JPH08242407A - Automatic aperture controller for lens for television camera - Google Patents

Abstract

PURPOSE: To obtain exposure well balanced as a whole even in the presence of an object having high luminance by limiting an output level of an amplifier circuit controlling an aperture based on an image signal to be a desired value. CONSTITUTION: An image signal from a television camera is given to a terminal 1, and the signal is outputted to an output terminal 13 as an inverted amplification signal Vac via an inverting input terminal 11 of an operational amplifier A1. The inverted amplification signal Vac drives a drive coil 6 of a servo meter M via an operational amplifier A2 and Darlington transistors (TR2 , TR3 ). When an object is bright, the servo meter M drives the aperture in its closing direction and the gain for the case is set by a variable resistor VR1. A limiter circuit comprising a diode D2 and a variable resistor VR2 is provided in parallel with the variable resistor VR1 to limit an amplitude of the inverted amplification signal Vac due to the presence of the object having high luminance. Collapse of parts of the image other than the high luminance part due to excess aperture closing of the high luminance part of the image is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic diaphragm control device for a television camera lens.

[0002]

2. Description of the Related Art Conventionally, as a device for automatically controlling the aperture of a television camera lens, a one-sided spring drive system has been known, but it has a narrow drive voltage range and is unreliable. As described in Japanese Laid-Open Patent Publication No. 59-108455, the one in which the diaphragm is controlled to open and close in both directions has been highly prized for its high reliability and low current consumption.

However, recently, a small size of a television camera lens is particularly desired. Therefore, in the conventional bidirectional drive system, the circuit structure is large because the drive current is supplied in both directions of opening and closing the diaphragm. There was a complicated and troublesome problem. In the case of a TV camera lens, when a high-brightness signal is included in a part of the image signal, such as when imaging a subject with high contrast, the narrowing-down adjustment is performed based on that part of the high-brightness signal. Get lost. If such a narrowing adjustment is performed, most of the low-luminance subjects will be underexposed, and the quality of the image will be deteriorated as a whole.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and is a lens for a television camera capable of a well-balanced exposure as a whole even if a high-luminance object is partially included. It is an object of the present invention to provide an automatic diaphragm control device of the above.

[0005]

SUMMARY OF THE INVENTION The present invention that achieves the above object is an automatic aperture control device for a television camera lens, which controls the aperture of the television camera lens based on an image signal from the television camera. It is characterized by including an amplifier circuit for amplifying an input image signal and a limiter circuit with a variable limit value for limiting the output level of the amplifier circuit.

[0006]

EXAMPLES The present invention will be described in detail with reference to the examples shown below. In FIG. 1, reference numeral 1 is an input terminal for inputting an image signal Vin from a television camera, which is connected to an inverting amplification voltage doubler rectifier circuit I. In the inverting amplification rectifier circuit I, the input terminal 1 is connected to the ground terminal 4 via the resistor R2, and is also connected to the inverting input terminal 11 of the operational amplifier A1 via the capacitor C2 and the resistor R3. The non-inverting input terminal 12 of the operational amplifier A1 is a midpoint voltage terminal 2 which will be described later.
And a variable resistor VR as a feedback resistor between the inverting input terminal 11 and the output terminal 13.
1 is provided.

The inverting amplification voltage doubler rectifier circuit I has a configuration in which the capacitor C2 inversely amplifies the image signal Vin from which the direct current component has been removed, and the inverted amplification signal Vac is obtained at the output terminal 13, but the variable resistor VR1 is adjusted. By doing so, the gain (amplification factor) of the operational amplifier A1 can be continuously changed. That is, when the resistance value of the variable resistor VR1 is increased, the gain increases, and conversely, when the resistance value is decreased, the gain decreases. Therefore, in FIG. 2, for example, the optimum image signal level of the camera is high and the input image signal Vin is high. In this case, the input change amount γ becomes large, but in such a case, the resistance value is adjusted to be small so that the gain becomes small. Conversely, when the input change amount γ of the image signal Vin is small, the resistance value is increased. Then, the gain is adjusted so as to be large so that the inverted amplified signal Vac having a constant output can always be obtained. In this case, since the size of the input image signal Vin has a width corresponding to the overall brightness of the subject, the main purpose is to adjust the image output signal when the subject has a low contrast.

Reference numeral II is a limiter circuit for continuously limiting the output on the negative side (the image signal output corresponding to the bright portion of the entire screen) of the image signal inverted and amplified by the operational amplification A1. The limiter circuit II is provided in parallel with the variable resistor VR1 and comprises a diode D2 and a variable resistor VR2 for controlling a current flowing through the diode D2, and connects the inverting input terminal 11 of the operational amplifier A1 and the anode of the diode D2. In addition, the cathode and the output terminal 13 are connected via the variable resistor VR2.

