltage of the voltage generated in the integrating capacitor 17 is smaller than when the integrating capacitor 17 is charged based on a change in light received by the phototransistor. The ability to follow the change in the amount of light emitted from the strobe light is improved.
[0061]
As a result, for example, a voltage that follows the change in the amount of reflected light of the strobe light by the subject can be generated in the integrating capacitor 17. The amount of strobe light reflected by the subject increases and changes sharply as the maximum output light amount of the strobe light increases. In the case of a camera incorporating the strobe circuit of the first embodiment, even when the strobe circuit 14 is combined with a high-output strobe circuit 14, the total sum of the amounts of strobe light reflected by the subject can be accurately integrated. It can be detected as the voltage of the capacitor 17.
[0062]
Further, even when the flash light is being emitted, the voltage of the integrating capacitor 17 becomes more accurately proportional to the total value of the reflected light amount of the flash light by the subject up to that time. Therefore, for example, during the emission of the strobe light, the total value of the reflected light amount of the strobe light by the subject up to that time is detected, and when the total value of the reflected light amount becomes a desired value or more, the emission of the strobe light is stopped. In such exposure control, the amount of strobe light reflected by the subject can be accurately controlled.
[0063]
Second, after the signal is once amplified by the MOSFET 9, the DC component is cut from the amplified voltage, and the integration capacitor 17 is charged again via the integration PNP transistor 15. Accordingly, even if the voltage generated in the second voltage-dividing resistance element 5 becomes a bias voltage and the MOSFET 9 is always in the ON state, or the periphery of the LED 2 is bright, the voltage canceled as a DC component is obtained. Is generated in the integrating capacitor 17.
[0064]
Therefore, the charging voltage of the integrating capacitor 17 is directly proportional to the amount of light received by the LED 2, even though the LED 2 is biased by the second voltage-dividing resistance element 5. Even if the area around the LED 2 is bright, the charging voltage of the integrating capacitor 17 is directly proportional to the amount of light received by the LED 2.
[0065]
As a result, even if a bias voltage is applied to the LED 2, the total value of the amount of strobe light reflected by the subject can be detected as the charging voltage value of the integrating capacitor 17. Further, even in a case where the strobe light is caused to emit a synchro light during the daytime and the light other than the strobe light is incident on the LED 2, the total value of the reflected light amount of the strobe light by the subject is calculated as: It can be detected as a charging voltage value of the integrating capacitor 17. Based on the charging voltage of the integrating capacitor 17, it is possible to accurately control the total value of the strobe light reflected by the subject, and thus the total exposure of the CCD and the silver halide film.
[0066]
In the first embodiment, the charging voltage of the integrating capacitor 17 is used for controlling the amount of light emitted from the strobe circuit 14.
[0067]
The strobe circuit 14 includes a xenon discharge tube 20 serving as a discharge tube that emits strobe light when a voltage of several kV is applied, and an IGBT (cathode) connected between the cathode terminal of the xenon discharge tube 20 and the frame ground 3. Insulated Gate Bipolar Transistor 21, a main capacitor 22 connected in parallel with the entire xenon discharge tube 20 and the IGBT 21, a booster circuit 23 connected to the power storage member 1 and outputting a voltage of several hundred volts, and a trigger circuit 24 And A protection resistance element 25 is connected between the gate terminal of the IGBT 21 and the frame ground 3.
[0068]
The voltage output from the booster circuit 23 is supplied to the main capacitor 22. A rectifier diode 26 that allows a current to flow from the booster circuit 23 to the main capacitor 22 is provided between the booster circuit 23 and the main capacitor 22. Note that the voltage output from the booster circuit 23 is about 300V.
[0069]
The trigger circuit 24 includes a trigger transformer 27 having a secondary winding connected to the trigger terminal of the xenon discharge tube 20, a trigger capacitor 28 connected in series with the primary winding of the trigger transformer 27, a primary winding and a trigger capacitor. And a thyristor 29 forming a current closed loop together with the, and a trigger charging resistor element 30 connected between the anode terminal of the thyristor 29 and the high voltage side terminal of the booster circuit 23. A protection resistance element 31 and a protection capacitor 32 are connected in parallel between the gate terminal of the thyristor 29 and the frame ground 3. One end of each of the primary winding and the secondary winding of the trigger transformer 27 is connected to the frame ground 3.
[0070]
In such a strobe circuit 14, the main capacitor 22 is charged with the voltage output from the booster circuit 23. The trigger capacitor 28 is charged with a current flowing through the trigger charging resistor 30 and the primary winding of the trigger transformer 27. The final charging voltage of the trigger capacitor 28 is equal to the charging voltage of the main capacitor 22.
