JPS60217759A - Automatic focal point adjusting device - Google Patents

Abstract

PURPOSE:To prevent the variation of response of a system caused by the fluctuation of the stop and focal length of a lens, by performing detecting and arithmetic processes on at least one of the stopping value and focal length value of the lens, and changing the band of a detected frequency component in accordance with the arithmetic process. CONSTITUTION:The inclination of the mountain-shape characteristic of a high frequency component detected from the output signal of an image pickup element 2 becomes steeper the higher the center frequency of the detected band is. The output of a high-frequency component detecting circuit 13 indicates that the aperture of a lens 1 is stopped down to have a gently inclined mountain-shape characteristic and the output of another high-frequency component detecting circuit 14 indicates that the aperture of the lens 1 is opened to have a steeply inclined mountain-shape characteristic. Therefore, when the focal point adjusting operation is made by using the output of the detecting circuit 13 when the aperture is opened and the output of the detecting circuit 14 when the aperture is stopped down, the loop gain, namely, the response of this system can be made constant to the fluctuation of the aperture in the same operating extent. The same operation is made to the focal length.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is directed to a lens that maximizes the amplitude of high-frequency components of a signal obtained from an image sensor whose image of a subject is formed on the light-receiving surface of a television camera. The present invention relates to an automatic focusing device for driving a focusing device.

Conventional configurations and their problems In recent years, the demand for television cameras has been rapidly increasing due to the spread of multiple video tape recorders and the miniaturization and weight reduction of household use. The automatic focusing device simplifies the handling of television cameras and contributes to their further widespread use.

A conventional automatic focusing device will be explained below.

FIG. 1 shows a block diagram of a conventional automatic focusing device, in which 1 is a lens, 2 is an image sensor that converts the subject image formed on the imaging surface into an electrical signal, and 3 is the image sensor. 2 is a preamplifier that amplifies the output of the preamplifier, 4 is a process circuit that processes the video signal output from the preamplifier and converts it into a television signal, and 5 is a sync signal generator that generates various sync signals and blanking signals. Reference numeral 6 denotes an image winding element drive circuit for driving the image pickup element 2. 7 is a high frequency component detection circuit for detecting high frequency components of the video signal obtained from the image sensor 2; for example, center frequency 1 (MH2);
This is a bandpass filter. 8 is a reference frequency generator that supplies a reference frequency to the motor drive circuit 11 and the synchronous detection circuit 10 and finely moves the lens focusing device using the reference frequency;
9 is a reference frequency component detection circuit that detects a reference frequency component included in the high frequency component; 10 is a synchronous detection circuit that compares the detected reference frequency component with a reference frequency and detects the phase and amplitude of the reference frequency component. , the synchronous detection circuit 1
With an output of 0, the focusing device of the lens 1 is driven by the motor 12 through the motor drive circuit 11 so that the high frequency component is maximized.

The operation of the conventional automatic focusing device configured as described above will be described below.

The motor 12 uses a reference frequency supplied by the reference frequency generator 8 to finely move the focusing device of the lens 1 to change the focus of the lens to an extent that is imperceptible to the eye. As a result, the high frequency component included in the output signal of the image sensor 2 undergoes amplitude modulation at the reference frequency and has a reference frequency component. The high frequency component is detected by a high frequency component detection circuit 7, and the reference frequency component included therein due to focus change is detected by a reference frequency component detection circuit 9. The polarity and amplitude of the signal are detected by a synchronous detection circuit 1o, and the signal is sent to a motor drive circuit 11. A motor 12 drives the focusing device of the lens 1 so that the high frequency component of the output signal of the image sensor 2 is maximized.

Regarding the principle of detecting one driving direction of the motor 12, the second
This will be explained in more detail using figures. The vertical axis is image sensor 2
The horizontal axis is the position of the focusing device of the lens 1. Near is the position where the subject is in focus at a short distance, and far is the position where the subject is in focus at the far distance. Now, if we consider the case where an image of a subject at a distance D1 is taken, the focusing device of the lens 1 is set at the distance D1.
When the object is at a position corresponding to , it is in focus and the amplitude of the high frequency component is at its maximum. If the focusing device moves closer or further away from the above position, the amplitude of the high frequency component will decrease.

