JPH02224475A - Automatic focusing detector - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention "Field of Application in Naval Service" The present invention relates to an automatic focus detection device that automatically obtains a focused point by moving a photographing lens based on the high frequency component of a video signal from an imaging means. It is related to.

"Prior art" As a conventional automatic focus detection device of this type, for example, rN
HK Technology Research” Volume 17, No. 1, Published in 1965, r
As shown in the paper ``Automatic focus adjustment of television cameras using mountain climbing servo system'', a method has been proposed that uses the principle of automatically finding the focal point based on the high frequency components of the video signal.

This type of automatic focus detection device focuses on the fact that the higher the optical image of the subject becomes, the higher the high frequency component of the video signal increases, and the focus point is set at the position of the photographing lens where this high frequency component has the maximum value. .

Many automatic focus detection devices employing the above principle have been proposed that use a delay difference detection circuit in order to obtain high frequency components from video signals.

(For example, Special Publication No. 58-708, Special Publication No. 58-709
This type of automatic focus detection device includes a photographing lens, an imaging means, a signal processing means, and a lens driving means.

The imaging means is configured to take out an optical image taken in through a photographing lens as a video signal at a constant clock frequency, and the signal processing means takes in a video signal from the imaging means and extracts a delay difference from the video signal. A circuit configuration is adopted in which a high frequency component is extracted by a detection circuit and a focus detection signal is formed based on the high frequency component.

Further, the lens driving means is configured to move the photographing lens in accordance with a control signal from the signal processing means so that the focus detection signal shows a maximum value.

According to such an automatic focus detection device, an optical image of a subject captured through a photographing lens is converted into a video signal by the imaging means at a constant clock frequency. This video signal is taken into the signal processing means, and a high frequency component is extracted by the delay difference detection circuit. The signal processing means generates a focus detection signal based on the above-mentioned high frequency component and supplies the control signal to the lens driving means. The lens driving means can obtain an in-focus point by moving the photographic lens according to a control signal from the signal processing means until the focus detection signal shows a maximum value.

``Problem to be Solved by the Invention'' In the case of an automatic focus detection device that employs a delay difference detection circuit as described above, a video signal is obtained using a constant clock frequency, but this clock frequency wraps around the delay difference detection circuit. This method has a disadvantage in that it may cause trouble in focusing point detection.

The present invention was developed in order to eliminate the above-mentioned drawbacks, and an object of the present invention is to provide an automatic focus detection device that eliminates the influence of a certain frequency for obtaining a video signal for one in-focus point detection.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides an imaging means for extracting an optical image taken in through a photographing lens as a video signal at a certain frequency, and a video signal from the imaging means. a signal processing means that extracts a high frequency component from the video signal using a delay difference detection circuit and forms a focus detection signal based on the high frequency component; In the automatic focus detection device, the signal processing means is configured to adjust the null frequency of the delay difference detection circuit to the constant frequency. We propose an automatic focus detection device characterized by the following features.

"Operation" The optical image captured through the photographic lens is converted into a video signal with a constant frequency by the imaging means. This video signal is taken into the signal processing means, and a high frequency component is extracted by the delay difference detection circuit. At this time, since the certain frequency is matched to the null frequency of the delay difference detection circuit, it cannot pass through the delay difference detection circuit. Further, the high frequency component necessary for in-focus point detection passes through the delay difference detection circuit with almost no attenuation. The signal processing means forms a focus detection signal based on the high frequency component obtained through such a delay difference detection circuit, and supplies a control signal to the lens driving means in accordance with this focus detection signal. The lens driving means moves the photographing lens according to the control signal from the signal processing means until the focus detection signal shows a maximum value, thereby bringing the focal point to a focused point without being affected by the above-mentioned constant frequency. Obtainable.

"Example" Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of an automatic focus detection device according to the present invention, FIG. 2 is a waveform diagram showing frequency characteristics of a video signal found in a conventional automatic focus detection device, and FIG. 3 is a block diagram showing an embodiment of the automatic focus detection device according to the present invention. FIG. 3 is a waveform diagram showing frequency characteristics of an example delay difference detection circuit.

The automatic focus detection device shown in FIG. 1 includes a photographing lens 1, an imaging means 3, a signal processing means 5, and a lens driving means 7. The imaging means 3 includes an imaging element (for example, a COD element) 31 and an imaging circuit 32. The image pickup means 3 is configured such that an optical image formed on the image pickup element 31 via the photographing lens 1 can be extracted as a video signal SO by the image pickup circuit 32 at a constant rotation lock frequency.

As can be understood from FIG. 2, the signal level of the video signal SO obtained in this manner decreases as the frequency f (MHz) on the horizontal axis increases.

The signal level is high again at frequency fo.

This frequency fO is noise that appears due to the clock frequency when reading the video signal SO from the image sensor 31.

Further, in FIG. 2, the imaging signal So is the signal when the image is in focus, and the video signal S02 is the signal when the image is out of focus.

Further, the signal processing means 5 receives the video signal S from the imaging means 3.
A gate circuit 51 that takes in O and a delay difference detection circuit 52
, a gate circuit 53 , an absolute value circuit 54 , a peak value detection circuit 55 , an A/D converter 56 , and a microprocessor 57 .

