JPH06133204A - Automatic focus adjustment device - Google Patents

Abstract

PURPOSE:To attain focusing with high precision quickly even under the image pickup condition where a depth of object field is very deep such as use of a lens with a short focal distance or an object with high brightness. CONSTITUTION:A CPU 17 obtains photometry data from a photometry circuit 4, decides shutter speed by an AF exclusive use program line so as to set a diaphragm in the vicinity of the open aperture and controls a CCD 3 to obtain the decided shutter speed. An AE control circuit 12 controls the diaphragm to obtain a proper exposure at the decided shutter speed. The AF control is implemented in this state and the AE use program line is selected and the shutter speed and the diaphragm are set again.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an autofocus device used for a camera for recording a still image of a video signal such as an electronic still camera, more specifically, a focusing speed under a shooting condition where the depth of field is deep. And an automatic focusing device with improved accuracy.

[0002]

2. Description of the Related Art One of the autofocus devices used in video cameras and the like is the "mountain climbing servo system" announced by NHK Giken. This is for extracting a high-frequency component in a video signal and detecting the in-focus point based on the extracted high-frequency component, which is widely used in current video cameras and the like. This method does not require a sensor dedicated to AF and is advantageous in terms of cost and mounting.

FIG. 4 is a block diagram showing an outline of a circuit of a video camera or the like which adopts the hill climbing servo system. Reflected light from a subject (not shown) is converged by the lens unit 1, narrowed down by the iris 2 and reaches the CCD 3 to form an image. The CCD 3 performs photoelectric conversion and sends an electric signal to the camera process circuit 5. Camera process circuit 5
Creates a video signal by adding a sync signal and setup level. The video signal is sent to another circuit such as a recording circuit (not shown), and a part of the luminance signal is sent to the high pass filter 6 and the AE control circuit 12. A high frequency component is extracted from the luminance signal sent to the high pass filter 6. The high frequency component is amplified by the amplifier 7 and then converted into a digital signal by the A / D converter 8.

The gate circuit 11 outputs a horizontal synchronizing signal HD and a vertical synchronizing signal VD output from the camera process circuit 5.
Based on the above, a gate control signal for controlling the range-finding frame range to be integrated is output. The arithmetic logic unit 9 is a gate circuit 1
The digital signal from the A / D converter 8 is integrated based on the gate control signal from 1. The CPU 10 compares the integrated data output from the arithmetic logic operation unit 9 in time series, and sends a control signal for driving the lens unit to the lens motor drive circuit 15 in a direction in which the output of the arithmetic logic operation unit 9 increases. . The lens motor drive circuit 15 is CP
The lens motor 16 is driven in the direction according to the instruction from U10 to move the position of the focus adjustment lens in the lens unit. By continuously comparing the integrated data and continuously driving the lens, the focus adjustment lens is moved in the direction in which the high frequency component becomes maximum, and finally reaches the maximum value of the high frequency component, that is, the in-focus point. On the other hand, the AE control circuit 12
Sends a control signal to the iris motor drive circuit 13 based on the brightness signal, which should be a diaphragm for proper exposure for a fixed shutter speed. The iris motor drive circuit 13 drives the iris 2 according to the control signal from the AE control circuit 12 to set the proper exposure.

[0005]

In the above focusing method, the fixed shutter speed is 1/60 sec, and a video camera generally shoots at this shutter speed. Therefore, when a lens with a short focal length is used or when the brightness of the subject is high, the depth of field becomes very deep, and it is difficult to detect the in-focus position. It has a drawback that it takes time and cannot focus accurately. The electronic still camera is required to have a short focusing time because it requires high-speed shooting. Further, since it is a still image recording / reproduction, high focusing accuracy is required, and the above focusing method is unsuitable. As a countermeasure, it is conceivable to provide a photometric sensor like the silver halide camera and control the shutter speed and the iris to set the exposure based on the photometric value, but the above problems may not be avoided. SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems, and to provide an automatic focus adjusting device that can perform focusing quickly and with high accuracy even under shooting conditions in which the depth of field is extremely deep.

[0006]

In order to achieve the above object, an automatic focusing apparatus according to the present invention converts a subject image formed on a solid-state image pickup device through a lens system into a video signal, and selects from among the video signals. In an autofocus device for focusing on the basis of the extracted high frequency component, a memory for storing a photometric circuit for obtaining a photometric value, an AF-only program in which the aperture value is set near the open end, and an AE program. And a control means for performing AF control on the program line dedicated to the AF based on the photometric value and then performing AE control by the program line for AE.

