JPH038527B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an aperture adjustment device for an imaging means suitable for use in television cameras and the like.

Generally, the relationship between the rotation angle θ of a diaphragm blade, which adjusts the size of the diaphragm aperture in a camera, and the amount L of incident light passing through the aperture has nonlinearity, as shown by the solid line A in FIG. 4. Therefore, when adjusting the aperture value using an electric circuit, a part of the control system is provided with a circuit having the opposite characteristic as shown by the dotted line B in Fig. 4, and the correction is performed in a linear manner as shown in Fig. 4 C. It is necessary to obtain certain characteristics.

The present invention is intended to solve the above problems,
An embodiment in which the present invention is applied to a television camera having an automatic aperture adjustment device will be described below with reference to the drawings.

Conventionally, automatic aperture adjustment devices installed in television cameras automatically adjust the aperture by detecting the level of the video signal output from the image pickup tube and controlling the aperture adjustment motor according to this detection level. I'm trying to adjust it. During this automatic adjustment, for example, if the same subject is to be imaged for a long time, the aperture value at that time may be locked and held. In preparation for such a case, the automatic diaphragm adjustment device is provided with a lock device.

FIG. 1 shows a first embodiment in which the present invention is applied to a circuit including the automatic aperture adjustment device and lock device.

In FIG. 1, an aperture 2 provided on an image pickup tube 1
The aperture value is adjusted by rotating the aperture blades by an aperture adjustment motor 3 and adjusting the size of the aperture 4. At the same time, the slider 11 of the variable resistor 10 is configured to slide in conjunction with the aperture 2. When performing automatic aperture adjustment, switch 5 is opened and switch 6 is closed. The output video signal from the image pickup tube 1 is sent to a subsequent signal processing circuit through a preamplifier 7, and its signal level is detected by a detection circuit 8 comprising a diode _D1 and a capacitor _C1 .
The time constant of this detection circuit 8 is selected so that semi-peak detection, which detects an intermediate level between peak detection and average value detection, is performed. The detection voltage of the detection circuit 8 is applied to the voltage comparator circuit 9 and the reference voltage V _S
compared to This comparison voltage controls the motor 3 through the diode _D2 , so that the aperture value of the aperture 2 is controlled to be constant according to the signal level.
At this time, the voltage from the slider 11 of the variable resistor 10 is
Aperture value voltage V _I1 is obtained by dividing V _CC at a level corresponding to the aperture value, and this voltage V _I1 is
is added to the negative terminal of

On the other hand, for example, an 8-bit counter 13 counts the clock _Pck applied to the input terminal 14,
It is reset at predetermined intervals by a reset signal S _R applied to the input terminal 15. Note that the clock _Pck is synchronized with the horizontal scanning of the beam of the image pickup tube 1, for example.
It has a frequency of 15.75KHz and also has a reset signal S _R
has a frequency of, for example, 60 Hz that is synchronized with vertical scanning. Further, the operation of this counter 13 is stopped by the output of the voltage comparator circuit 12. The count value of the counter 13 is latched by the latch circuit 17 through the switch 6 at a timing based on the output of the voltage comparison circuit 12. This latched count value is converted into a voltage V _I2 by a ladder circuit 18 consisting of a resistor network and applied to the positive terminal of the voltage comparison circuit 12. The voltage comparison circuit 12 stops the counting operation of the counter 13 when V _I1 and V _I2 become equal, and causes the latch circuit 17 to take in the count value at that time. Therefore, the count value changes as shown in FIG. 2 and is reset for each field.

Next, when locking the aperture value in the automatic aperture adjustment state, apply the lock instruction signal S _C to the input terminal 16 at a desired time, for example at the time of "LOCK" in FIG. 2, close the switch 5, and 6 is opened, and further the operation of the voltage comparison circuit 9 is stopped. As a result, the automatic adjustment loop is released, and the value of V _I2 at that time is locked as shown in FIG. 2, and this V _I2 and V _I1 at that time are compared in the voltage comparison circuit 12. This comparison voltage controls the motor 3 through the diode D ₃ and the switch 5, thereby forming a position control loop with the locked V _I2 as the target value. As a result, the aperture value at the time of locking is locked constant.

FIG. 3 shows a second embodiment.

In this embodiment, an up-down counter is used as the counter 13, and its counting direction is determined by the output of the voltage comparison circuit 12. Also, the switch 6 and latch circuit 17 in FIG. 1 are omitted, and the count value of the counter 13 is determined by the ladder circuit 18
It is converted into a voltage V _I2 and applied to the voltage comparator circuit 12.

In the above configuration, the switch 5 is opened during automatic aperture adjustment, and the voltage comparator circuit 9 performs the same operation as in the case of FIG. During this time, the counter 13 counts up using the output of the voltage comparison circuit 12 when V _I2 <V _I1 , and counts down using the output when V _I2 > V _I1 .