[0071]
When the gate terminal of the thyristor 29 is controlled to a high level while the trigger capacitor 28 is charged, the thyristor 29 is turned on. The electric charge charged in the trigger capacitor 28 flows in a current closed loop formed by the thyristor 29 and the primary winding of the trigger transformer 27, and a voltage is generated in the primary winding. A voltage is generated in the primary winding, and a voltage is also generated in the secondary winding. At the voltage of the secondary winding, emission of strobe light from the xenon discharge tube 20 is started. At this time, when the IGBT 21 is on, the xenon discharge tube 20 continues to emit strobe light by the voltage of the main capacitor 22. The strobe light becomes weaker as the voltage of the main capacitor 22 decreases. When the voltage of the main capacitor 22 falls below a predetermined voltage, the xenon discharge tube 20 turns off.
[0072]
Note that, even if the gate voltage of the IGBT 21 is lowered to control the IGBT 21 to be turned off before the xenon discharge tube 20 is turned off, the xenon discharge tube 20 is turned off. That is, when the gate terminal of the thyristor 29 is controlled to a high level and then the gate terminal of the IGBT 21 is controlled to a low level, the xenon discharge tube 20 emits strobe light during a period between these controls. Become.
[0073]
Further, the amount of strobe light emitted from the xenon discharge tube 20 becomes almost the same every time if the charging voltage of the main capacitor 22 immediately before the light emission is the same every time. Therefore, if the period from when the gate terminal of the thyristor 29 is controlled to the high level to when the gate terminal of the IGBT 21 is controlled to the low level is shortened, the total amount of light emitted from the xenon discharge tube 20 can be reduced. Conversely, if the period is lengthened, the total amount of light emitted from the xenon discharge tube 20 can be increased. Note that, even during this period, even if the voltage of the main capacitor 22 becomes longer than the predetermined voltage, the xenon discharge tube 20 is turned off due to the voltage drop of the main capacitor 22. Does not increase. The period until the xenon discharge tube 20 is turned off due to the voltage drop of the main capacitor 22 is called a full light emission period.
[0074]
Further, in the first embodiment, a control circuit is provided in order to control the amount of light emitted from the flash circuit 14 and the like.
[0075]
The control circuit includes a comparator 41 in which the charging voltage of the integrating capacitor 17 is connected to an inverting input terminal, a reference voltage circuit 42 that outputs a reference voltage to a non-inverting input terminal of the comparator 41, and control means that outputs a control signal. And a microcomputer 43. This microcomputer 43 also controls the overall operation of the camera.
[0076]
The output terminal of the comparator 41 is connected to the gate terminal of the IGBT 21. Further, a pull-up resistance element 44 is connected between the output terminal of the comparator 41 and the plus terminal of the power storage member 1. Therefore, when no voltage is output from the comparator 41, a high level is input to the gate terminal of the IGBT 21, and the IGBT 21 is maintained in the ON state.
[0077]
The reference voltage circuit 42 includes a reference voltage PNP transistor 51 having an emitter terminal connected to the plus terminal of the power storage member 1, a reference voltage capacitor 52 connected to the frame ground 3, and a collector terminal of the reference voltage PNP transistor 51. A reference voltage charging resistance element 53 connected between the reference voltage capacitor 52 and the other end of the reference voltage capacitor 52; and a reference voltage discharge resistance element 54 connected in parallel with the reference voltage capacitor 52.
[0078]
A third control resistance element 55 is connected between the emitter terminal and the base terminal of the reference voltage PNP transistor 51, and one end of a fourth control resistance element 56 is connected to the base terminal. . The other end of the fourth control resistance element 56 is connected to the microcomputer 43 as described later.
[0079]
Therefore, for example, when the other end of the fourth control resistance element 56 is set to the same level as the frame ground 3, a voltage is generated in the third control resistance element 55 and the fourth control resistance element 56, and the reference voltage PNP The transistor 51 is turned on. The reference voltage capacitor 52 is charged by the current flowing from the emitter terminal to the collector terminal of the reference voltage PNP transistor 51 in the ON state. The charging voltage of the reference voltage capacitor 52 increases in accordance with a time constant determined by the capacitance value of the reference voltage capacitor 52 and the resistance value of the reference voltage charging resistance element 53.
[0080]
Conversely, for example, when the other end of the fourth control resistance element 56 is at the same level as the positive terminal of the power storage member 1, no voltage is generated in the third control resistance element 55 and the fourth control resistance element 56. Therefore, the reference voltage PNP transistor 51 is turned off. The electric charge stored in the reference voltage capacitor 52 is discharged via the reference voltage discharge resistance element 54. When the discharge is completed, the voltage of the reference voltage capacitor 52 becomes 0V.
[0081]
Therefore, for example, by controlling the duty ratio of the on-period to the total on-off time of the reference voltage PNP transistor 51 in a range of 0 to 100%, the charging voltage of the reference voltage capacitor 52 is reduced to the voltage of the minus terminal of the power storage member 1. Can be set to an arbitrary voltage between the voltage of the positive terminal and the voltage of the plus terminal.
[0082]
When the charge voltage of the reference voltage capacitor 52 is kept constant for a relatively long period, the shorter the cycle of the on / off control of the reference voltage PNP transistor 51, the shorter the charge / discharge charge of the reference voltage capacitor 52. The amount can be reduced, and the charging voltage of the reference voltage capacitor 52 can be accurately stabilized at a desired voltage.
