JPH04369184A - Still video camera - Google Patents

Abstract

PURPOSE:To realize the still video camera provided with an automatic focus mechanism by which an image with excellent balance in the focusing state is picked up with simple configuration. CONSTITUTION:In the case of the automatic focusing, after an iris means 14 is opened up to a prescribed aperture, focus adjustment means 31, 32 are activated to allow the automatic focusing to be implemented at a shallow depth of field.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a still video camera, and more particularly to a still video camera equipped with an autofocus mechanism.

0002

2. Description of the Related Art Conventionally, various so-called still video cameras have been developed that record still images as electrical video signals on magnetic disks. In this still video camera, it is necessary to adjust the focus by moving the focus ring of the photographing lens, etc., like a still camera using a normal silver halide film. In this case, some cameras have an autofocus mechanism that allows automatic focus adjustment. Conventionally, in the case of a still camera, the autofocus mechanism detects the distance from the camera to the subject by some method, and moves the focus ring of the photographic lens in accordance with this distance information.

On the other hand, some video cameras for recording moving images detect focus information for autofocus control from the imaging signal itself and perform autofocus control without detecting distance (
(See Japanese Patent Application Laid-Open No. 57-208520, etc.). That is, when the focus adjustment of the lens is appropriate, the outline of the subject can be photographed clearly, so the image signal contains high frequency components. On the other hand, if the focus adjustment of the lens is not appropriate, the outline of the subject will be blurred and the image signal will not contain high-frequency components. Therefore,
By detecting the amount of high-frequency components in the imaging signal, it is possible to detect whether the current focus adjustment state is appropriate, and autofocus control is performed.

[0004]The above-mentioned still video camera also uses a solid-state imaging device to obtain an electrical imaging signal like a normal video camera, so it is necessary to use this imaging signal itself for autofocus control. A method of detecting focus information can be applied. By applying this autofocus method to electronic still cameras, there is no need to detect the distance from the camera to the subject, and the autofocus mechanism can be configured more easily than in still cameras that use silver halide film.

[0005]

By the way, there is a range of focus positions of a lens that can focus on a certain subject. That is, for example, when focusing on a subject at a distance of 4 m from the camera, it may be possible to focus on this subject by setting the focus ring within the range of 3 m to 5 m under certain shooting conditions. Such a focusing range is called the depth of field of the lens. This depth of field changes depending on the aperture amount of the lens, and in the case of a zoom lens, it also changes depending on the focal length.

[0006] When performing autofocus control of a camera by detecting focus information for autofocus control from the imaging signal itself, the target subject can be photographed at any position within the focusing range. Since the image is photographed in a focused state, it is determined that the current focus adjustment state is appropriate. Therefore, it is inconvenient that it is impossible to determine where within the focusing range the subject is in focus, and depending on the shooting conditions, the focus of the shot image may become unnatural. In other words, when focusing at approximately the center of the focusing range, objects in front and behind the target subject (distances from the camera are the same),
Good shots are taken, but for example, when the target subject is focused at the shortest distance within the focusing range, objects closer to the subject are almost always in focus. On the other hand, objects that are further away than the subject will be photographed largely out of focus, resulting in an unbalanced in-focus state.

[0007] In the case of videos shot with a normal video camera, once the target subject is in focus, the focus status of objects in front and behind the subject does not matter much, but with a still camera, When taking a still image, the degree of blurring of objects in front and behind the target subject is an important factor in determining the quality of the photograph.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, it is an object of the present invention to provide a still video camera of this type that has a simple configuration and is capable of photographing well-balanced images in focus.