[0007]

According to the above construction, the aperture is set close to the full aperture during the AF control even when the depth of field is deep.
Since the shutter speed and the aperture value are set again by the AE program later, focusing can be performed quickly and with high accuracy. Therefore, it can be suitably used for an autofocus device of an electronic still camera.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in more detail below with reference to the drawings. FIG. 1 is a circuit block diagram showing an embodiment of an automatic focusing apparatus according to the present invention. Portions with the same reference numerals as the respective circuit portions in FIG. 4 are circuit configuration portions that function in the same manner. In FIG. 1, a photometric circuit 4 for directly measuring external light is provided, and its data is input to the CPU 17. The CPU 17 has a storage unit for storing the AF dedicated program and the AE program, and initially controls the shutter speed and the aperture value by the AF dedicated program, and simultaneously performs the AF control. Then, when the AF control is finished, the next step is A
The shutter speed and aperture value are set again by the E program, and shooting is possible.

FIG. 2 is a diagram showing examples of the AF dedicated program and the AE program. In the AF dedicated program A, the shutter speed is set so as to be close to the aperture opening. On the other hand, the AE program B is set to a normal proper aperture and proper shutter speed. For example, when the EV value is 12, the aperture is usually 8 to 5.6, and the shutter speed is 1/60 second to
The AF control is performed by setting it to 1/125 seconds, but in the present invention, first, in the vicinity of the aperture of 2.0, the shutter speed is 1/1000.
Second to 1/2000 second, that is, after the AF control is performed with the aperture value slightly open, the normal AE control is performed.

FIG. 3 is a flow chart showing a control sequence at the time of photographing. The operation of FIG. 1 will be described in detail below along this flow. When a release button (not shown) is pressed halfway, AF and AE control is performed. The CPU 17 obtains photometric data from the photometric circuit 4 (step "hereinafter, ST
1), the shutter speed is determined based on the AF-dedicated program line, and the CCD 3 is controlled so that the determined shutter speed is achieved. The AE control circuit 12 controls the iris motor drive circuit 13 based on the brightness signal under the shutter speed to set the aperture value to the proper exposure value (ST2).

Under the AE control as described above, the CPU 17 compares the integrated values of the high frequency components in the distance measuring frame gated by the gate circuit 11 and moves the lens in the direction in which the integrated value increases. A power control signal is sent to the lens motor drive circuit 15. The lens motor drive circuit 15 drives the lens motor 16 based on the control signal to move the lens. By repeating this operation, the lens is driven so that the integrated value becomes the maximum value, and the in-focus point is obtained (ST3). When the AF control is completed, the CPU 17 then switches to the AE program line, determines the shutter speed based on this AE program line, and controls the CCD 3 so that the determined shutter speed is reached. The AE control circuit 12 controls the iris motor drive circuit 13 based on the brightness signal under the shutter speed to reset the aperture value (ST4).

[0012]

As described above, according to the present invention, the AF control is first performed under the AF-dedicated program line that is close to the aperture opening, and then the shutter speed and the aperture are reset by the AE program line. Is configured. When the depth of field is deep, the high-frequency component in the video signal can be sufficiently detected, but the change due to the lens driving becomes small, so that it becomes difficult to determine the focus point. Therefore, it is difficult to perform AF photography with a deep depth of field using a lens having a short focal length, but according to the present invention, high-performance AF control can be performed without damaging the depth of field in image creation. become. In addition, when the subject has high brightness, for example, backlight,
As a result of the diaphragm being narrowed, a focus signal is less likely to be output, but in such a case, high-speed and highly accurate AF control can be performed.

[Brief description of drawings]

FIG. 1 is a circuit block diagram showing an embodiment of an automatic focusing device according to the present invention.

FIG. 2 is a diagram showing an example of an AF dedicated program and an AE program.

FIG. 3 is a flowchart for explaining a control sequence at the time of shooting.

FIG. 4 is a circuit block diagram showing an example of a conventional autofocus device.

[Explanation of symbols]

 1 Lens Unit 2 Iris 3 CCD 4 Photometric Circuit 5 Camera Process Circuit 6 HPF 7 AMP 8 A / D Converter 9 Arithmetic Logic Operator 10, 17 CPU 11 Gate Circuit 12 AE Control Circuit 13 Iris Motor Drive Circuit 14 Iris Motor 15 Lens Motor drive circuit 16 Lens motor

Continuation of front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location G03B 7/091 9224-2K H04N 5/238 Z

Claims (1)

[Claims] 1. An autofocus device for converting a subject image formed on a solid-state image sensor through a lens system into a video signal, and focusing based on a high frequency component extracted from the video signal. A photometric circuit for obtaining the value, a storage unit that stores an AF-dedicated program in which the aperture value is set close to the opening, and an AE program, and AF control is performed on the AF-dedicated program line based on the photometric value. Then, the automatic focus adjusting device is provided with a control means for performing AE control by the program line for AE thereafter.