This limiter circuit II has a solid line (2) in FIG.
As shown in FIG. 7, the negative side of the output voltage of the operational amplifier A1 is forcibly suppressed by the diode D1 to obtain the input / output characteristic. That is, in FIG. 3, the horizontal axis is configured so that when the input voltage V11 at the inverting input terminal 11 of the operational amplifier A1 is higher than the level α, the output voltage V13 has a limiter characteristic of being constant at the level β. There is. The vertical axis shows the output voltage V13 of the output terminal 13, and the broken line (1) shows the original characteristics when the limiter is not applied. In this way, the limiter circuit II limits the peak of the bright image signal so that the output voltage V13 does not exceed the level β, so that it is possible to prevent the aperture from being narrowed down too much when the subject has a high contrast.

The inverted signal Vac obtained by the inverting amplification voltage doubler rectifier circuit I is rectified by the voltage doubler rectifier circuit. The voltage doubler rectifier circuit connects a voltage doubler capacitor C3 to the output terminal 13, connects the output terminal 14 of the capacitor C3 and the midpoint voltage terminal (line) 2 via a diode D3, and outputs the inverted signal Vac. A doubled voltage signal V14 obtained by adding the negative side inversion level to the positive side level is obtained, and the output terminal 14 is further provided.
A diode D4 is connected in the forward direction to obtain a rectified signal Vdc. Capacitor C4 and resistor R5
Are provided between each of them and the ground terminal 4 in order to smooth the rectified signal Vdc.

The rectified signal Vdc is connected to the inverting input terminal 21 of the operational amplifier A2 in order to obtain the control signal of the servo meter for driving the automatic diaphragm through the resistor R6. A resistor R7 is provided between the inverting input terminal 21 and the output terminal 23 of the operational amplifier A2 as a feedback resistor that determines the amplification factor in relation to the resistor R6. C5 is an integrating capacitor provided in parallel with the resistor R7. In addition, the inverting input terminal 21
Is connected to the output end of the operation detecting coil 5 of the diaphragm control servometer M via a resistor R9 so that a feedback signal for braking the servometer M can be obtained. The other output end of the detection coil 5 is connected to the midpoint voltage terminal 2. Further, the non-inverting input terminal 22 of the operational amplifier A2 is connected to the midpoint voltage terminal 2 via the resistor R8. Therefore, the operational amplifier A2 receives the rectified signal Vdc.
And the midpoint voltage V0 which is based on the braking signal of the detection coil 5
When the signal at the inverting input terminal 21 is large, the difference from the midpoint voltage V0 of the non-inverting input terminal 22 is small, the control signal at the output terminal 23 is small, and conversely the signal at the inverting input terminal 21 is When it is small, the difference from the midpoint voltage of the non-inverting input terminal 22 becomes large, and a large control signal Vout can be obtained at the output terminal 23.

The control signal Vout is supplied to a one-way drive circuit having a voltage gain so that the servometer M for controlling the aperture is driven by a greatly increased drive voltage. That is, the output terminal 23 of the operational amplifier A2
Is connected to the ground terminal 4 via a resistor R10, and is also connected to the base of the transistor TR2 via a resistor R11. The collector of the transistor TR2 is
It is connected to the positive terminal 3 of the power source through a resistor R12 and is also connected to the base of a pair of transistors TR3. The emitter of the transistor TR2 is connected to the ground terminal 4 via the resistor R14, while the transistor T2 is connected to the transistor T2.
It is connected to the collector of R3 via a feedback resistor R13.
The emitter of the transistor TR3 is connected to the positive terminal 3 of the power source. Reference numeral 6 denotes a drive coil of the one-way drive circuit of the servo meter M, which is connected to the collector side of the transistor TR3 and one terminal, and the other terminal is connected to the ground terminal 4 of the power supply circuit. The transistors TR2 and TR3 are in Darlington connection, and are configured to supply a voltage having a very large amplification factor to the drive coil 6 in proportion to the control signal Vout applied to the base of the transistor TR2.

In the illustrated embodiment, the diaphragm driving servometer M always applies a rotational force to the diaphragm closing direction by a spring 7, and the driving coil 6 resists the spring 7 to actuate the servometer M. It is configured to drive in the aperture opening direction and perform aperture control in balance with the spring 7.

Reference numeral III is a power supply voltage stabilizing circuit for stabilizing the power supply voltage for keeping the power supply voltage constant. This power supply voltage stabilizing circuit III connects the input terminal 8 of the power supply to the collector of the transistor TR1 and also connects the series resistor R1.
And via the capacitor C1 to the ground terminal 4,
A transistor TR is provided between the resistor R1 and the capacitor C1.
1 is connected to the base and is also connected to the ground terminal 4 via the Zener diode D1.
By keeping the voltage of the base constant regardless of the voltage change of the input terminal 8, a constant voltage and current are supplied to the plus terminal 3 of the power supply which is the emitter terminal of the transistor TR1.

