JP2008111897A - Autofocus device and imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an autofocus device capable of quickly bringing a desired subject into focus. <P>SOLUTION: The autofocus device includes: a measuring means for measuring information corresponding to a subject distance; a focus signal generation means for generating a focus signal corresponding to the contrast of an image based on a signal from an imaging means; and a focus control means for acquiring a focused position as a moving target for a focus lens by driving and controlling the focus lens in an optical axis direction based on the focus signal. The focus control means eliminates the focused position (L) corresponding to the subject distance based on information obtained by the measuring means from the focused position by the focus control means. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an autofocus device having a focus control means for driving and controlling a focus lens in an optical axis direction based on a focus signal corresponding to a contrast of an image, and acquiring a focus position as a movement target of the focus lens; The present invention relates to an imaging device.

  When using a camera, skilled camera work technology is required to photograph a subject while manually adjusting the focus. Thus, an autofocus device that automatically focuses is developed so that even an amateur can always take a focused image, and has been mounted on an imaging device such as a camera or a video camera.

  An autofocus device in a conventional imaging device will be described. One or more areas in the center of the angle of view is set as a distance measurement area (including the focus detection area), and high frequency components are extracted from the video signals imaged in the distance measurement area. Thus, the magnitude of the high frequency component is defined as the sharpness of the image. In general, the focus lens is driven while evaluating the sharpness, and the position of the focus lens is controlled so that the sharpness is maximized, thereby performing automatic focusing.

  In addition, two systems are used as a sequence for automatic focusing, for moving image and still image shooting. It is a method adopted as a case where a focused state is always desired as in moving image shooting, and a method adopted as a case where it is sufficient to focus at the moment when the shutter is released as in still image shooting. In the case of moving images, it is necessary to always focus, so the sharpness near the current lens position is evaluated and the focus lens is driven to a position higher than the current focus signal (AF evaluation value). The method to do is adopted. In the case of still image shooting, a scan method is used in which the AF evaluation value is calculated over the entire driving range of the focus lens when the release shutter is half-pressed, and the focus lens is driven and fixed at a position with the highest sharpness. .

  In cameras equipped with these autofocus devices, in many cases, a distance measuring area is shown in the viewfinder, and a target subject is adjusted to this distance measuring area. Therefore, it is easy to focus the target subject by moving the angle of view of the subject lined up horizontally. However, when the subject is lined up in the optical axis direction, the angle of view cannot be moved to the front or back, so it is not easy to select and focus the subject.

  In this way, if the subject is aligned in the optical axis direction of the camera and an object different from the target subject is focused, the angle of view is reduced using zoom to focus on the target object. Try to do so. Or it was necessary to switch the autofocus to the manual focus mode and adjust the focus manually.

In view of this point, Patent Document 1 proposes that an auxiliary operation of autofocus can be performed using a manual focus ring as means for changing the focus position without changing the angle of view for photographing.
Japanese Patent Laid-Open No. 06-197256

  However, in the above-mentioned Patent Document 1, the operation is the same as manual focus, in which the ring is rotated and adjusted, and for this purpose, an operation such as changing the camera is required. In addition, after moving the focus from the subject different from the target to the target subject, if the camera work is performed or the operation of rotating the ring is performed, the focus returns to the subject to be focused again. It was very likely.

(Object of invention)
An object of the present invention is to provide an autofocus device and an imaging device that can quickly focus on a desired subject.

  In order to achieve the above object, the present invention includes a measurement unit that measures information corresponding to a subject distance, a focus signal generation unit that generates a focus signal corresponding to an image contrast based on a signal from an imaging unit, Focus control means for driving and controlling the focus lens in the optical axis direction based on the focus signal to obtain a focus position as a movement target of the focus lens, and the focus control means at the measurement means In this embodiment, the focus position corresponding to the subject distance based on the obtained information is excluded from the focus position by the focus control means.

  Similarly, in order to achieve the above object, the present invention is an imaging apparatus having the autofocus device of the present invention.

  According to the present invention, it is possible to provide an autofocus device or an imaging device that can quickly focus on a desired subject.

  The best mode for carrying out the present invention is as shown in the following examples.

  FIG. 1 is a system configuration diagram showing an outline of a video camera according to an embodiment of the present invention. In FIG. 1, a lens unit 100 surrounded by a dotted line includes a fixed lens 101, a zoom lens 102, a diaphragm blade 103 for adjusting the amount of light, a fixed lens 104, a focus lens 105, and a position encoder 108. Further, a zoom lens driving motor 106 and a focus lens driving motor 107 are provided. The position encoder 108 functions as means for detecting the positions of the zoom lens 102, the diaphragm blade 103, and the focus lens 105.