[0009]

[Means for Solving the Problems] As shown in FIG. 1, for example, the present invention includes an image sensor 21, an aperture means 14 for controlling the amount of imaged light incident on the image sensor 21,
A focusing lens 13 whose movement is controlled so that the imaged light enters the image sensor 21 in a focused state, an electronic viewfinder 27 that displays a video signal obtained from the image sensor 21, and an autofocus start signal A focus adjustment means 31 that, when supplied, drives the focusing lens 13 based on the video signal obtained from the image sensor 21 to perform focus adjustment.
, 32, when the autofocus start signal is supplied, after opening the aperture means 14 to a predetermined position, the focus adjusting means 31,
32 is provided with a control means 30 for controlling the operation thereof.

0010

[Effect] By doing this, when autofocus adjustment is performed, the aperture means opens to a predetermined position and the depth of field becomes shallow, and autofocus is adjusted in this shallow depth of field state. will be held. Then, during actual shooting, when the aperture of the aperture device returns to its original value and the depth of field becomes deeper, the in-focus range expands almost equally from front to back, so the subject is focused approximately at the center of the in-focus range. The focus becomes more focused, and the balance in focus improves.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the accompanying drawings.

In FIG. 1, reference numeral 10 indicates the entire photographing lens, and this photographing lens 10 includes a fixed front lens 1.
1, a zoom lens 12 that adjusts the focal length (i.e., adjusts the angle of view), and a master lens 13 that adjusts the focus (i.e., adjusts the focus).
The lens device is configured as an inner focus type lens device in which the lens is located closest to the image forming surface. In this case, master lens 1
An aperture 14 and a shutter 15 are arranged on the subject side of No. 3, and the aperture 14 can limit the amount of light passing through the master lens 13, and the shutter 15 can control the timing at which image light passes through the master lens 13. .

[0013] The image light that has passed through the photographing lens 10 is then transferred to a solid-state image sensor (hereinafter referred to as a CCD imager).
The image is formed on a phase plate 21, and converted into an electrical imaging signal by this CCD imager 21. In this case, the CCD imager 21 outputs an imaging signal in synchronization with a readout pulse supplied from a pulse generation circuit 28, which will be described later, and the light reception time is controlled by the pulse supplied from the pulse generation circuit 28. This control of the light reception time constitutes a so-called electronic shutter. Then, the imaging signal outputted by the CCD imager 21 is subjected to gain adjustment by a gain adjustment amplifier (not shown) in the imaging signal processing circuit 22, and is converted into a video signal of a predetermined format, and this video signal is sent to the recording circuit 22.
Supply to 3. After the recording circuit 23 performs recording processing, a video signal for recording is supplied to the magnetic head 24 disposed close to the magnetic disk 25, and the magnetic disk 25 is recorded with one field or one frame of still image signals. Record the video signal of the image.

Further, the video signal outputted from the imaging signal processing circuit 22 is supplied to a drive circuit 26 for a liquid crystal display, and the video is displayed on a liquid crystal display 27 under the control of this drive circuit 26. This liquid crystal display 27 is installed in the camera as an electronic viewfinder.

Further, 30 in the figure shows a central control unit (CPU) that controls photography with this camera, and is composed of a one-chip microcomputer, and the image taken by this central control unit 30 is in focus. It is made so that you can judge whether it is or not. That is, the imaging signal obtained by the imaging signal processing circuit 22 is supplied to the bandpass filter 41, the bandpass filter 41 extracts the high-frequency component necessary for determining the in-focus state, and the extracted high-frequency component is detected. The detection circuit 42 detects only the data within the focus area in one screen, and supplies the detected data to the central control unit 30. Then, the central control device 30 determines whether or not the camera is in focus based on this detected data. That is, the focus is adjusted so that the number of detected high frequency components is the largest, and the state where the highest number of high frequency components are detected is determined to be the in-focus state.

Further, the image signal obtained by the image signal processing circuit 22 is supplied to a detection circuit 43, which detects the average brightness level in one screen, and sends this detection data to the central control unit 30. supply to. The central control device 30 determines the exposure state by adjusting the aperture 14 and the like based on the detection data.

