JPH0132027Y2 - - Google Patents

Description

[Detailed description of the invention] The present invention provides an electric shutter in which a reference voltage for exposure control and a reference voltage for luminance verification are derived from one voltage setting section, and the luminance-resistance characteristic of a photoconductive element is The present invention relates to an exposure control/brightness verification circuit capable of compensating for increased deviations in the reference voltage for brightness verification when compensation for variations in the voltage setting section (in a low brightness region) is performed by adjusting the voltage setting section.

First, while explaining the configuration of the present invention with reference to FIG. 1, the purpose of the present invention will be described.

R ₁ is a photoconductive element such as CdS, R ₂ is a comparison resistor for low luminance verification, C is a capacitor for light intensity integration,
CP ₁ is a comparator circuit for exposure control, CP ₂ is a comparator circuit for low luminance verification, OP is an operational amplifier circuit for inversion amplification, and R ₃ is a reference voltage for exposure control and a reference voltage for luminance verification. is a potentiometer that can set and compensate for variations in the low brightness region in the brightness-resistance characteristics of the photoconductive element _R1 , _R4 is an input resistor, _R5 is a feedback resistor, _T1 and _T2 are The transistors I ₁ and I ₂ are inverter circuits, SW is a switch for switching between brightness verification mode and exposure control mode and for starting exposure control, T ₀ is an exposure control output, and L ₀ is a brightness verification output.

The present invention connects a comparison resistor R ₂ , a photoconductive element R ₁ and a capacitor C in series in that order, and connects a non-element element (capacitor C and comparison resistor R ₂ ) to a semiconductor switch ( transistors T ₂ and T ₁ ), and independent comparator circuits (CP ₂ CP ₁ ).
A brightness verification circuit and an exposure control circuit are constructed by using two of the following.

Note that by connecting a comparison resistor, a photoconductive element, and a capacitor in series in the order of photoconductive element, capacitor (comparison resistor), and comparison resistor (capacitor), the non-element element can be controlled by a semiconductor switch in the brightness verification mode and exposure control mode. There is a method in which the brightness verification _circuit and the exposure control circuit are constructed by shooting according to There are some disadvantages in its operation.

In the configuration of the present invention, when the reference voltage for exposure control and the reference voltage for brightness verification are obtained in common by one potentiometer _R3 , simply as the reference voltage of the comparator circuit _CP2 , The intermediate tap terminal of potentiometer _R3 can be connected to the inverting input terminal (-). That is, basically, based on a certain standard brightness-resistance characteristic of the photoconductive element _R1 , for example, the comparator circuit _CP1
The reference voltage applied to the inverting input terminal (-) of
2 (K=0.5), and under that condition, the capacitance value of the capacitor C is selected so that a predetermined time can be obtained. On the other hand, the comparison resistor R ₂ has a low resistance under the conditions of the standard brightness-resistance characteristic of the photoconductive element R ₁ and the reference voltage (Vcc/2) applied to the inverting input terminal (-) of the comparator circuit CP ₂ . A resistance value is set as a brightness test level. Here K=
The reason for setting it to 0.5 is that the area near the center of the power supply voltage is most frequently used, and it is of course possible to select another value.

If there are no variations in the characteristics of the photoconductive elements used individually, there is no problem with the above conditions, but
Since there are variations in the characteristics of photoconductive elements, it is necessary to compensate for them.

In other words, when the capacitance value of the capacitor is selected based on the standard characteristics of the photoconductive element, if there are variations in the characteristics of the photoconductive element in the low brightness region, adjust the potentiometer _R3 . to compensate for the variation.

For example, in the case of variations in the sensitization tendency, potentiometer R ₃ is adjusted so that its partial pressure constant K is greater than 0.5.

This compensates for errors in the exposure time due to variations in the characteristics of the photoconductive elements.

However, under the above conditions the comparative resistance R ₂
In a brightness verification circuit in which the resistance of the photoconductive element is set to a constant value, if there are variations in the sensitization tendency in the characteristics of the low brightness region of the photoconductive element, the inverting input terminal (-) of the comparator circuit _CP2 is The applied reference voltage must be adjusted so that the voltage division constant K is less than 0.5.

That is, the comparator circuit CP ₁ for exposure control
A reference voltage for the comparator circuit _CP2 for luminance verification is simply provided by a common potentiometer _R3 , and the low luminance region in the luminance-resistance characteristic of the photoconductive element is adjusted by adjusting the potentiometer _R3 . If the variation in is compensated for, the reference voltage of one circuit will be adjusted in a direction that increases the variation.

As mentioned above, an object of the present invention is to provide a reference voltage for a first comparator circuit for exposure control and a second comparator circuit for brightness verification using a common potentiometer. The divided voltage by the potentiometer is given as the reference voltage of the first comparator circuit, and the set center value of the reference voltage of the first comparator circuit is given as the reference voltage of the second comparator circuit for luminance verification. Even if the exposure control circuit compensates for variations in the characteristics of the photoconductive element by adjusting the potentiometer, the luminance verification circuit will still maintain the allowable range without adjustment. The present invention provides an exposure control/brightness verification circuit for an electric shutter that is capable of absorbing errors in the brightness of the shutter.

Hereinafter, an embodiment of the present invention will be described based on FIG.

First, the relationship among exposure time t, capacitor C, and photoconductive element (resistance) R ₁ is as follows: Vc = V ₁ = Vcc (1-e ^-1/CR1 ) t = CRln (1/1-K) However, V ₁ = KVcc.

Here, it is assumed that the value of the capacitor C is set so that the specified time can be obtained around K=0.5.

Next, the voltage relationship at each point when the photoconductive element _R1 varies is determined.