  Each part of the video camera on which the lens unit 100 is mounted is connected via a bus 122 and has a structure controlled by the main CPU 110. When the recording mode is activated by a switch included in the operation switch group 115, the program stored in the flash memory 113 is loaded into a part of the RAM 112. The main CPU 110 operates according to the program loaded in the RAM 112.

  Light from the subject passes through a lens group in the lens unit 100 and forms an image on an image sensor 109 such as a CCD. The imaging element 109 may be a three-plate imaging system provided for each of the three primary colors red, green, and blue. This image sensor 109 performs photoelectric conversion, and the image signal processor 119 amplifies the signal to an optimum level, or in the case of a three-plate type, adds three image sensor outputs and converts it to one video signal. Or Then, signal processing such as conversion to a predetermined image / video format is performed. Thereafter, the image is output to the monitor display 114 as a video, or the video is recorded on the image recording medium 116.

  On the other hand, light from the subject passes through the fixed lens 130 and forms an image on the line sensor 131. The line sensor 131 has two line sensors A and B arranged in parallel across the center of the fixed lens 130. The phase difference between these outputs is detected, and the distance to the subject is measured. The Based on this distance, the focus control unit 121 drives the focus lens 105 via the focus lens drive motor 107. That is, focus control based on distance information (hereinafter referred to as first focus control) is performed.

  On the other hand, a high-frequency component is extracted from the imaging signal through a band-pass filter or the like, and passed to the focus control unit 121 as a focus signal (AF evaluation value) corresponding to the contrast of the image. Then, based on the AF evaluation value, the focus control unit 121 drives the focus lens 105 via the focus lens drive motor 107. By repeating this series of cycles, focus control (hereinafter, second focus control) is performed.

  As shown in FIG. 2, in the first focus control and the second focus control, the first focus control (outside focus) is detected quickly when the highly accurate second focus control (TVAF) is in the out-of-focus state. A predetermined use is performed such that measurement is used. In this manner, the focus speed is increased and a highly accurate focus operation is performed.

  FIG. 3 is a flowchart of the schematic operation of the focus control in the case where a mode is set in which the focus is not set on the wire mesh or the fence when there is a wire mesh or the fence in the vicinity using the system described above. It explains using. The mode is, for example, the portrait mode of the program AE.

  In a state where the focus is immediately after the switch is activated, in step S301, the CPU 110 receives the values of the position of the focus lens 105 and the position of the zoom lens 102 obtained from the position encoder 108, and based on the output of the line sensor 131, the subject. Until the distance X is calculated. This distance is measured and calculated as X when there is a wire mesh or a fence in the vicinity. In the next step S302, it is determined whether or not the restriction switch in the operation switch group 115 has been depressed by the user. If not depressed, the process proceeds to step S303, and if depressed, the process proceeds to step S304. In step S303, it is determined whether or not a restriction mode for restricting the in-focus position avoiding the wire mesh or wrinkle by the dial or the like is set by the dial or the like. If the restriction mode is not set, the process proceeds to step S305. If the mode is set, the process proceeds to step S304.

  If the restriction switch is not depressed (NO in step S302) and the restriction mode is not set (NO in step S303), the process proceeds to step S305, where the first focus control increases the distance by the first focus control. The focus lens 105 is driven in the vicinity of X. Thereafter, the process proceeds to step S307, and the process proceeds to the second focus control (TVAF) as it is, and a normal highly accurate AF operation is performed.

  On the other hand, when the restriction switch is pressed down (YES in step S302), or when the mode is set by a wire mesh or a restriction mode that avoids wrinkles (YES in step S303), as described above. Proceed to step S304. In step S304, the focus lens 105 is driven at a high speed to the far side of the distance X by the first focus control. That is, it is assumed that the subject at the distance X is a close subject such as a wire mesh and is not the main subject. In the next step S306, the AF evaluation value for second focus control is lowered by a predetermined range according to the value of the distance X. Thereafter, the process proceeds to step S307, and AF driving is performed by the second focus control.