[0083]
The microcomputer 43 is connected to the point A and the reference voltage capacitor 52. The microcomputer 43 is connected to the base terminal of the switching PNP transistor 6 via the second control resistance element 8 and to the base terminal of the reference voltage PNP transistor 51 via the fourth control resistance element 56. And is connected to the gate terminal of the thyristor 29. Further, an imaging button 61, a mode setting switch 62, a shutter driving mechanism 63, and the like are connected to the microcomputer 43.
[0084]
Next, the operation of the entire camera based on the control of the microcomputer 43 will be described. FIG. 4 is a flowchart illustrating a control flow of the microcomputer 43.
[0085]
In the following description, the imaging button 61 is a two-stage button having a half-pressed state in which it is slightly pressed down and a full-pressed state in which it is completely pressed down. The half pressed state corresponds to the first stage of exposure, and the full pressed state corresponds to the second stage of exposure.
[0086]
When the power switch of the camera (not shown) is turned on, the power of the power storage member 1 is supplied to the entire circuit of the camera including the microcomputer 43. Further, the booster circuit 23 outputs a predetermined high voltage. As a result, the main capacitor 22 and the trigger capacitor 28 are charged. The IGBT 21 is turned on by the pull-up resistance element 44.
[0087]
When activated, the microcomputer 43 performs an initial setting process (step ST1). In this initial setting process, the microcomputer 43 controls the gate terminal of the switching PNP transistor 6 and the gate terminal of the reference voltage PNP transistor 51 to high level. These transistors 6 and 51 are both turned off. Thereby, the LED 2 is turned off. Further, the reference voltage capacitor 52 is not charged, and the voltage input from the reference voltage capacitor 52 to the microcomputer 43 is also the voltage of the frame ground 3. In the initial setting process, the gate terminal of the thyristor 29 is controlled to a low level. Thus, the thyristor 29 is turned off.
[0088]
On the other hand, the MOSFET 9 is turned on by the two voltage dividing resistance elements 4 and 5. Therefore, when external light is incident on the LED 2 in the off state and a photovoltaic power is generated in the LED 2, the voltage obtained by amplifying the photovoltaic power changes the voltage at point A. The voltage at the point A is input to the microcomputer 43.
[0089]
When the initialization is completed, the microcomputer 43 enters a state of waiting for a half-press operation of the imaging button 61 (step ST2).
[0090]
When the imaging button 61 is slightly pressed, the microcomputer 43 reads the settings of the mode setting switch 62 and the like, and determines the shooting mode based on the settings of the mode setting switch 62 and the like (step ST3). The shooting mode determined here includes, for example, a manual shooting mode and an automatic shooting mode.
[0091]
The microcomputer 43 subsequently performs an internal setting process according to each shooting mode (step ST4).
[0092]
For example, in the automatic photographing mode, the microcomputer 43 reads the voltage at the point A and determines the BV value based on the luminance characteristic diagram of FIG. The BV value at this time is a brightness value of the brightness around the camera. That is, the LED 2 is used for photometry. The relationship line between the voltage at point A and the BV value shown in the luminance characteristic diagram of FIG. 2 may be stored in a storage member (not shown) in the microcomputer 43 as a relational expression or a lookup table. Good.
[0093]
The microcomputer 43 determines an optimal combination of the aperture and the shutter speed based on the determined BV value, and sets the determined aperture and shutter speed. At this time, for example, if there is a detailed mode setting such as an aperture priority mode or a shutter priority mode, a combination of the aperture according to the priority and the shutter speed is determined.
[0094]
Further, particularly when there is a fine mode setting such as the aperture priority mode or the shutter priority mode, if the optimal combination of the aperture and the shutter speed cannot be obtained, the microcomputer 43 sets the predetermined aperture to the predetermined aperture. The shutter speed is selected, and the amount of light insufficient for the combination is calculated.
[0095]
The microcomputer 43 calculates the amount of strobe light reflected by the subject that can compensate for the insufficient amount of light, and calculates the charging voltage of the integrating capacitor 17 based on the amount of reflected light, that is, the charging voltage held in the reference voltage capacitor 52. Is calculated. Then, the microcomputer 43 sets the gate terminal of the reference voltage PNP transistor 51 to low level, turns on the transistor 51, and controls the reference voltage PNP transistor 51 so as to have the calculated charging voltage.
[0096]
When the reference voltage PNP transistor 51 is turned on, the reference voltage capacitor 52 is charged through the reference voltage charging resistance element 53. The voltage of the reference voltage capacitor 52 rises toward the power storage member 1 by a time constant determined by the reference voltage resistance element 53 and the reference voltage capacitor 52. On the other hand, the voltage of the reference voltage capacitor 52 is converted into a digital signal by the A / D conversion input terminal R1 of the microcomputer 43, and is compared with the already calculated voltage to be held in the reference voltage capacitor 52.
