JPS58188966A - Automatic focus matching device - Google Patents

Abstract

PURPOSE:To match the focus of a lens so that the output signal of arithmetic processing has maximum amplitude and to stabilize operation, by inputting a video signal from an image pickup element to plural BPEs having different bands, and processing the output signals of the BPFs. CONSTITUTION:A motor 12 for driving the focus matching device of the lens 1 is driven minutely by the output of a reference signal generating circuit 10 for minutely moving the focus matching device to cause invisible variation of the high frequency component of the output signal of the image pickup tube 2. This variation of the high frequency component is detected by the BPFs 13 and 14 for obtaining high frequency component signals differing in center frequency, and their outputs are processed by an processor circuit 15. When the output signal of the BPF14 having the high center frequency exceeds a certain level, a feedback loop is constituted by the output of the BPF13 and the focus matching device of the lens 1 is driven so that the output signal of the arithmetic processing circuit 15 has maximum amplitude.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic focusing device that detects a high frequency component of a signal obtained from an image sensor of a television camera and drives a lens focusing device so that its amplitude is maximized. It is.

As a conventional technique, there is a method in which a high frequency component is detected by passing a signal obtained from an image sensor through a band-pass filter, and a focusing device of a lens is driven so that the detected signal is maximized. However, when the lens aperture is wide open or close to it, and the distance to the subject is misaligned with the position of the lens focusing device, the image on the light-receiving surface of the image sensor is blurred, and high-frequency components are As a result, the automatic focusing device malfunctions.

The present invention provides a highly accurate automatic focusing device that prevents the above-mentioned malfunctions.

The conventional technology will be explained using FIG. 1. 1
is a lens with a focusing device, and this device is driven by 12 motors. 2 is an image pickup tube that converts optical information of the subject into an electrical signal, 3 is a preamplifier that amplifies the output signal of the image pickup tube 2, and 4 is a gamma correction.

A process circuit that performs blanking processing, addition of synchronization signals, etc. converts the electrical signal into a television signal. 6
is a synchronization signal generator that generates synchronization signals, blanking signals, vertical drive signals, horizontal drive signals, etc. A deflection circuit 6 deflects the beam from the image pickup tube 2. Reference numeral 10 is a band pass filter (BPF) for extracting high frequency components of the video signal, reference frequency generation circuit 10 is used to periodically slightly change the focus of the lens 1, and motor drive circuit 11. motor 12
, the focusing device of the lens 1 is moved slightly, and the focus is slightly changed to the extent that it cannot be detected by the eye. As a result, the output of the BPF slightly changes with the period of the reference frequency. The reference frequency component detection circuit 8 detects only the reference frequency component of the output of the BPF 7. This signal and the reference frequency signal of the reference frequency generating circuit 1o are synchronously detected to detect the driving direction of the motor 12, and a feedback loop is constructed so that the amplitude of the output signal of the BPF 7 is maximized.

Next, the driving direction of the motor 12 will be explained with reference to FIG.

When the subject is at a distance of Dl, the amplitude characteristic of the output signal of the BPF7 when changing the focusing device to a short distance is expressed as a second
The figure shows. When the distance is adjusted to be shorter than Dl, the focus is created by the motor 12. This signal is synchronously detected and the output signal is used to move the focusing device in the direction of the arrow 01. Then, when the focus adjustment device is adjusted to a distance farther than Dl, the output signal of BPF 7 changes as shown in b2, so the synchronous detection output has the opposite polarity than above, and the focal point The matching device moves in the direction of the arrow C2 and, as a result, stabilizes at the point Dl where the output signal of BPF 7 becomes maximum. Since the lens system is also included in the feedback loop, the accuracy of focusing is very high, but if the distance to the subject and the distance at the lens focusing device deviate,
The output of the BPF 7 becomes very small and the noise becomes large, resulting in malfunction.

In the present invention, when the focus adjustment of the lens is severely distorted,
By arithmetic processing the output signals of the BPF with a high center frequency and the BPF with a low center frequency, the driving direction of the lens focusing device can be found, and the deviation of the focus adjustment of the lens can be minimized. The BPF is driven so that its output signal is maximized to eliminate malfunctions.

BPFl with a low center frequency and BPF2 with a high center frequency
Figure 3 shows the characteristics of the output signal.

The output signal of BPFl is very broad, so the detection range is very wide. Therefore, when the output signal of BPF2 is small, the autofocus feedback loop is configured with the output of BPFl, and when the amplitude of the BPF2 output signal exceeds a certain value, the output is configured to configure the autofocus feedback loop. .

A basic embodiment of the invention is shown in FIG.

