JPH0628397B2 - Optimal beam focus detection method for image pickup tube - Google Patents

Description

TECHNICAL FIELD The present invention relates to detection of an optimum electron beam focus state of an image pickup tube.

(Prior Art) In order to obtain an optimum focus state by adjusting the electron beam focus of a conventional image pickup tube, an image of a subject that shows whether the beam focus is good or bad is picked up by the image pickup tube and displayed on a display device such as a CRT. Then watch this and adjust the beam focus circuit of the image pickup tube so that the image of the object is the sharpest, or display the output waveform of the image pickup tube on an oscilloscope etc. We have adjusted the optimal beam focus point so that it is maximized.

However, in such a method, it is necessary to capture an image of a subject having a high frequency component (such as a specially prepared test chart) that allows the quality of the beam focus to be recognized, and it is difficult to capture such a subject. Under the circumstances (for example, on-site shooting with a mini handy camera), it was difficult to quickly and accurately find the optimum beam focus of the image pickup tube.

(Main points of the invention) The present invention solves the above-mentioned conventional problems and eliminates the drawbacks, and a simple method for determining the optimum electron beam focus state of an image pickup tube without requiring a specially prepared subject.
It seeks to detect quickly and accurately.

That is, the optimum beam focus detection method for an image pickup tube according to the present invention superimposes a high-frequency signal on the deflection wave voltage or current of the image pickup tube and applies it to the image pickup tube. When the voltage is applied, it appears in the image output signal of the image pickup tube. An optimum electron beam focus state of the image pickup tube is detected by extracting an output signal having the same frequency as the high frequency signal and detecting the extracted output signal as the maximum output.

(Example) Hereinafter, the present invention will be described in detail with reference to the drawings.

The present invention relates to a deflection wave of an image pickup tube (deflection voltage in the electric field deflection method,
Focusing on the fact that in the magnetic field deflection method, the noise mixed in the deflection current) appears more as noise in the video signal when the beam focus is better, the minute high frequency signal is applied to the deflection wave, and at that time the minute It is intended to detect the best beam focus point by maximizing the signal of the high frequency signal.

FIG. 1 shows an embodiment of an apparatus used in the optimum beam focus detection method for an image pickup tube of the present invention. In FIG. 1, reference numeral 6 denotes a micro high frequency oscillator, which has a frequency f _s output by the oscillator.
The small high-frequency signal (several MH _Z), in addition to the deflection wave output from the deflection amplifier 2 by the adder circuit 5, which the deflection electrode of the image pickup tube in the case of the field deflection, the deflection in the case of magnetic deflection Apply to the coil. At this time, if light is incident on the surface of the imaging tube and appropriate charges are accumulated, the effect of the added minute high frequency signal is superimposed on the image output signal as a signal of the same frequency f _s . Hereinafter, this signal is referred to as a "deflected video signal". This deflected video signal depends on the degree of beam focus, and has the maximum output at the optimum beam focus point.

The above-mentioned video output signal on which the deflection video signal is superimposed is passed through a bandpass filter 7 having a pass band f _s to extract the deflection video signal output by a minute high frequency signal, and the focus power supply 3 is set to the focus power supply so that the deflection video signal output becomes maximum. It is controlled by the control circuit 8.

Next, the procedure of detecting the beam focus best point according to the present invention will be described.

Generally, the deflection video signal shows a peak at a specific voltage or current value when the voltage of the focus power supply is changed in the case of electric field deflection and the current of the focus power supply is changed in the case of magnetic field deflection.

Therefore, to obtain the optimum beam focus point, first change the voltage or current of the focus power supply, and if the deflection video signal increases, change the focus voltage or current in the same direction to the point where this decreases. Detects the maximum point of the deflected video signal. On the contrary, when the deflection video signal decreases with respect to the change of the voltage or current of the focus power supply, the change of the voltage or current of the focus power supply is reversed and the voltage or current of the focus power supply that maximizes the deflection video signal is obtained. Ask for.

The band pass filter 7 is not always necessary if the design is so-called flat.

The minute high-frequency signal is usually applied only when adjusting the beam focus, but when it does not affect the image, it can be always applied to obtain the optimum beam focus moment by moment.

The detection method of the present invention can also be applied to so-called dynamic focus. The dynamic focus is to apply a focus voltage or current according to the optimum value of the focus voltage or current depending on the position on the imaging tube surface (the position on the screen). The values to be calculated are stored in advance as a function of the position on the screen by the above method, stored in a memory circuit, and when the above-mentioned stored values are used when the image pickup tube is actually operated, the dynamic focus can be used. The present invention can be applied.

The deflection wave as an image of the present invention may be a horizontal deflection wave or a vertical deflection wave. However, when applied to a vertical deflection wave, the television video signal is a system in which the so-called horizontal scanning precedes, that is, the video signal is configured by repeated horizontal scanning from the top to the bottom of the screen. There is a vote to sample the video signal output at f _h (horizontal scanning frequency). That is, as shown in FIG. 2, signals are vertically extracted from a certain horizontal position in one screen from top to bottom, and the extracted signals are observed. Since the sampling is performed at the frequency of f _h , it must be taken into consideration because the aliasing distortion is generated unless the frequency of the minute high-frequency signal on the vertically polarized wave is less than 1/2 f _h .

(Effect) As is apparent from the above description, according to the detection method of the present invention, it is necessary to image a subject having a high frequency component such as a specially prepared test chart and adjust the beam focus. There is no effect, and there is an effect that adjustment can be performed easily and quickly by a simple method. Therefore, it is particularly effective when it is introduced into a so-called auto set-up type camera of computer control.

Further, in the conventional method, the focus of both the optical system and the electron beam system is related to each other, and it is impossible to adjust and detect only the electron beam system independently. It has become possible to detect only the optimum focus state.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration example of an apparatus used in the optimum beam focus detection method of the present invention, and FIG. 2 is a diagram for explaining screen sampling when the present invention is applied to a vertically polarized wave. 1 ... Image pickup tube, 2 ... Deflection amplifier, 3 ... Focus power supply, 4 ... Image amplifier, 5 ... Addition circuit, 6 ... High-frequency oscillator, 7 ... Band pass filter, 8 ... Focus power supply control circuit.

Claims (1)

[Claims] 1. A high frequency signal is superimposed on a deflection wave voltage or current of an image pickup tube and applied to the image pickup tube. At the time of application, an output signal having the same frequency as the high frequency signal appearing in a video output signal of the image pickup tube is applied. An optimum beam focus detection method for an image pickup tube, characterized in that the optimum electron beam focus state of the image pickup tube is detected by extracting and detecting the extracted output signal as a maximum output.