JPH0638639B2 - Automatic focusing device - Google Patents

Description

The present invention relates to an automatic drive system for detecting a high frequency component of a signal obtained from an image pickup device of a television camera and driving a lens focus matching device so as to maximize its amplitude. The present invention relates to a focus adjustment device.

Configuration of Conventional Example and Its Problems As a conventional technique, there is a method of emitting infrared rays toward a subject, receiving infrared rays reflected from the subject, measuring a distance to the subject, and driving a lens focusing device according to the distance. is there. Although this method has a fast response speed, it requires accurate assembly of the lens focus matching device in order to accurately measure the distance to the subject and drive the lens with the output.

There are also prior art techniques that place the matching device in the feedback loop of an autofocus system to roughen the accuracy of the matching device. That is, the subject image formed on the light receiving surface of the image sensor is periodically and optically blurred to detect the amount of blur, and the amplitude of the high-frequency component signal obtained from the image sensor is maximized. It drives the lens focus matching device, and by placing the lens focus matching device in the feedback loop of the autofocus system, the accuracy of the matching device can be roughened, but the system response due to the time lag of the motor response There was a drawback that I couldn't do it quickly.

The conventional example will be described in detail. FIG. 1 shows a conventional example in which a focus adjusting device for a lens is put in a feedback loop of an autofocus system. In FIG. 1, 1 is a lens, 2 is an image pickup tube for converting optical information of an object into an electric signal, 3 is a pre-amplifier for increasing the electric signal obtained from the image pickup tube 2, 4 is gamma correction, and blacking (BLK) processing, synchronization signal (SYN
A television signal is obtained by a process circuit that performs addition of C). Reference numeral 5 denotes a sync signal generation circuit, which supplies a sync signal (SYNC), a blacking signal (BLK), a vertical drive signal (VD), a horizontal drive signal (HD), etc. to each circuit. Reference numeral 6 is a deflection circuit for scanning the electron beam of the image pickup tube 2. 7 is a circuit for detecting high frequency components, for example, a center frequency of 1 MHz
Is a bandpass filter of. A motor 12 is used to finely move the lens focus matching device with a signal obtained from the reference frequency generating circuit 8 to change the focus of the lens to such an extent that it cannot be detected by the eye. As a result, the output signal of the high-frequency component detection circuit 7 slightly changes the focus, and thus includes the change component. Reference numeral 10 is a circuit for detecting the change component, that is, the reference frequency component. The synchronous detection circuit 9 detects the polarity and amplitude of the reference frequency component signal, and in addition to the motor drive circuit 11, outputs the output signal of the image pickup tube 2. The motor 12 is driven so that the amplitude of the high frequency component becomes maximum.

The detection of the driving direction of the motor 12 will be described with reference to FIG. When the lens focus matching device is driven from a short distance to a long distance and an object is present at the distance D ₁ , the amplitude of the high frequency component signal is as shown in FIG. a ₁ and a ₂ indicate the slight fluctuations of the motor. When it is adjusted to a short distance from the subject, the signal of the reference frequency component is a waveform signal such as b ₁ , and when it is adjusted to a long distance, a waveform signal such as b ₂ is obtained. The motor 12 is driven in the arrow direction of c ₁ by the signal obtained by synchronously detecting the signal of b ₁ . Further, with the b ₂ signal, the motor 12 is driven in the direction of the c ₂ arrow, so that it is stable at the maximum value of the amplitude. In this way, the focus matching device of the lens can be placed in the feedback loop, so the accuracy of the focus matching device can be rough. However, since the motor drives the lens, the response is not fast. In order to speed up the focus, it is necessary to increase the loop gain of the system. When the loop gain is increased, the inertia of the motor causes a hunting phenomenon, which deteriorates the stability of the system. Also, if the loop gain is set high, the motor is shaken due to noise. Therefore, when the focus is matched, the motor is shaken, the image is blurred, and the stability is deteriorated.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an automatic focusing device which has a high response speed and improves stability, except for the above problems.

The present invention relates to a device for changing the optical path length by synchronizing an optical path between an image pickup device and a subject to a reference frequency, a circuit for detecting a reference frequency component signal from an electric signal converted by the image pickup device, and a lens focus matching device. The feedback system is configured so that the focus is adjusted by and when the amplitude of the output signal of the detection circuit is t seconds (n> t) or more and a predetermined amplitude or less in a certain period (n seconds), the loop gain of the feedback loop. , And after reducing the loop gain,
It is an automatic focus matching device that returns the reduced loop gain to the original loop gain when the image of the object being formed changes.When the focus is out of focus, a large loop gain is used to increase the response speed and focus. If the two match, the loop gain is reduced, the hunting phenomenon is prevented, the image blurring due to noise is prevented, and the system stability is improved.