[0097]
When the voltage of the reference voltage capacitor 52 matches the calculated value, the microcomputer 43 sets the base terminal of the reference voltage PNP transistor 51 to high level, and turns off the reference voltage PNP transistor 51. As a result, charging of the reference voltage capacitor 52 is stopped, so that the reference voltage is maintained.
[0098]
Further, the microcomputer 43 sets the flash flag provided in the microcomputer 43 as “valid”. The strobe flag includes "valid" and "invalid". "Valid" means that strobe light is emitted at the time of imaging, and "invalid" means that strobe light is not emitted at the time of imaging. I do.
[0099]
Note that the calculated charging voltage (reference voltage) is stored in the storage member of the microcomputer 43, and the control for charging the reference voltage capacitor 52 to a desired charging voltage after the imaging button 61 is fully pressed. May be executed.
[0100]
Further, when the self-timer is set in the auto shooting mode, the microcomputer 43 sets the self-timer flag provided in the microcomputer 43 to “valid”. The self-timer flag includes “valid” and “invalid”. “Valid” means that self-timer imaging is performed, and “invalid” means that self-timer imaging is not performed.
[0101]
When the above series of settings is completed, the microcomputer 43 enters a state of waiting for a full press operation of the imaging button 61 (step ST5). However, when the half-press operation state is released without the full-press operation of the imaging button 61 (step ST6), the microcomputer 43 returns to the state of waiting for the half-press operation of the imaging button 61 in step ST2 again. .
[0102]
When the imaging button 61 is pressed to the end, the microcomputer 43 first reads a self-timer flag (step ST7).
[0103]
When the self-timer flag is set to "invalid", the microcomputer 43 immediately outputs an image pickup signal (step ST8). The exposure operation of the camera is started by the output of the imaging signal. Specifically, the imaging signal is output to the shutter driving mechanism 63. The shutter driving mechanism 63 opens the shutter at the timing when the imaging signal is input, and closes the shutter when a preset shutter opening period elapses. When the strobe flag is set to “valid”, the microcomputer 43 controls the gate terminal of the thyristor 29 to a high level in synchronization with the opening of the shutter. That is, the strobe light is emitted when the shutter is opened.
[0104]
When the gate terminal of the thyristor 29 is controlled to a high level, a voltage is generated in the secondary winding of the trigger transformer 27 by the electric charge stored in the trigger capacitor 28. In addition, since the IGBT 21 is in the ON state, strobe light is emitted from the xenon discharge tube 20. The strobe light is reflected by a subject of the camera or the like, and received by a silver halide film or a CCD (not shown) via a shutter.
[0105]
The strobe light is reflected by a subject or the like, and a part thereof returns to the camera. The strobe light reflected by the subject or the like also enters the LED 2. The LED 2 generates a photoelectromotive force according to the amount of incident light. The voltage generated in the LED 2 by the photovoltaic power is amplified by the MOSFET 9 and changes the voltage at the point A as shown in FIG. The higher the voltage generated in the LED 2 by the photovoltaic power, the lower the potential at the point A. Further, as shown in FIG. 3, when the electric potential at the point A changes by the strobe light, the electric potential at the point B changes accordingly. When the potential at point B drops, the integrating PNP transistor 15 is turned on, and the integrating capacitor 17 is charged.
[0106]
When the charging voltage of the integrating capacitor 17 becomes higher than the charging voltage of the reference voltage capacitor 52, the comparator 41 drives its output terminal to a low level (frame ground 3). When a low level is input to the gate terminal of the IGBT 21, the IGBT 21 is turned off. When the IGBT 21 is turned off, the xenon discharge tube 20 is turned off, and the emission of the strobe light ends.
[0107]
In this way, the reference voltage capacitor 52 is charged in advance to a voltage corresponding to the desired total received light amount, and the reference voltage capacitor 52 and the charging voltage of the integration capacitor 17 are compared to charge the strobe light. The total sum of the amounts of light reflected by the subject can be set to a predetermined value. At this time, the LED 2 is used for controlling strobe light.
[0108]
When the imaging is completed, the microcomputer 43 returns to step ST2 and returns to the state of waiting for the half-press operation of the imaging button 61 again. The microcomputer 43 controls the shutter driving mechanism 63 together with the control of the strobe light, and causes the shutter to close when a predetermined time has elapsed.
[0109]
If the self-timer flag read when the imaging button 61 is operated is “valid” (Yes in step ST7), the microcomputer 43 performs switching for a predetermined time, for example, 10 seconds. The PNP transistor 6 is turned on and off. When the switching PNP transistor 6 is turned on, the LED 2 is turned on. When the switching PNP transistor 6 is turned off, the LED 2 is turned off. By repeating the lighting and the turning off, the LED 2 blinks (step ST9). That is, at this time, the LED 2 is used as a waiting time display of the self-timer.