The delay difference detection circuit 52 includes a delay circuit 521 that delays the signal by a certain time (τ), an inverter 522 that inverts the phase of the signal, and an adder 523 that adds the signal from the delay circuit 521 and the signal from the inverter 522. Consisting of

The transfer function IT(ω) of such a delay difference detection circuit 52
1, the delay time of the delay circuit 521 is τ, and the angular frequency is ω(
2πf), and fo is the clock frequency, it is given by IT (ω)l=1-costω).

Transfer function IT(ω) obtained in this way! has the characteristics as shown in FIG.

And what is the delay time τ and the clock frequency fo?

This is done so that τ=n/fo (n=0, 1, 2...) holds true.

This causes the null frequency of the delay difference detection circuit 52 to match the clock frequency fO.

In the signal processing means 5, the video signal So taken in via the gate circuit 51 is supplied to a delay difference detection circuit 52. The delay difference detection circuit 52 adjusts its null frequency to the successive clock frequency fo as described above. Therefore, the high frequency component output from the delay difference detection circuit 52 does not include the clock frequency.

In this way, the high frequency component not including the clock frequency is given to the absolute value circuit 54 via the gate circuit 53. Note that the above-mentioned gate circuit specifies the area where the focus is to be aligned.

The signal obtained via the absolute value circuit 54 is supplied to a peak value detection circuit 55 to detect the peak value. The peak value detected by the peak value detection circuit 55 is A
The focus detection signal Sa is supplied to the microprocessor 57 via the /D converter 56, and a control signal Sc corresponding to the focus detection signal is output.

The lens drive means 7 includes a motor drive circuit 71 that generates a motor drive signal based on the control signal Sc, and a motor 72 that is driven by the motor drive circuit 71 to move the photographing lens 1.

This lens driving means 7 is configured to input the control signal Sc from the signal processing means 5 into a motor driving circuit 71 and drive the motor 72 until the above-mentioned focus detection signal Sa shows the maximum value.

The operation of the embodiment configured as described above will be explained.

An optical image of a subject formed on the image sensor 31 via the photographic lens 1 is extracted by the image pickup circuit 32 as a video signal So at a constant clock frequency fo.

Further, the video signal SO from the imaging means 3 is transmitted to the gate circuit 5.
1 to the delay difference detection circuit 52. In the delay difference detection circuit 52, the video signal SO is transferred to the delay circuit 521.
The signal is delayed by a certain period of time (τ) and supplied to the addition WI 523.

On the other hand, the video signal So has its phase inverted by an inverter 522 and is supplied to an adder 523. Adder 5
At 23, the difference between these signals is extracted.

By the way, the delay difference detection circuit 52 described above has a filter characteristic as shown in FIG. does not include the clock frequency fo.

The signal components necessary for the in-focus point are the video signals So, .
As can be seen from So, since it is concentrated in 1 to 3 (MHz), no problem occurs. The high frequency component thus obtained from the delay difference detection circuit 52 is transmitted to the gate circuit 5.
3 to the absolute value circuit 54.

The signals converted into absolute values by the absolute value circuit 54 are supplied to a peak value detection circuit 55 to detect the peak value of each signal.

The peak value detected and held by the peak value detection circuit 55 is supplied to the microprocessor 57 as the focus detection signal Sa via the A/D converter 56, and is controlled to indicate the maximum value of the focus detection signal Sa. A signal Sc is output.

The control signal Sc is a signal for driving the motor 72 in the motor drive circuit 71. This drive signal causes the motor drive circuit 71 to rotate until the focus detection signal Sa reaches its maximum value, thereby moving the photographing lens 1 to the in-focus position.

This embodiment operates as described above.

Focusing can be done automatically without being affected by the clock frequency fo.

"Effects of the Invention" As described above, the present invention eliminates the influence of this frequency contained in the video signal by matching the null frequency of the delay difference detection circuit of the signal processing means to the frequency for obtaining the video signal. In-focus point detection can be performed using the focus detection signal, which is extremely advantageous in improving focus alignment accuracy.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a waveform diagram showing frequency characteristics of a video signal in a conventional automatic focus detection device, and Fig. 3 is a delay difference provided in the signal processing means of the above embodiment. FIG. 3 is a waveform diagram showing frequency characteristics of the detection circuit. 1...Photographing lens 3...Imaging means 5...Signal processing means 7...Lens driving means 52...Delay difference detection circuit

Claims (1)

[Claims] an imaging means for extracting an optical image taken in through a photographing lens as a video signal with a certain frequency; and a video signal from the imaging means is taken in, a delay difference detection circuit extracts a high frequency component from the video signal, and the high frequency component is extracted from the video signal by a delay difference detection circuit. a signal processing means for forming a focus detection signal based on the
In the automatic focus detection device, the signal processing means includes a lens driving means for moving a photographing lens so that the focus detection signal shows a maximum value in response to a control signal from the signal processing means, the signal processing means An automatic focus detection device characterized by having a configuration in which the null frequency of the detection circuit is matched to the above-mentioned constant frequency.