Reference numeral V is a midpoint voltage supply circuit connected to the power source voltage stabilizing circuit III, and outputs the intermediate (preferably 1/2) voltage of the stabilized power source voltage to the midpoint voltage terminal 2. It is configured as follows. In the case of this embodiment, a smoothing capacitor C7 is provided between the positive terminal 3 and the ground terminal 4.
And series resistors R15 and R16 having the same resistance value are provided in parallel, and a contact 51 between the resistors R15 and R16 is connected to the midpoint voltage terminal 2 to provide half the power supply voltage to the midpoint voltage terminal 2. It is provided to output the voltage of. C6 is the midpoint voltage terminal 2
Is a smoothing capacitor connected between the ground terminal 4 and the ground terminal 4.

The operation mode of the embodiment having the above-mentioned structure will be described. It is assumed that the image signal Vin from the television camera enters the input terminal 1 with a waveform as shown in FIG. 4B corresponding to the test chart of FIG. This waveform is
The rectangular part on the plus side corresponds to the bright part of the image, and Vd
Indicates the image level, Vs indicates the synchronization level, and Vp-p indicates the amplitude. The DC component of the image signal Vin is removed by the capacitor C2, and as shown in FIG. 5, the image signal Vin is balanced so that the areas on the plus side and the minus side are equal with respect to the reference voltage V0. This signal is inverted and amplified by the operational amplifier A1 with the midpoint voltage V0 supplied from the midpoint voltage terminal 2 as a reference, as shown in FIG. 6 (a), and becomes the inverted signal Vac at the output terminal 13. Since the gain (amplification factor) of the operational amplifier A1 is determined by the ratio of the resistance value of the variable resistor VR1 to the resistance R3, the magnitude of the gain can be adjusted by adjusting the resistance value of the variable resistor VR1. The amplitude can be scaled.
Therefore, the sensitivity adjusting means is suitable for adjusting the image signal at the time of low contrast.

Next, in the limiter circuit II, by adjusting the variable resistor VR2, the portion corresponding to the bright portion of the image signal is limited, and the dark portion can be adjusted as the main subject at the time of high contrast. First, when the variable resistance VR2 is adjusted to make the resistance value infinite, the limiter circuit II does not operate and the inverted signal Vac has a waveform similar to that shown in FIG. When this inverted signal Vac is input to the capacitor C3 of the voltage doubler rectifier circuit, the diode D3 is turned on by the signal on the minus side to charge the capacitor C3, and the signal on the plus side is added subsequently, and the voltage doubler signal is shown in FIG. 7 (b). As shown in Fig. 4, DC rectification is performed with the amplitude unchanged.
A control signal suitable for setting the bright portion for detecting the image level Vd in (b) as the main subject is obtained.

Next, when the resistance value of the variable resistor VR2 is set to 0, the diode D2 becomes conductive, the bright portion of the image signal Vin is cut as shown by (2) in FIG. Vac, and when this inverted signal is rectified by the voltage doubler signal, it is DC-reproduced as shown in FIG. 7B as in the previous case. So in this case,
It is possible to obtain a control signal suitable for setting the cut dark portion of the bright portion of the image signal Vin as the main subject. Also,
In this case, at the time of low contrast when the amplitude of the bright portion of the image signal Vin is small, even if the limiter acts, the influence thereof is small. Therefore, even if this means is adjusted, the image output signal set by the sensitivity adjusting means described above is obtained. Don't make a big difference.

The rectified signal Vdc is input to the inverting input terminal 21 of the operational amplifier A2, compared with the midpoint voltage of the non-inverting input terminal 22 and the midpoint voltage of the terminal 2 by the operational amplifier A2, and controlled at the output terminal 23. The signal Vout is obtained. At this time, since the feedback signal of the detection coil 5 of the servo meter M is also input to the inverting input terminal 21, the control signal Vout also includes the braking signal of the servo meter M.

The control signal Vout has two transistors T
The unidirectional drive circuit having a large voltage gain of Darlington connection composed of R2 and TR3 can be inputted, and a very large drive voltage can be supplied to the drive coil 6 of the servometer M by a small control signal. That is, the transistor T
The voltage from the positive terminal 3 is greatly amplified and supplied to the collector side of the transistor TR3 in proportion to the change of the control signal Vout applied to the base of R2. For example, the drive coil 6 opens the diaphragm by a predetermined amount with respect to the servo meter M which is always biased by the spring 7 with a predetermined spring elasticity in the closing direction by the control signal Vout when the optimum image signal is applied to the predetermined subject. If the state of the subject does not change while the angle is kept, the control signal Vout does not change, and the voltage supplied from the power supply of the drive coil 6 is also held. If the condition of the subject changes and becomes brighter, for example, the rectified signal Vdc
Becomes higher, the voltage at the output terminal 23 (control signal Vout) becomes smaller as compared with the midpoint voltage in the operational amplifier A2, the base voltage of the transistor TR2 of the one-way drive circuit decreases, and the collector current of the transistor TR2 decreases. , The base voltage of the transistor TR3 decreases due to the voltage drop across the resistor R12, the collector current of the transistor TR3 decreases, the current flowing through the drive coil 6 decreases, and the voltage decreases.
The diaphragm is driven in the closing direction by the spring 7 to maintain the next optimum image signal state.