In order to perform locking in this state, a signal S _C is applied to the input terminal 16 to close the switch 5 and stop the operation of the voltage comparator circuit 9.
stop the operation. As a result, a position control system is formed in which the voltage comparison circuit 12 always controls the aperture value so that _VI1 and _VI2 are equal, and the aperture value is locked. This lock can be held for a long time if V _I2 is held.

In each of the embodiments shown in FIGS. 1 and 3, the manual aperture adjustment can be performed with the operation of the voltage comparator circuit 9 stopped and the switch 5 closed. In that case, while operating with the clock added by the counter 13 in the above state,
The aperture value can be adjusted by manually selecting the counting direction, changing V _I2 , and controlling the motor 3.

Next, a case will be described in which the characteristics of the aperture and the amount of incident light are corrected using the ladder circuit 18.

The ladder circuit 18 is composed of a resistor network, and if the above correction is not performed, in FIG. 3, for example, as shown in FIG. A resistor connected to seven resistors each having a resistance value of R as shown in the figure is used. In addition, in the case of the embodiment shown in Fig. 1,
The ladder circuit 18 is connected to the fifth output terminal of the latch circuit 17.
Connect as shown. In the present invention, by selecting resistance values other than 2R and R for the 16 resistors constituting the ladder circuit 18, the change in the output voltage V _I2 with respect to the count value is controlled by the characteristics shown in FIG. 4B or similar thereto. I'm trying to give it some characteristics. As a result, the change in the amount of light per unit bit of the counter 13 can be made substantially constant, and the linear characteristic shown in FIG. 4C can be obtained.

As described above, the present invention stores the aperture value at the time of automatic aperture adjustment as a count value of a counter, and continuously outputs the aperture value voltage corresponding to the count value at the time when the aperture lock starts and the aperture position detection means. The obtained voltage corresponding to the size of the aperture of the aperture is compared by a voltage comparison circuit, and the aperture adjustment motor is controlled based on the comparison result. Therefore, since the aperture lock can be electrically performed using both digital technology and analog technology, the operation is stable and there is no error. In particular, since the aperture value can be accurately stored without changing over time or due to fluctuations in power supply voltage, the aperture lock state can be accurately maintained for a long period of time without any problems.

Further, a counter for counting a predetermined input frequency is periodically reset by a reset signal synchronized with a video signal obtained from the imaging means. Therefore, since the timing of the reset can be synchronized with the video signal obtained from the imaging means, the aperture value during automatic aperture adjustment, which is stored as the count value of the counter, can be made highly reliable. .

Furthermore, when the counter value of the counter is converted into an aperture value voltage by a voltage conversion/correction circuit, the relationship between the aperture value and the amount of incident light is corrected so that the change in the amount of light per unit bit is approximately constant. Therefore, since the relationship between the aperture value and the amount of incident light can be electrically corrected, this correction can be performed stably and accurately, and is more effective than conventional mechanical corrections. It is easy to configure, especially
Remote control becomes very easy.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention,
FIG. 2 is a timing chart illustrating the operation of the counter in FIG. 1. FIG. 3 is a circuit diagram showing a second embodiment of the present invention, FIG. 4 is a diagram showing aperture characteristics and inverse characteristics for correction, and FIG. 5 is a circuit diagram showing an embodiment of a ladder circuit. . In addition, in the symbols used in the drawings, 1... image pickup tube (imaging means), 2... aperture, 3... aperture adjustment motor, 4... aperture, 8... detection circuit (level detection circuit), 9, 12...Voltage comparison circuit, 10...
... variable resistor (aperture position detection means), 13 ... counter, 17 ... latch circuit, 18 ... ladder circuit (voltage conversion/correction circuit).

Claims (1)

[Scope of Claims] 1. A diaphragm provided in the imaging means, a motor that adjusts the size of the aperture of the diaphragm, and diaphragm position detection means that outputs a voltage corresponding to the size of the aperture of the diaphragm. a level detection circuit that detects the level of the video signal obtained from the imaging means, a counter that counts a predetermined input frequency and is reset by a reset signal synchronized with the video signal, and a light amount change per unit bit that is almost constant. a voltage conversion/correction circuit that corrects the relationship between the aperture value and the amount of incident light so that the counter value of the counter is converted into an aperture value voltage; and an output voltage from the aperture position detection means and the voltage conversion circuit. and a voltage comparison circuit that compares the aperture value voltage from the aperture value voltage from the aperture value voltage, and during automatic aperture adjustment, the motor is controlled by the output signal obtained from the level detection circuit to perform automatic adjustment of the aperture value, and the aperture value is automatically adjusted. The counter is configured to be reset periodically by the reset signal, and when a command is issued to maintain the size of the aperture of the diaphragm almost constant during the automatic diaphragm adjustment, the counter is reset by the level detection circuit. The control of the motor by the output signal of is stopped, and the motor is controlled by the output signal obtained from the voltage comparison circuit in which the relationship between the aperture value and the amount of incident light is corrected, so that the aperture is adjusted. An aperture adjustment device for an imaging means configured as shown in FIG.