This is a kind of chevron-shaped characteristic, as shown in (1) in Figure 2. On the other hand, "11a2+"3 is the motor 1 at each lens position.
2 shows the movement of the focusing device due to micro-movements at a reference frequency of 2. Due to the change in focus accompanying the slight fluctuation shown in a, the high frequency component undergoes amplitude modulation like bl and has a reference frequency component. Further, the slight fluctuation shown in a2 undergoes amplitude modulation shown in b2. Said amplitude modulation 4. As is clear from b2, the phase is reversed by 180° between the near and far sides of the in-focus position. Therefore, a reference frequency component is detected from high frequency components subjected to amplitude modulation such as bl, and the reference frequency component is synchronously detected with the reference frequency to detect the amplitude and phase of the component. If the motor 12 drives the focusing device of the lens 1 in the direction of the arrow c1 using the detection signal, in the case of b2, the focusing device of the lens 1 is driven in the direction of the arrow c2.
It will be driven in the direction of. Therefore, the motor 12 always drives the focusing device to the position where the high frequency component is maximized, and a focused state is obtained. As described above, this conventional automatic focusing device has many features such as being able to form a closed loop including the focusing device of the lens, and making it possible to assemble the focusing device roughly.

However, the above configuration has the following problems. The slope of the chevron-shaped characteristic exhibited by the high frequency component changes depending on the aperture value of the lens 1. Therefore, when the diaphragm is closed, it becomes a gentle slope as shown in FIG. 2(n). In the above state, the reference frequency component obtained with respect to slight fluctuations of the focusing device of the lens 1 is reduced. This conventional automatic focusing device uses a signal obtained by synchronously detecting the reference frequency component at the reference frequency to drive the motor 12.
, and a decrease in the reference frequency component as described above results in a decrease in loop gain and slows down the response. If the loop gain of the system is set to a large value in consideration of the aforementioned decrease due to the change in the aperture, the loop gain of the system will be too large when the aperture is open, and hunting will occur due to the motor time lag, so it cannot be increased. .

Television cameras often photograph moving subjects, and the response is critical.

A similar thing happens with a zoom lens that can change its focal length due to changes in its depth of focus.

OBJECTS OF THE INVENTION The present invention solves the above-mentioned conventional problems, and aims to provide an automatic focusing device whose response does not change due to changes in lens aperture or focal length.

Structure of the Invention The present invention detects frequency components having one or more different bands from a signal obtained from an image sensor on which a subject image is formed on the light-receiving surface, and detects frequency components having one or more different bands so that the amplitude of the frequency component is maximized. drive a focusing device of a lens, detect and arithmetic process at least one of an aperture value or a focal length value of the lens, and determine a detection band of at least one of the frequency components to be detected according to the arithmetic process. It is an automatic focusing device that changes the lens aperture and focal length.

By changing at least one band to be detected among the frequency components that are processed and detected according to the calculation processing, the response can be improved by suppressing changes in the slope of the chevron-shaped characteristic of the frequency components due to changes in aperture or focal length. It is something that can be kept constant.

DESCRIPTION OF EMBODIMENTS FIG. 3 shows a block diagram of an automatic focusing device in a first embodiment of the present invention.

13 is a high frequency component detection circuit (1) composed of a band pass filter having the same center frequency as in FIG.
Reference numeral 4 denotes a high frequency component detection circuit (It) composed of a band pass filter having a higher center frequency than the high frequency component detection circuit (1) 13, for example, the center frequency 2 [MH
2,]. Reference numeral 16 denotes an arithmetic processing circuit that arithmetic processes the output signals of the high frequency component detection circuits (1) 131 (■) 14 using the output of the arithmetic processing circuit 18, and selects and outputs one of them, for example. A focal length detector 16 detects the focal length of the lens 1, and detects, for example, the position of a zoom device that changes the focal length of the lens 1, and outputs a signal corresponding to the current focal length. Reference numeral 17 denotes an aperture value detector for detecting the aperture value of the lens 1, and outputs a signal corresponding to the current aperture value. Reference numeral 18 denotes an arithmetic processing circuit that processes and outputs each detected value. For example, when the focal length value is less than a predetermined value or the aperture value is more than a predetermined value, the output of the arithmetic processing circuit 16 becomes a high frequency Component detection circuit (II
) 14.

The operation of the automatic focusing device of this embodiment configured as described above will be described below.

The high frequency components detected from the output signal of the image sensor 2 are as follows:
The higher the center frequency of the detected band is, the steeper the slope of the mountain-shaped characteristic becomes. Now, high frequency component detection circuit (1) 1
The output of lens 3 is reduced by the aperture of lens 1, and the slope of the mountain is as shown in Figure 2 (
When the curve gradually changes from 1) to (■), the output of the high frequency component detection circuit (II) 14 will show a slope as shown in Figure 2 (1) because its center frequency is high. Become. On the other hand, when the aperture is open, the output of the high frequency component detection circuit (11) 14 has a steep slope, and even if the lens focusing device deviates slightly from the in-focus position, the amplitude of the output of the high frequency component detection circuit (11) 14 will be too steep. The operating range becomes too narrow due to noise.