On the contrary, when the subject becomes dark, the rectified signal Vdc becomes low, the output signal (control signal Vout) of the operational amplifier A2 becomes large, and the base voltage of the transistor TR2 of the one-way drive circuit rises. Transistor TR
The collector current of 2 increases, the base voltage of the transistor TR3 increases due to the voltage increase due to the resistor R12, the collector current of the transistor TR3 increases, the current flowing through the drive coil 6 increases, and the voltage increases, and the servometer M causes the spring 7 to move. The lens is driven in the direction of opening the aperture against, and the next optimum image signal state is maintained.

In the power supply voltage stabilizing circuit III, the base voltage of the transistor TR1 is kept constant by the resistor R1, the capacitor C1 and the Zener diode D1 so that the collector side is supplied from the input terminal 8 of the power supply. The voltage is constantly supplied to the plus terminal 3 on the emitter side, the midpoint voltage of the inverting amplification voltage doubler rectifier circuit I and the limiter circuit II is kept constant, and the power supply voltage of the diaphragm control circuit IV is kept constant, so that It is increasing the nature.

Further, the midpoint voltage supply circuit V supplies the midpoint voltage of the stabilized power source voltage to the operational amplifiers A1 and A2 of the circuit so that the midpoint voltage can be obtained by one power source. It is possible to obtain the control signal Vout based on the above and at the same time amplify this to drive the diaphragm control servometer.

[0024]

As described above, the present invention provides a limiter circuit for limiting the output level of an amplifier circuit for amplifying an image signal within a certain range in an automatic diaphragm apparatus for controlling an aperture based on an image signal from a television camera. Since it is provided, even if there is a peak in a part of the image signal when a high-contrast subject is imaged, the aperture is not excessively narrowed down, and it is possible to obtain a high-quality image signal as a whole.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment of the device of the present invention.

FIG. 2 is an explanatory view explaining an operation of the inverting amplifier circuit of the device of the present invention.

FIG. 3 is an explanatory diagram showing an operation of a limiter circuit II of the device of the present invention.

FIG. 4 is an explanatory diagram showing a relationship between a subject and an image signal.

FIG. 5 is a schematic explanatory diagram of an input waveform before control by the means of the present invention.

FIG. 6 is a schematic explanatory diagram illustrating a control waveform by means of the present invention.

FIG. 7 is a schematic explanatory diagram illustrating a control waveform by means of the present invention.

[Explanation of symbols]

 1 Image signal input terminal 2 Midpoint voltage terminal 3 Positive terminal 4 Ground terminal 5 Detection coil 6 Driving coil 7 Spring 8 Power input terminal I Inversion amplification voltage doubler rectifier circuit II Limiter circuit III Power supply voltage stabilization circuit IV Aperture control circuit V Mid-point voltage supply circuit A1 operational amplifier A2 operational amplifier M Servo meter for diaphragm drive

Claims (4)

[Claims] 1. An automatic aperture control device for a television camera lens, which controls an aperture of a lens for a television camera based on an image signal from the television camera, and an amplifier circuit for amplifying an image signal input from the television camera. An automatic aperture control device for a lens for a television camera, comprising: a limiter circuit having a variable limit value for limiting an output level of the amplifier circuit. 2. The amplifier circuit according to claim 1, wherein the amplifier circuit includes an operational amplifier circuit that inverts and amplifies the image signal in a variable amplification factor with respect to a reference voltage, and the limiter circuit includes an output of the operational amplifier circuit. A voltage doubler rectifier including a diode and a variable resistance means connected between the image signal input and an inverting input terminal, and further doubling the voltage of the image signal inverted and amplified by the operational amplifier circuit to convert it into a direct current. An automatic iris control device for a lens for a television camera, comprising a circuit. 3. The variable resistance means according to claim 2, wherein a variable resistance means is connected in parallel with the diode and the variable resistance means between the output terminal and the inverting input terminal of the operational amplifier circuit. Automatic aperture control device for TV camera lens. 4. The automatic aperture control device for a lens for a television camera according to claim 1, wherein the limiter circuit limits a peak level of an image signal input to the amplifier circuit.