JPH02288558A - Automatic focusing device - Google Patents

Abstract

PURPOSE:To attain stable and accurate automatic focusing by controlling the phase of a reference frequency signal for fine focusing device and that of a vertical synchronizing signal for a television signal depending on the electric charge storage time and its timing of an image pickup element. CONSTITUTION:A focusing device for a lens 1 is finely adjusted by a motor driving circuit 11 and a motor 12 with a reference frequency signal source 10 synchronously with a vertical synchronizing signal of a standard television signal. A reference frequency component is detected from the high frequency component of a video signal obtained from an image pickup element 2 and the focusing device of the lens is driven with the output being the result of phase comparison between the detected component and the original reference frequency so as to maximize the level of the high frequency component. Then the relation of the phase between the reference frequency signal is varied depending on the charge storage time and its timing of the image pickup element with a phase control circuit 13 so as to obtain the high frequency component with the maximum efficiency. Thus, stable and accurate automatic focusing is attained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an automatic focusing device in a television camera.

2. Description of the Related Art In recent years, automatic focus functions have become important in television cameras in order to improve operability.

The automatic focusing device measures the distance to the subject and drives the lens alignment device accordingly.The automatic focusing device also measures the distance to the subject and drives the lens alignment device accordingly.The automatic focusing device also measures the distance to the subject and drives the lens alignment device accordingly.The automatic focusing device also measures the distance to the subject and drives the lens alignment device accordingly. A method for driving a lens alignment device is known.

As a conventional technique, an example of the latter method will be explained using FIG. 2. Reference numeral 1 denotes a lens with a focusing device, which is driven by a motor 12 . 2 is an image sensor that converts optical information of a subject into an electrical signal; 3 is a preamplifier that amplifies the output signal of the image sensor 2; 4 is a process circuit that performs gamma correction, blanking processing, addition of synchronization signals, etc.; Converts the signal to an old television signal. 6 is a synchronization signal generator, which is a synchronization signal.

Generates blanking signals, vertical drive signals, horizontal drive signals, etc. Reference numeral 6 denotes a scanning drive circuit for the image sensor. 7 is a high frequency component detection circuit (hereinafter referred to as BPF) that extracts the high frequency component of the video signal; 1o is a reference frequency generation circuit for periodically changing the focus of the lens 1; By slightly moving the focusing device, the focus is changed slightly to the extent that it cannot be detected by the eye. As a result, the output of the BPF 7 slightly changes with the period of the reference frequency. B in the reference frequency component detection circuit 8
Only the reference frequency component of the output of PF7 is detected. The phase comparison circuit 9 detects the phase difference between this signal and the reference frequency signal of the reference frequency generation circuit 1°, and the feedback closure circuit is operated so that the amplitude of the output signal of the BPF 7 is maximized by this phase difference output signal. Configure.

Next, determination of the driving direction of the motor 12 will be explained.

FIG. 3 shows how the amplitude of the high frequency component signal changes depending on the position of the lens focusing device when the distance to the object is Dl. That is, the amplitude of the high frequency component decreases whether the focusing device is closer or farther than Dl. Next, when the focusing device is at a position closer than Dl, &1
When the focusing device is changed as shown in FIG. 1, the amplitude of the high frequency component signal changes as bl. This signal is synchronously detected and the motor is driven. The polarity is determined so that the driving direction at this time is C1. When the focus matching device is located at a distance farther than Dl, if the focus matching device is changed as shown in &2, the change in the amplitude of the high frequency component signal becomes b2. Since the polarity of the change in b2 is opposite to the polarity of the change in bl, the driving direction of the motor becomes C2. As a result, the amplitude of the high frequency component signal becomes stable at the maximum point.

Problem to be Solved by the Invention However, in the automatic focusing device of such a television camera, the optical path length from the subject to the image sensor light receiving surface is changed at a reference frequency synchronized with the vertical synchronization signal of the standard television signal. The high frequency detection/detection circuit 7 depends on the phase relationship between the reference frequency and the vertical synchronization signal.
output changes. That is, even if the target is the same, if the reference frequency signal and the vertical synchronization signal are different in phase, the magnitude of the obtained high frequency component changes, causing the automatic focusing device to malfunction.

The present invention solves such conventional problems, and the phase of the reference frequency signal and vertical synchronization signal is adjusted so that the magnitude of the high frequency component is maximized depending on the charge accumulation time of the solid-state image sensor and its timing. The present invention provides an automatic fish gathering and matching device that controls.