Then, the central control unit 30 determines the data of the high frequency component of the supplied imaging signal, and performs focus adjustment so that the high frequency component is maximized. That is, the central controller 30 is configured to be able to control the motor 32 that moves the master lens 13 via the drive circuit 31, so that when performing automatic focus adjustment, the high frequency component is maximized. The master lens 13 is moved by a motor 32. In this case, in this example, this automatic focus adjustment is performed when the release switch 38, which instructs to start photographing, is in a half-pressed state. This release switch 38 is connected to the central control device 30, and is designed to be able to distinguish between two stages of operation: a half-pressed state (first stage) and a fully pressed state (second stage). , when fully pressed, the central controller 30 controls each circuit to take a picture (that is, record on the magnetic disk 25).

Note that when the master lens 13 driven by the motor 32 is at a predetermined focus position (for example, a focus position at infinity), the master lens position detection circuit 37 detects this and sends the detected data to the central control unit. 3
It is designed to be supplied to 0. The central controller 30 can always determine the current position (focus position) of the master lens 13 based on the amount of lens drive by the motor 32 from this predetermined position (the number of steps if the motor 32 is a stepping motor). be.

Furthermore, the central control device 30 is configured to control the light reception time (ie, shutter speed) of the CCD imager 21. That is, the CCD imager 21
The central control unit 30 can control the pulse generation state of the pulse generation circuit 28 that supplies readout pulses, and this control can control the light reception time corresponding to the shutter speed called an electronic shutter.

Furthermore, the central control device 30 is configured to control the aperture 14 and shutter 15 attached to the photographing lens 10. That is, the central controller 30 controls the motor 3 that drives the aperture 14 via the drive circuit 33.
4, and a motor 36 for opening and closing the shutter 15 can be controlled via a drive circuit 35. In this case, the aperture 14 of this example
When the release switch 38 is pressed halfway and an instruction is given to perform automatic focus adjustment, the central control unit 30 controls the camera so that it is temporarily opened; The amount of aperture is set according to the average brightness level detected by the detection circuit 43.

Further, the shutter 15 of this example is controlled to be in an open state during normal times, and is controlled to be in a temporarily closed state only immediately after photographing. That is, when the release switch 38 is fully pressed to perform photography, the central controller 30 first controls the pulse output state of the pulse generation circuit 28 to sweep away the signal charge accumulated in each pixel of the CCD imager 21. When the signal charge is accumulated for an appropriate time corresponding to the shutter speed, shutter 1 is activated.
Close 5. Then, the signal charge accumulated at this time is read out as an imaging signal, and when the readout is completed,
The shutter 15 is opened again under the control of the central controller 30. Note that the shutter that operates in this manner was previously proposed by the applicant of the present invention, as shown in Japanese Patent Application Laid-Open No. 117775/1983.

Next, the operation when taking pictures with the still video camera of this example is shown in FIG. 2, focusing on focus control.
This will be explained with reference to the flowchart.

First, when photographing with the still video camera of this example, before actually photographing, press the release switch 38 halfway to perform automatic focus adjustment, and check the focus adjustment state on the liquid crystal display 27. It is necessary to confirm. Therefore, as shown in the flowchart of FIG. 2, the central controller 30 determines whether or not the release switch 38 is in the half-pressed state (step 101), and only when the release switch 38 is in the half-pressed state, the next step is to perform focus adjustment. Move to. Then, when the button is pressed halfway and the process moves to the next step 102, the diaphragm 14 is first opened. At this time, the light intensity is adjusted using an electronic shutter that controls the light reception time of the CCD imager 21, and when the electronic shutter alone cannot sufficiently adjust the light intensity (i.e., the light intensity cannot be narrowed down sufficiently even with the fastest shutter speed). case), the gain of the gain adjustment amplifier in the imaging signal processing circuit 22 is lowered and adjusted (step 103). Note that this light intensity adjustment is performed by the central controller 30 using the detection circuit 43.
This is done by determining the amount of light to be photographed based on the detected data.