The reference voltage V ₁ of the comparator circuit CP ₁ is V ₁ =Vcc (1-e ^{- t0/CR10} ) where R ₁₀ is the center value of R ₁ and t ₀ is the specified time in seconds corresponding to R ₁₀ .

Next, the output voltage of the operational amplifier circuit OP, that is, the reference voltage V ₂ of the comparator circuit CP ₂ is as follows: V ₂ = Vcc/2 + G (V ₁ - Vcc/2) = Vcc/2 (1 - G) + GVcc (1 -e ^-t0/CR10 ) 1+G(1-2A)/2Vcc However, G= _-R5 / _R4 , e ^t0/CR10 =A.

Also, the brightness comparison voltage V ₃ of the comparator circuit CP ₂
is V ₃ =R ₁₀ /R ₁₀ +R ₂ Vcc.

Therefore, if we find the relationship between G and comparative resistance R ₂ such that when R is ₁₀ , it will reach the specified test standard level, then from V ₂ = V ₃ , 1 + G (1 - 2 A) / 2 = R ₁₀ / R ₁₀ + R ₂ R ₂ =1-G(1-2A)/1+G(1-2A) _R10 .

When the value of the comparison resistor R ₂ is constant and R ₁₀ deviates due to variations in the characteristics of the photoconductive element, finding the condition for G that makes the verification standard level V ₂ = V ₃ is as follows: R ₁ = αR ₁₀ (However, α varies) From equations (1) and (2), Expanding the above equation on the left side, we get becomes.

And when A=0.5, G is It is expressed as

If the converted value G is calculated by substituting numerical values for A and α, the result will be as shown in FIG. Note that α is assumed to be 2 ^-1 to ²¹ times as the range of variation in the photoconductive element R ₁₀ .

In other words, by setting G to 0.723, which corresponds to α = 2 ⁰ (between 2 ^-1/3 and 2 ^1/3 ), G will be fixed even if α varies in the range of 2 ^-1 to ^{2 1/3} . The correction error of the reference voltage of the comparator circuit CP ₂ due to this is a slight difference, and the error of the brightness verification is within the maximum of about 2 ^±0.1 when converted to the resistance value error of the photoconductive element R ₁ , and γ = 0.5. When converted to Ev, it falls within the range of +0.2Ev to -0.2Ev. This is sufficiently permissible compared to ±1Ev, which is the normal standard for cameras.

Note that the reference voltage of the operational amplifier circuit OP is fixed and set to 1/2 (Vcc/2) of the power supply voltage. This Vcc/2 has no absolute meaning, but if it is set to 1/2 of the power supply voltage, the reference voltage for exposure control will not necessarily be set to Vcc/2, but It has a wide range of flexibility.
On the other hand, when A≠0.5, α
Although it is possible to calculate G corresponding to , there is no positive reason to set it in this way, so the explanation will be omitted.

In addition, correction of variations in the high brightness region in the brightness-resistance characteristics of the photoconductive element _R1 is usually performed using the photoconductive element R1.
This is done by connecting a semi-fixed resistor in series to _R1 , but this is omitted to simplify the explanation.

As described above, exposure control and brightness verification in an electric shutter in which the comparison resistor, photoconductive element, and capacitor are connected in series in that order, and the reference voltage for the exposure control circuit and the brightness verification circuit is commonly provided by one potentiometer. In the circuit, the reference voltage of the luminance verification circuit is given by a predetermined negative multiplying factor of the difference from the set center value of the power supply voltage.
Even if the variation in the brightness-resistance characteristic of the photoconductive element relative to the exposure control circuit is compensated for by adjusting the potentiometer, the effect of the adjustment on the brightness verification circuit is absorbed within the tolerance.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is a chart of calculated numerical values of the conversion value G. R ₁ ... Photoconductive element, R ₂ ... Comparison resistance, C ...
Capacitor, T ₁ , T ₂ ... Transistor, R ₃ ...
Potentiometer, CP ₁ , OP ₂ ... Comparator circuit, OP ... Operational amplifier circuit, R ₄ ... Input resistance,
_R5 ...Feedback resistance.

Claims (1)

[Scope of utility model registration request] The comparison resistor R ₂ for luminance verification, the photoelectric element R ₁ and the capacitor C are connected in series in that order, and the comparison resistor R 2 is connected in series in that order.
A first semiconductor switch (transistor T ₁ ) is connected in parallel with _R2 , which is cut off in the brightness test mode and made conductive in the exposure control mode, and connected in parallel with the capacitor C, which is made conductive in the brightness test mode and cut off in the exposure control mode. The reference voltage of the first comparator circuit CP ₁ that compares the integrated potential at the connection point of the photoconductive element R ₁ and the capacitor C is connected to the second semiconductor switch (transistor T ₂ ) that is connected to the photoconductive element R ₁ . A potentiometer _R3 divides _the adjustable power supply voltage Vcc to compensate for variations in the low brightness range in the brightness-resistance characteristics of The difference from the reference voltage Vcc/2 when no adjustment is required by inputting it to OP is applied to the output of the inverting amplifier circuit OP with a negative multiplier determined by the ratio of the input resistance _R4 of the inverting amplifier circuit OP to the feedback resistor _R5 . the inverting amplifier circuit as a reference voltage for the second comparator circuit CP ₂ which converts into a voltage and compares the voltage at the connection point of the comparison resistor R ₂ and the photoconductive element R ₁
Exposure control and brightness verification in an electric shutter, characterized in that the error in brightness verification due to variations in the brightness-resistance characteristics of the photoconductive element _R1 is within ±1 Ev by applying the output voltage of the OP. circuit.