[0110]
When the switching PNP transistor 6 is switched between the ON state and the OFF state, the switching cycle and the duty ratio of the ON period may be constant, but, for example, the blinking speed of the LED 2 gradually increases. As described above, the switching cycle may be gradually shortened, or the duty ratio of the ON period may be changed.
[0111]
When a preset period elapses, the microcomputer 43 keeps the switching PNP transistor 6 in an off state and outputs an imaging signal (step ST8). The shutter driving mechanism 63 opens the shutter at the timing when the imaging signal is input, and closes the shutter when a preset shutter opening period elapses. When the strobe flag is “valid”, the microcomputer 43 controls the gate terminal of the thyristor 29 to a high level. Thereafter, the microcomputer 43 returns to step ST2, and returns to the state of waiting for the half-pressing operation of the imaging button 61 again.
[0112]
In step ST2, when the imaging button 61 is half-pressed and it is determined in step ST3 that the mode is the manual shooting mode, the microcomputer 43 reads the aperture and shutter speed settings, and reads these settings. The aperture is set to operate with the value, and the shutter speed is set in the shutter drive mechanism.
[0113]
Further, when the total value of the reflected light amount of the strobe light by the subject is set in the manual photographing mode, the microcomputer 43 calculates the charging voltage of the integrating capacitor 17 at the total value of the reflected light amount, and refers to it. The reference voltage PNP transistor 51 is turned on so that the detected value of the charging voltage of the voltage capacitor 52 becomes the calculated voltage. Further, the microcomputer 43 sets a strobe flag provided in the microcomputer 43 to “valid”.
[0114]
Further, when the self-timer is set in the manual shooting mode, the microcomputer 43 sets the self-timer flag provided in the microcomputer 43 to "valid" in step ST4.
[0115]
The operation of the entire camera (step ST5 to step ST9) after the imaging button 61 is fully pressed is the same as in the automatic imaging mode, and a description thereof will be omitted.
[0116]
FIG. 5 shows a time characteristic diagram of the charging voltage of the integrating capacitor 17. This time characteristic diagram is a time characteristic diagram of a charging voltage measured in a state where a virtual illumination lamp that emits a constant amount of light is turned on alongside a camera. In a state where the voltage at the point A is directly input to the base terminal of the integrating PNP transistor 15, this corresponds to a time characteristic diagram of the measured charging voltage.
[0117]
As shown in FIG. 5, when the distance between the camera and the subject is 1 m, the charging voltage of the integrating capacitor 17 is charged in proportion to the passage of time according to the first charging characteristic line 71. When the distance between the camera and the subject is 2 m, the charging voltage of the integrating capacitor 17 is charged in proportion to the passage of time according to the second charging characteristic line 72. The inclination of the second charging characteristic line 72 is １ ／ of the inclination of the first charging characteristic line 71.
[0118]
In FIG. 5, the first reference voltage Vref1 is a reference voltage when the sensitivity of the film is ISO (International Organization For Standardization) 100. The second reference voltage Vref2 is a reference voltage when the film sensitivity is ISO200. The second reference voltage Vref2 is half the voltage of the first reference voltage Vref1.
[0119]
Therefore, if the strobe light is assumed to have the same light emission characteristics as a virtual illumination lamp that emits a certain amount of light, and if an image of an object having a darkness at a distance of 2 m is picked up using an ISO100 film, refer to The first reference voltage Vref1 may be set in the voltage capacitor 52, and the IGBT 21 may be turned off after a lapse of t2 from the start of the flash emission. In addition, when an image of a subject with a low brightness at a distance of 1 m is captured using a film of ISO 100, the first reference voltage Vref1 is set in the reference voltage capacitor 52, and t1 (= t2 / 4) from the start of strobe light emission. ) After the lapse of time, the IGBT 21 may be turned off. The time until the IGBT 21 is turned off is the quench time. This quenching time is usually the time from the start of the flash emission to the turning off of the IGBT 21. However, if the shutter opening is delayed after the flash emission, the time from the start of the shutter opening to the turning off of the IGBT 21. It becomes.
[0120]
The relationship between the subject distance and the quench time can also be explained as follows.
[0121]
In a case where an image of an object having a low object brightness is captured at a distance of 2 m using an ISO100 film and the aperture value of the camera is fixed at F4, the guide number value GNo is set to 8 (= 2 × 4). Become. The quench time under the setting of the camera and the imaging condition under which the light emission stop signal is generated when the guide number GNo is 8 is t2. Also, a reference voltage that allows proper exposure in such a setting is defined as a first reference voltage Vref1.
[0122]
In general, when the same subject is imaged at two types of imaging distances, the logarithmic ratio between these reflected light amounts is obtained by replacing the guide number value GNo with a light emission guide number value GV represented by the following equation 1. It can be considered as a difference between the guide number values (hereinafter, referred to as a GV difference (ΔGV)). Further, in the first embodiment, since the charging voltage of the integrating capacitor 17 for integrating the reflected light amount is proportional to time, the logarithmic ratio of time can also be considered as a GV difference (ΔGV).