Therefore, when the aperture is open, the output of the high frequency component detection circuit (1) 13 is used for focusing operation, and when the aperture is closed, the output of the high frequency component detection circuit (It) 14 is used for focusing operation. In other words, the loop gain or response of the system is approximately constant with respect to changes in aperture over the same operating range. A similar operation is performed with respect to the focal length, making the response of the system constant.

As described above, according to this embodiment, the focal length value and aperture value of the lens are detected, and by increasing the center frequency of the high frequency component detected according to the above-mentioned state, the system loops depending on the focal length and aperture value. without any change in gain.
An autofocusing device with the same response can be realized.

Note that the present invention periodically and optically focuses the subject image formed on the light-receiving surface of the image sensor, detects the amount of blur, and detects the high frequency included in the output of the image sensor based on the detection signal. The lens focusing device is driven so that the amplitude of the high frequency component of the output signal of the image sensor is maximized. It can also be applied to systems that drive For example, even with a method that simply searches the focusing device of the lens, detects changes in the high frequency component due to the movement of the focusing device, detects the position where the amplitude of the high frequency component is maximum, and then stops, the aperture However, if the present invention is implemented, the band of high frequency components to be detected will change, and the slope of the mountain will become constant. The above deterioration can be improved and it works effectively.

In addition, in the first embodiment, the number of bands of high frequency components that can be changed with respect to the aperture value and focal length value is shown as two, but there is no need to be restricted to this. The loop gain becomes more constant with respect to changes in aperture and focal length.

In other words, the present invention detects a plurality of frequency components in different bands from a signal obtained from an image sensor, performs arithmetic processing on the detected frequency components, and adjusts the lens so that the amplitude of the processed output signal is maximized. It can also be applied to a system that drives a focus matching device, and in this case it works effectively by changing at least one band among the plurality of bands by changing the aperture or focal length.

Further, in the first embodiment, the arithmetic processing circuit 16 is configured to select one of the high frequency component detection circuits (1) 1-3 and (II) 14, but there is no need to be restricted to this. Alternatively, for example, the center frequency may be changed by adding two outputs. Furthermore, if the center frequency of the high frequency component to be detected changes, the configuration shown in the embodiment is not restricted in any way; for example, the characteristics can be changed by using a voltage variable capacitance element in the bandpass filter that constitutes the high frequency component detection circuit. You can make it into something.

Further, although the first embodiment has been described in which both the focal length value and the aperture value of the lens are detected, it goes without saying that it is also possible to detect only one of them and perform arithmetic processing.

Furthermore, the configuration of the arithmetic processing circuit 1 is not restricted to the first embodiment.

Effects of the Invention The automatic focusing device of the present invention detects frequency components having one or more different bands from a signal obtained from an image sensor on which a subject image is formed on the light receiving surface, and detects frequency components having one or more different bands. drive the focusing device of the lens so that the aperture value and the focal length value of the lens are at the maximum, detect and calculate at least one of the aperture value and the focal length value of the lens, and at least one of the detected frequency components according to the calculation process. By changing the detection band, the system response can be made to remain the same even when the lens aperture or focal length changes, which has a great practical effect.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a conventional automatic focusing device. Fig. 2 is a characteristic diagram for explaining the principle of detecting the driving direction of a motor. Fig. 3 is a block diagram of an automatic focusing device in a first practical example of the present invention. The block diagram is 1...lens, 2...
...Image sensor, end...High frequency component detection circuit, 9...Reference frequency component detection circuit, 1Q...
... Synchronous detection circuit, 13 ... High frequency component detection circuit (1), 14 ... High frequency component detection circuit (n), 16 ...・Arithmetic processing circuit, 16
. . . Focal length rigidity detector, 17 . . . Aperture value detector, 18 . . . Arithmetic processing circuit. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure □

Claims (1)

[Claims] A lens focusing device that detects frequency components having one or more different bands from a signal obtained from an image sensor on which a subject image is formed on a light receiving surface, and adjusts the frequency components so that the amplitude of the frequency components is maximized. , detects and arithmetic processes at least one of an aperture value and a focal length value of the lens, and changes a detection band of at least one of the detected frequency components in accordance with the arithmetic process. automatic focusing device.