Then, in this state, the master lens 13 is moved under the control of the central controller 30 so that the high frequency component in the image signal becomes the largest, and automatic focus adjustment is performed (step 104). When this automatic focus adjustment is completed, the light amount adjustment based on the shutter speed of the electronic shutter and the gain of the gain adjustment amplifier is canceled (step 105), and the light amount adjustment using the aperture 14 is restarted (step 106). In this state, the person performing the photographing operation checks the focus adjustment state of the photographed image displayed on the liquid crystal display 27, and when the focus adjustment state is determined to be good, the person performing the photographing operation presses the release switch 38.
Press to the second step (that is, press completely) to execute photography. Then, when the central controller 30 determines that the release switch 38 has been completely pressed (step 10
7) At this time, the video signal based on the output of the CCD imager 21 is transferred to the magnetic disk 25 in one field or one
The frame is recorded (step 108), and the photographing operation is ended.

By performing automatic focus adjustment before photographing in this way, when focus adjustment is actually being performed, the diaphragm 14 attached to the photographic lens 10 is in an open state, and the depth of field is improved. is the shallowest state (that is, the in-focus range is the narrowest state). and,
If you accurately focus on the subject at this time, when actually shooting, the aperture 14 will be closed down from its open state, deepening the depth of field and expanding the in-focus range, but the in-focus range will be approximately Since it spreads evenly, the subject will be in focus approximately at the center of the focusing range. In this way, by focusing on the subject at approximately the center of the focusing range, objects in front and behind the subject will be approximately the same out of focus, and an image with a well-balanced focus state will be captured.

Furthermore, when the depth of field is at its shallowest, high-frequency components in the image signal can be detected well, and automatic focus adjustment can be performed quickly and with high precision. That is, when the in-focus range is the narrowest, the master lens 13
The high-frequency components in the imaging signal change greatly as the image moves, and the focus position with the most high-frequency components is easily determined.
The time required for focus adjustment is shortened, and the accuracy of autofocus adjustment is also increased.

[0027] When photographing at night or in a dark room, it is possible that the diaphragm 14 may remain open and remain unchanged even when switching to adjusting the amount of light using the diaphragm 14 during photography. Photographing is rarely performed, and even if the lens is left in the open state, the in-focus state is maintained, so there is no problem in photographing.

In the above-described embodiment, the diaphragm 14 is set to the open state when adjusting the focus, but the focus may be automatically adjusted after the diaphragm 14 is slightly stopped from the open state. Furthermore, it goes without saying that the present invention is not limited to the above-mentioned embodiments, and can take various other configurations.

[0029]

According to the present invention, when autofocus adjustment is performed, the autofocus adjustment is performed in a state where the depth of field is shallow, and highly accurate autofocus adjustment is performed in a short time. The subject will now be in focus at approximately the center of the focusing range, resulting in still images with well-balanced focus conditions.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention.

FIG. 2 is a flowchart diagram for explaining one embodiment.

[Explanation of symbols]

10 Photography lens 13 Master lens 14 Aperture 15 Shutter 21 CCD imager 22 Imaging signal processing circuit 25 Magnetic disk 27 Liquid crystal display 30 Central control unit 31, 33, 35 Drive circuit 32, 34, 36 motor 38 Release switch 41 Bandpass filter 42, 43 Detection circuit

Claims (1)

[Claims] 1. An image sensor, an aperture means for controlling the amount of imaged light incident on the image sensor, and a movement controlled so that the imaged light is incident on the image sensor in a focused state. an electronic viewfinder that displays a video signal obtained from the image sensor; and an electronic viewfinder that displays a video signal obtained from the image sensor when an autofocus start signal is supplied, and a focusing lens that displays the image signal obtained from the image sensor when an autofocus start signal is supplied. In the still video camera, the diaphragm means is opened to a predetermined position when the autofocus start signal is supplied, and then the aperture means is opened to a predetermined position.
A still video camera comprising a control means for controlling the operation of the focus adjustment means.