[0123]
GV = {(logGNo / log2) × 2} Expression 1
[0124]
Therefore, the GV difference (ΔGV) has the relationship of the following equation 2. However, in Equation 2, t 'is the quench time for the longer distance to the subject, and t is the quench time for the shorter distance to the subject. In the camera with the above setting, when the distance to the subject is 1 m, the guide number GNo is 4, and the GV is (log4 / log2) × 2 = 4. On the other hand, when the subject distance is 2 m, since the guide number GNo is 8, the GV is (log8 / log2) × 2 = 6.
[0125]
ΔGV = {log (t ′ / t) / log2} Equation 2
[0126]
Therefore, the quench time t1 for obtaining an appropriate exposure when an image of a subject at a distance of 1 m is captured by the camera having the above-described setting can be calculated by the following Expression 3, and is a quarter of the time when the distance is 2 m.
[0127]
GNo (1m) = 1 × 4 = 4
GV (1m) = log4 / log2 × 2 = 4
ΔGV = 6-4 = 2
log (t2 / t1) / log2 = ΔGV = 2
t2 / t1 = {10^0.602= 4
{T1} = {t2 / 4}...
[0128]
Also, as shown in FIG. 5, when the charging voltage of the integrating capacitor 17 and the time are in a proportional relationship, the logarithmic ratio between the charging voltages when the same subject is imaged at two different film sensitivities. Can be considered as a GV difference (ΔGV). That is, Equation 4 below is obtained. Here, Vref 'is the higher charging voltage and Vref is the lower charging voltage. The general formula of the guide number GNo of the strobe light is the following formula 5. Here, F is the aperture value, D is the subject distance (unit is m), and the film sensitivity is a numerical value represented by ISO.
[0129]
ΔGV = {log (Vref ′ / Vref) / log2} Equation 4
GNo = {F × D} (film sensitivity / 100)^1/2・ ・ ・ Equation 5
[0130]
Therefore, in the camera having the above-described setting, for example, when the subject distance is 2 m and the film sensitivity changes from ISO 100 to ISO 200, the reference voltage can be calculated by the following formula group 6. That is, when the film sensitivity is changed from ISO 100 to ISO 200, the reference voltage is halved. When changing from ISO 200 to ISO 400, the reference voltage becomes １ ／ of the reference voltage of ISO 200. That is, as shown in FIG. 5, the second reference voltage Vrer2 is half of the first reference voltage Vref1.
[0131]

[0132]
Next, a description will be given of a method of setting a reference voltage in the case of so-called mixed light, which is a case in which strobe light is used in a situation where external light luminance exists in the camera having the above-described configuration.
[0133]
The exposure amount of the camera is EV (Electron @ Volto) under the condition of only external light brightness without using strobe light. Assuming that the external light luminance exposure amount is, for example, 80%, the insufficient exposure amount ΔEV is calculated by the following equation 7, and becomes −0.32.
[0134]
ΔEV = {log 0.8 / log 2 = −0.32} Equation 7
[0135]
In the case where the insufficient 20% exposure is compensated for by the strobe light, ΔGV is calculated by the following Expression 8, and becomes −2.32.
[0136]
ΔGV = {log 0.2 / log 2 = −2.32} Equation 8
[0137]
Since ΔGV = −2.32, the reference voltage can be calculated by the following equation group 9 including equation 4. Here, since ΔGV is minus, Vref ′ and Vref in Expression 4 are reversed. Assuming that the reference voltage only for the external light luminance is Vref 'and the reference voltage when using strobe light is Vref, Vref is 20% of Vref'. Therefore, if the reference voltage when using only the external light luminance is 1 V, 0.2 V is used as the reference voltage of the 20% strobe light.
[0138]
log (Vref / Vref ') / log2 = ΔGV = −2.32
Vref / Vref '= 10^-0.698= 0.2
{Vref} = {0.2Vref ”} Equation 9
[0139]
When the contribution ratio of the strobe light to the amount of exposure is X, the reference voltage can be obtained by the following Expression 10 as a general expression. However, Vref1 at which the strobe light gives 100% exposure is 1V.
[0140]
X = 1-10^{ΔEV × log2}
ΔGV = {log (X) ÷ log2
Vref = 10^{log2 × ΔGV}・ ・ ・ Formula 10
[0141]
As described above, in the camera according to the first embodiment, by blinking the LED 2, it is possible to display a waiting state after operating the imaging button 61 during imaging using the self-timer. Further, a BV value having a very wide dynamic range can be detected based on the amount of light received by the LED 2. That is, photometry of external light becomes possible. Further, the reflected light of the strobe light is received by the LED 2, and photometry of only the strobe light is enabled. Further, the total value of the reflected light amount of the strobe light by the subject can be controlled based on the total value of the received light amount of the LED 2. Further, by enabling the photometry of the external light and the photometry of only the strobe light, it is possible to perform high-precision control in all the strobe use areas including the mixed light area.