Description of Embodiments One embodiment of the present invention is shown in FIG. 3 and will be described below. Third
1 to 12 in the figure are the same as the constituent elements in FIG. 1 and operate in the same manner. The reference frequency component signal becomes small when the focus is substantially in agreement, that is, when it is near D _{1 in} FIG. This is used to detect that the focus is almost in-focus. This detection circuit is the level detection circuit 13 of FIG. 3, and when the level of the output signal of the reference frequency component detection circuit 10 is below a certain value, the gain of the gain control circuit 14 is lowered. Alternatively, a signal for stopping the motor is generated. That is, when the output signal of the reference frequency component detection circuit 10 is large, the loop gain of the system is increased so as to increase the response speed of the system, and when the output signal of the reference frequency component detection circuit 10 becomes a certain value or less, the loop gain is changed. Make it smaller so that it is in focus without hunting.

Next, an embodiment for improving the stability against noise after focusing is shown in FIG. 4 and described. 1 to 4 in FIG.
13 is the same as the components 1 to 13 in FIG. 3 and operates in the same manner. In this embodiment, the level detection circuit 13
When the level of the output signal of is less than the predetermined value for a certain period of time, the loop gain of the autofocus system is lowered and the state is maintained. When the focus is achieved, the loop gain is in a small state, so that it is stable against noise. The timer 15 and the counter 16 detect whether or not the level of the output signal of the level detection circuit 13 is substantially lower than a predetermined level for a certain period. Timer 15
A timer circuit that determines a required period starts operation when the level of the output signal of the level detection circuit 13 falls below a certain value. The counter 16 counts the number of times when the level of the output signal of the level detection circuit 13 is a certain value or more and becomes a certain value or more. Counter 1 during operation of timer 15
If the count number of 6 is less than a certain value, it is considered that the level of the output signal is substantially less than the predetermined value, and the focus is determined to be in agreement. With such a configuration, it is possible to detect focus matching without being affected by noise. When the synthesis of the focus is detected, the control circuit 17 lowers the gain of the gain control circuit 21 and holds the state. While the state where the loop gain is lowered is held and the focus is deviated when the camera is moved or the subject is moved, it takes time until the focus is matched when the loop gain is small. Therefore, it is necessary to return to the previous state. The detection circuit 18, the hold circuit 19 and the comparator 20 obtain a reset signal for restoration. That is, when the subject moves, the level of the output signal of the high frequency component detection circuit 7 changes, so this is detected and a reset signal for restoration is obtained. I will explain this in detail.

The detection circuit 18 converts the level of the output signal of the high frequency component detection circuit 7 into a DC component. Next, the counter 16 outputs a signal for lowering the loop gain, and at the same time, the detection circuit 18
The output signal of 1 is held by the hold circuit 19. If the camera is not moved and the object is not moved from this state, the output signals of the detection circuit 18 and the hold circuit 19 have the same level, and the output signal of the comparator 20 is zero. When the camera or the subject moves, the output signals of the detection circuit 18 and the hold circuit 19 have different levels, and the output signal of the comparator 20 is obtained. This output signal resets the control circuit 17 to restore the loop gain. In the specific example of FIG. 4, the reset signal is obtained by detecting the change in the high frequency component signal, but the reset signal may be obtained by detecting the change in the video signal.

EFFECTS OF THE INVENTION As described above, in the apparatus of the present invention, the focusing device of the lens is also included in the feedback loop of the autofocus system, so that the focusing is highly accurate and, for example, a 12 × zoom lens can be used. It can also be used with a plastic lens that expands and changes its focus depending on temperature. In addition, the response speed of this system can be increased, and the stability of focus synthesis can be improved.
Moreover, it is stable against noise when focused. As described above, the present invention has an extremely excellent effect.

[Brief description of drawings]

FIG. 1 is a block diagram showing a conventional automatic focusing device, FIG. 2 is a principle diagram for explaining the principle of detecting the driving direction of a motor, and FIG. 3 is an automatic focusing device according to one embodiment of the present invention. FIG. 4 is a block diagram of an automatic focusing device according to another embodiment of the present invention. 1 ... Lens, 2 ... Image pickup tube, 7 ... High frequency component detection circuit, 9 ... Synchronous detection circuit, 10 ... Reference frequency component detection circuit, 13 ... Level detection circuit, 15 ... Timer, 16
...... Counter, 17 ...... control circuit, 19 ...... hold circuit, 20 ...... comparator, 21 ...... gain control circuit.

Claims (1)

[Claims] 1. A device for changing an optical path length between an image pickup device and an object in synchronization with a reference frequency, a high frequency component detection circuit for detecting a high frequency component of an electric signal converted by the image pickup device, and the high frequency component detection. A reference frequency component detection circuit for detecting a reference frequency component from the output signal of the circuit, a drive direction determination circuit for determining the drive direction of the lens focus matching device from the output signal of the reference frequency component detection circuit, and the drive direction determination circuit A drive circuit for moving the lens in the in-focus direction by the output signal of and a gain control circuit inserted between the image sensor and the reference frequency component detection circuit form a feedback loop, and the output of the reference frequency detection circuit When the amplitude of the signal is t seconds (n> t) or more and a predetermined amplitude or less within n seconds, the gain of the gain control circuit is decreased. Point matching device.