Means for Solving the Problems The automatic focusing device of the present invention changes the optical path length from the subject to the light-receiving surface of the image sensor at a reference frequency synchronized with the vertical synchronization signal of the standard TVIL signal, and Detecting a reference frequency component from the high frequency component of the video signal, and driving a lens focusing device so that the level p of the high frequency component is maximized based on the output of comparing this with the basic single frequency, In addition, the phase relationship between the vertical synchronization signal and the reference frequency signal is controlled by the charge accumulation time in the image sensor and its timing, so that the high frequency component of the video signal can be obtained most efficiently.

Operation The automatic focusing device of the present invention controls the phase of the vertical synchronization signal of the standard television broadcast signal and the reference frequency signal synchronized with the vertical synchronization signal by controlling the charge accumulation time in the image sensor and its timing. The high frequency components necessary for focus alignment can be obtained most efficiently, and the automatic focus alignment device can operate stably and accurately.

Embodiments Hereinafter, an explanation will be given with reference to a block diagram of an automatic focusing device according to an embodiment of the present invention.

FIG. 1 shows a block diagram of an embodiment of the invention. In FIG. 1, 1 to 12 are the same elements as in FIG. 2.

A case will be described in which the optical path length from the subject to the light receiving surface of the image sensor is changed by phase control of a vertical synchronization signal of a standard television signal and a reference frequency signal synchronized with the vertical synchronization signal. Normally, in the case of a standard NTSCj signal, the charge accumulation time in the image sensor is 1760 seconds, so if 15) h, which is synchronized with the vertical synchronization signal of the standard television signal, is the reference frequency of the base single frequency signal source 10, the focus High frequency components needed to match most efficiently.

In order to obtain a good signal, it is necessary to set the peak of the reference frequency halfway between the vertical synchronization signal of the standard television signal and the next vertical synchronization signal in terms of time. That is, this is because the necessary high frequency components can only be obtained while the image sensor is accumulating charges. While charges are not being accumulated, there is no fluctuation in high frequency components even if the optical path length is changed. It can be seen that in order to obtain the high frequency component most efficiently, the peak of the reference frequency should be set midway between the vertical synchronizing signals. Further, depending on the special mode, the charge accumulation time and timing in the image sensor may be set during the vertical blanking period of the standard television signal. In this case, if the charge accumulation time and its timing are detected and the peak of the reference frequency is set in the middle of the charge accumulation time as in the theory described above, the high frequency component can be obtained most efficiently. As described above, the image sensor drive circuit 6 detects the special mode, and the phase control circuit 13 determines the phase relationship between the reference frequency signal and the vertical synchronization signal of the standard television signal, and determines the charge accumulation time of the image sensor and its timing. By changing the value, high frequency components can be obtained most efficiently and stable and accurate automatic focusing can be performed.

Effects of the Invention As described above, the automatic focusing device of the present invention changes the optical path length from the subject to the light receiving surface of the image sensor at a reference frequency synchronized with the vertical synchronization signal of a standard television signal, and changes the charge accumulation time of the image sensor. By controlling the phase of the reference frequency signal and the vertical synchronization signal of the standard television signal, high frequency components can be obtained most efficiently and stable and accurate automatic focusing can be performed. It is effective.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an automatic focusing device according to an embodiment of the present invention, FIG. 2 is a block diagram showing a conventional automatic focusing device, and FIG. 3 is a diagram explaining the principle of detecting the driving direction of a motor. . 1...Lens with a focusing device, 2...
...Image sensor, 3...Preamplifier that amplifies the output of the image sensor, 4...Process circuit, 5...
・Image sensor scanning drive circuit and charge accumulation time detection circuit,
6... Synchronization signal generator, 7... Circuit for detecting high frequency components, 8... Reference frequency component detection circuit, 9... Phase comparison circuit, 10... . . . Reference signal generation circuit for finely moving the lens focusing device at the reference frequency, 11 . . . Motor drive circuit, 12.
...Motor, 13...Reference frequency phase control circuit. Name of agent: Patent attorney Shigetaka Awano and one other name
I ry diagram diagram

Claims (1)

[Claims] changing the optical path length from the subject to the light receiving surface of the image sensor at a reference frequency synchronized with the frequency of a vertical synchronization signal of a standard television signal, and detecting a reference frequency component from the high frequency component of the video signal obtained from the image sensor; The automatic focusing device drives the focusing of the lens so that the level of the high frequency component is maximized based on the output of comparing this with the reference frequency, and the automatic focusing device drives the focusing of the lens so that the level of the high frequency component is maximized according to the change in the charge accumulation time in the image sensor. An automatic focusing device comprising: means for controlling the phase of the reference frequency signal that changes the optical path length between the subject and the light receiving surface of the image sensor at the reference frequency.