[0142]
In particular, since the DC cut capacitor 13 is provided between the MOSFET 9 and the integrating PNP transistor 15, the integrating PNP transistor 15 charges the integrating capacitor 17 based only on the change of the photovoltaic power of the LED 2. It becomes. Therefore, even when the surrounding environment is bright, the strobe light can be emitted so as to appropriately compensate for the insufficient light amount of the subject. Further, since the LED 2 is used as the light receiving element for receiving the strobe light, the charging voltage of the integrating capacitor 17 follows the total light emission amount of the actual strobe light better than when the phototransistor is used as the light receiving element. I do. As a result, the insufficient light amount can be more accurately compensated than when the phototransistor is used as a light receiving element.
[0143]
In addition, since one LED 2 is used to detect an exposure amount for exposure calculation and a total amount of strobe light reflected by the subject, these are combined with a phototransistor and a CdS light receiving cell as in the related art. It is not necessary to consider a light-receiving characteristic error between light-receiving elements as in the case of detecting by detecting. As a result, it is possible to more accurately control the total exposure amount of so-called mixed light, for example, to emit strobe light in a situation where the periphery of the LED 2 is bright.
[0144]
As described above, in the camera according to the first embodiment, the surrounding light amount in the automatic imaging mode is detected using the LED 2 as the light emitting element, and the total value of the strobe light reflected by the subject is detected. be able to. Therefore, in a conventional camera, for example, a light emitting element for a self-timer, a CdS light receiving cell for detecting the amount of ambient light, and a phototransistor for detecting the amount of strobe light are separately used. One LED 2 can be shared. It should be noted that the above three functions are not fulfilled by one LED 2, but the two functions of photometry of the subject and detection of the reflected light amount of the strobe light are shared by the LED 2, and another light emitting element for the self-timer is added. Alternatively, two or more of the three functions may be shared by the LED 2.
[0145]
As a result, the number of sensors provided in the camera is reduced, and effects such as reduction in size and weight of the camera, improvement in design freedom, and reduction in failure rate can be obtained. In addition, even a low-priced camera can realize a high-performance camera with a small number of parts. In particular, since the aperture and shutter speed of the camera are set using the BV value detected by the LED 2, it is possible to suppress an increase in cost as a whole.
[0146]
In the camera according to the first embodiment, the LED 2, which is originally a light emitting element, is also used as a light receiving element. As a result, the light emitting direction and the light emitting range of the LED 2 become the light amount detecting direction and the light amount detecting range as they are. When a CdS light receiving cell for detecting the amount of ambient light or a phototransistor for detecting the amount of strobe light is used in a camera, the light amount detecting direction and the light amount detecting range must be designed for each light receiving element. In addition, a large number of prototypes of cameras having different layouts must be created for each light receiving element, and the light receiving direction and the light receiving range of each prototype must be measured one by one. However, according to the first embodiment, it is possible to easily measure the light receiving angle and the light receiving range simply by turning on the LED 2 and measuring the irradiation angle and the irradiation range. As a result, the light receiving angle of the LED 2 as the light receiving element and the light receiving lens (not shown) on the front surface of the LED 2 can be easily corrected, so that the design period of the camera is greatly shortened, and the cost of the prototype is reduced.
[0147]
Further, according to the first embodiment, if information on the aperture value (F-number) to be used can be obtained, it can be used whether the exposure control method of the camera is a program shutter or an aperture priority shutter. Become. Further, the present invention is not limited to the mechanical shutter, and can be applied to a camera using an electronic shutter such as a CCD.
[0148]
The above embodiment is a preferred embodiment of the present invention, but is not limited thereto, and various modifications and changes can be made without departing from the gist of the present invention. For example, a photodiode may be used instead of LED2.
[0149]
In the first embodiment, the strobe light is emitted simultaneously with the opening of the shutter, and when the total value of the amount of reflected light of the strobe light by the subject reaches a predetermined total value of the light amount, the shutter is closed. In addition, for example, when the distance to the subject is measured in advance based on the AF function or the like, the total amount of the strobe light reflected by the subject up to the reference time is determined based on the shutter closing timing. The strobe light may be emitted by a predetermined time earlier than the closing time of the shutter so that the value becomes the desired sum of the light amounts. This makes it possible to similarly control the total value of the amount of strobe light reflected by the subject while the shutter is open.
[0150]
In the first embodiment, the voltage at the point A is input to the microcomputer 43 as it is. In addition, for example, a capacitor may be provided between the point A and the microcomputer 43. This makes it possible to accurately detect the average BV value of the subject even under a situation where the strobe light of another camera is shining.
[0151]
In the first embodiment, the reference voltage is generated by charging the reference voltage capacitor 52. In addition to this, for example, a resistor element group corresponding to the sensitivity of the silver halide film or CCD and a resistor element group corresponding to the aperture value are provided, and control is performed to select an appropriate combination of the resistor elements from among them. , A reference voltage may be generated.