1 to 6 and 8 to 12 operate in the same way as the same numbers in FIG. That is, the motor is caused to move slightly at the reference frequency, and the high frequency component of the electric signal obtained by the image pickup tube 2 is changed to an invisible degree. Then, the cylindrical frequency component is detected by two bandpass filters 13 and 14 having different center frequencies. One bandpass filter 13 has a low center frequency, for example, a band of 200 KHz to I MHz.
It has the characteristics shown in BPFl in FIG. That is, the detection range is very wide, but the detection sensitivity is poor.

The other bandpass filter 14 has a high center frequency, for example, a band of 15 MHz to 26 MHz, and has characteristics as shown by BPF2 in FIG. 3. In other words, the detection range is narrow, but the detection sensitivity is excellent.

16 is an arithmetic processing circuit, and when the lens is out of focus and the image is blurred, the output of the bandpass filter 14 is very small, so the output of the bandpass filter 13 forms a feedback loop. Pass filter 1
If the output of 4 is above a certain level, the output is used to form a feedback loop.Next, a specific example of the arithmetic processing circuit 15 is shown in FIG.

D1 in the figure. D2 is a diode, C1 and C2 are capacitors, and band pass filter BPF1. It constitutes a peak rectifier circuit that rectifies the peak value of the output signal of BPF2,
The changing component of the reference frequency signal of the circuit 1o in FIG. 4 has a time constant that is not smoothed. 17 is a comparator, and when the output of BPF2 exceeds a certain amplitude, the output signal C8 becomes high level. 016 is an analog switch, and when the output signal C0 becomes high level, the input signal 1.2
becomes the output signal of the analog switch, and when co is at low level, the input signal becomes the output signal of the analog switch 16. In this way, when the output signal of BPF2 is small, the output signal of BPF1 constitutes the feedback loop of the automatic focusing device, and when the output signal of BPF2 exceeds a certain amplitude, the output signal constitutes the feedback loop. I come to do it.

Next, FIG. 6 shows a specific example of a means for achieving focus matching with even higher precision. In the figure, 18, 19, 20° 21 are bandpass filters whose center frequencies are different and whose bands overlap each other; the center frequencies are 18, 19, 20.
21 is the highest. 22, 23, and 24 are comparators that output the output signals I6. I.

When I4 exceeds a certain level, output signals C3 and C2°C1 become high level. 26 is a discrimination circuit; when C3 is at a high level, C2 is selected; no matter what level C1 is, C3 is selected.
It drives 26 analog switches so that priority is given to C1 at any level, C2 at any level.

In other words, when a signal with a higher frequency component exceeds a certain level, priority is given to it and a feedback loop is formed.

Another example of a method for detecting high frequency components is shown in FIG.

18 to 21 are band-pass filters with different center frequencies, respectively, as in FIG. 6, and their respective outputs are connected to resistors R3,
Add using R4, R6, and R6. At this time, output signals with high center frequencies are weighted and added together so that they become larger.

As described above, according to the present invention, the detection range is expanded to detect high frequency components of the image, and the lens focusing device is also included in the feedback loop, so that an extremely highly accurate automatic focusing device can be constructed. In other words, even if the accuracy of the focusing device is rough, or even if the focus changes slightly due to temperature like a plastic lens, the focusing device remains stable as a system.

In addition, since the feedback loop is configured with a signal detected as a high-frequency component signal with good focusing accuracy, it has extremely outstanding functions and effects, such as becoming a highly accurate automatic focusing device.

One example of the present invention has been described using a method in which the focusing device of the lens is slightly moved by a motor to slightly blur the image formed on the image sensor. It is also possible to apply a method in which the optical path length is varied by inserting a glass and varying the degree of inclination of the glass.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an example of a conventional automatic focusing device, FIG. 2 is a characteristic diagram for explaining the operation of FIG. 1, FIG. 3 is a characteristic diagram of the BPF used in the present invention, and FIG. A block diagram of an automatic focusing device according to an embodiment of the invention, FIG. 6, FIG. 6, and FIG. 7 are block diagrams each showing a specific example of the main part of the invention. 1...Lens with a focusing device, 2...
...Image tube, 1o...Reference signal generation circuit for slightly moving the lens focusing device at low frequency, 12...
. . . A motor that drives a lens focusing device, 13° 14 . . . A bandpass filter that obtains a high frequency component signal, 15 . . . Arithmetic processing circuit. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 Figure 3 Figure 4 Figure 5/l Figure 6 Figure 7/8

Claims (2)

[Claims] (1) The video signal obtained from the image sensor is input to multiple bandpass filters with different bands, and the output signals of each of the bandpass filters are processed, and the amplitude of the processed output signal is maximized. An automatic focusing device characterized by driving a lens focusing device. (2) When the output signal of the band pass filter with the highest center frequency among the plurality of band pass filters exceeds a certain level, the output signal is used to drive the focusing device of the lens. An automatic focusing device as claimed in claim 1.