[0152]
However, when the reference voltage is generated by combining the resistance elements as in this modification, the number of the resistance elements to be used increases. Therefore, Embodiment 1 has a simpler configuration. In addition, compared to this modification, the first embodiment can set an arbitrary voltage with high accuracy and fineness. In controlling the mixed light or the like, the first embodiment can take advantage of the good follow-up property of the LED 2. Thus, it is possible to control the amount of light accurately. Furthermore, in the first embodiment, since the total value of the amount of reflected strobe light by the subject can be controlled to one step or less of the BV value, imaging is performed with a CCD having a low light receiving sensitivity latitude (narrow dynamic range). Even in the case of performing the above, it is possible to capture a high-quality image by appropriately correcting the amount of light.
[0153]
【The invention's effect】
In the present invention, since a photodiode or an LED is used as a light receiving element, the range of measurable luminance is wider than when a phototransistor is used as a light receiving element. In addition, the circuit configuration can be simplified, and the arrangement space for the light receiving elements can be reduced. Further, in the present invention, since a photodiode or LED is used as a light receiving element, the light receiving element can follow the rising edge of a high-power strobe light whose light quantity increases or decreases rapidly, and a phototransistor is used as the light receiving element. Responsiveness is improved as compared with.
[Brief description of the drawings]
FIG. 1 is a circuit diagram of a camera incorporating an auto strobe circuit according to Embodiment 1 of the present invention.
FIG. 2 associates a voltage at a point A with a BV value based on a relationship between a voltage (V) generated in a second amplification resistance element in FIG. 1 and a light receiving amount of an LED serving as a light receiving element. FIG. 7 is a luminance characteristic diagram showing an example of the case where the image is displayed.
FIG. 3 shows a time change of a voltage at a point A (a voltage generated in a second amplifying resistance element) and a voltage of a point B (a third amplifying resistance element) when the strobe circuit in FIG. FIG. 6 is a characteristic diagram showing a temporal change with respect to a voltage generated in FIG.
FIG. 4 is a flowchart illustrating a control flow of the microcomputer in FIG. 1;
FIG. 5 is a time characteristic diagram of a charging voltage of the integrating capacitor in FIG. 1;
[Explanation of symbols]
2 LED (light receiving element)
5 Second voltage divider resistor (bias resistor)
6 switching PNP transistor (switching transistor)
9 MOS type field effect transistor (MOSFET, amplification transistor)
11 Second amplifying resistor (amplifying resistor)
12 Third amplification resistance element (parallel resistance element)
13 DC cut capacitor
15 integration PNP transistor (integration transistor)
17 ° integration capacitor
20 Xenon discharge tube (discharge tube)
41 ° comparator
42 ° reference voltage circuit
43 microcomputer
51 PNP transistor for reference voltage (transistor for reference voltage)
52 capacitor for reference voltage

Claims (7)

In an auto strobe device that outputs strobe light by emitting light from a discharge tube,
A light-receiving element comprising a photodiode or an LED for receiving the reflected light of the strobe light from a subject or the like
A bias resistance element for applying a bias voltage to a cathode electrode of the light receiving element;
An amplification transistor in which an anode electrode of the light receiving element is connected to a gate terminal;
An amplification resistor connected to a drain terminal of the amplification transistor;
An integration transistor in which the collector current increases as the voltage of the amplification resistance element increases;
An integrating capacitor charged by the collector current,
A reference voltage circuit that outputs a reference voltage;
A comparator for comparing the charging voltage of the integration capacitor with the reference voltage,
When the comparator determines that the charging voltage of the integrating capacitor is higher than the reference voltage, the automatic strobe device turns off the discharge tube. A parallel resistance element, comprising a DC cut capacitor connected in series with the parallel resistance element,
The parallel resistance element and the DC cut capacitor are entirely connected in parallel with the amplification resistance element,
2. The auto strobe device according to claim 1, wherein a connection point between the parallel resistance element and the DC cut capacitor is connected to a base terminal of the integration transistor. 2. The auto strobe device according to claim 1, further comprising a control unit that detects a voltage generated in the amplification resistance element and sets a reference voltage calculated based on the detected voltage as a BV value in the reference voltage circuit. . The reference voltage circuit,
A reference voltage capacitor;
A reference voltage transistor having a collector terminal connected to the reference voltage capacitor,
Control means for detecting a voltage at a connection point between the amplifying resistance element and the DC cut capacitor, and setting a reference voltage calculated as a BV value of the detected voltage in the reference voltage circuit is provided. Item 6. An auto strobe device according to Item 1. Using an LED as the light receiving element,
A switching transistor having a collector terminal connected to the anode electrode of the LED;
2. The auto strobe device according to claim 1, further comprising control means for controlling on / off of the switching transistor. In an auto strobe device that outputs strobe light by emitting light from a discharge tube,
It has a light receiving element composed of a photodiode or an LED for receiving the strobe light reflected by a subject or the like. An auto strobe device characterized by the above-mentioned. A camera comprising the auto strobe device according to claim 1.

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