  In step S306, the width for excluding the in-focus position at the distance X (the AF evaluation value is lowered by a predetermined range) is a limit width L calculated from a predetermined value in the flash memory 113 and the subject distance. It is mapped. Within the limit width L centered on the current subject distance, the AF evaluation value is calculated to be extremely low (restricted so that the AF evaluation value is almost zero or less than a predetermined value with a small inclination). Therefore, the second focus control is controlled based on a conventional AF control algorithm in which the focus lens 105 is driven to a position where the AF evaluation value is high. At this time, in order to make it easier for the user to understand that the AF position is being limited to a subject position within a certain range (limit width L), the numerical value of the subject distance within the limit width L is displayed on the monitor display 114 or a finder (not shown). It is trying to display. An example of the display is a bar display, which may be expressed by changing the color in the bar.

  The above is a schematic description of the present embodiment. This will be described in detail below with reference to FIG.

  FIG. 4A assumes a shooting scene in which a ground is shot over a wire mesh at a baseball stadium, and the horizontal axis indicates the distance X of the subject (in terms of the nature of the focus lens when there is no zoom), vertical It is the figure which took AF evaluation value on the axis | shaft.

  In the order closer to the photographer, the component due to the wire mesh comes out at H1, the batter in the batter BOX at H2, and the maximum point of the AF evaluation value by the pitcher at H3. Under this photographing condition, X1 and X2 are detected as the distance X obtained from the signal from the line sensor 131. When the restriction switch is pushed down by the user or when the restriction mode is set to prohibit focusing, the focus lens 105 is driven from the position A to the position B as shown in FIG. At this time, the value of the limit width L is obtained by a predetermined calculation method. The AF evaluation value of the portion of the limit width L near H1 is calculated to be low, and as a result, it is recognized as an AF evaluation value as shown by the solid line in FIG.

  Therefore, after that, the second focus control function works according to the AF evaluation value. As a result, focusing is performed at the position of H2 where there is an AF evaluation value component by the batter. In other words, focusing on the H2 position can be performed quickly by forcibly driving at high speed without AF in the range of the limit width L (focusing position exclusion range) before entering the AF function.

  Thereafter, when a predetermined reset condition is satisfied, for example, by depressing the switch a predetermined number of times, the low calculated AF evaluation value is reset to return to the original AF evaluation value, the state of FIG. Continue operation with normal AF function. The “predetermined reset condition” that is reset and returns to the original AF evaluation value will be described later.

  Next, the limit width L (see FIG. 4B) forcibly driving at high speed without AF will be described.

  For the limit width L, one or a plurality of setting methods described below are used. The first setting method is to use only one numerical value registered in advance in the camera. The second setting method is a method set by the user. Specifically, the user himself / herself performs the setting by inputting a numerical value using one of the switches. Similar to other camera settings such as the number of recording pixels and AF or MF (manual focus), it may be selected from predetermined large, medium, small, and the like. The third setting method is a method of setting when a plurality of subject distances have a predetermined correlation when a plurality of subject distances are detected.

  The fourth setting method is a setting method based on the depth of field. The depth of field refers to the length (depth) at which the subject is in focus, and the depth of field becomes shallow as the focal length becomes longer, the aperture is opened, or the shooting distance becomes shorter. Therefore, when setting the limit width L, the depth of field is calculated by combining the aperture value from the position of the aperture blade 103 and design values such as the focal length of the lens unit 100. For this reason, the depth of field and the limit width L are created empirically in advance and mounted in the flash memory 113 as shown in FIG. Then, after the depth of field is calculated, the limit width L is set with reference to FIG. Note that the depth of field may be calculated from the aperture value, the focal length, and the design value of the lens unit 100, and may have a calculation formula without having data as shown in FIG. In the third setting method, the limit width L can be determined if the depth of field can be calculated from either one.

  The limit width L is set using the above method. However, since the front depth of field is generally shallower than the rear depth of field, it is desirable that the center of the limit width L that is actually prohibited from focusing is slightly farther and the subject distance is longer. .

  Next, the aforementioned “predetermined reset condition” will be described.

  As described above, the AF evaluation value is limited to a small range within the limit width L by the switch operation by the user. The evaluation value once reduced is maintained unless the “predetermined reset condition” is satisfied, and is maintained so as not to focus on a subject located at a distance within the limit width L. As a cancellation method, the following method is used. Can be mentioned.

  One is based on a user operation such as providing a release-dedicated switch and pressing it down. The other is a method of canceling in response to a change in the shooting environment. For example, when the zoom is changed, when the white balance changes more than a predetermined amount, when the output of vibration detection means (gyro etc.) provided in the camera changes more than a predetermined amount, when the exposure amount changes significantly, or When the focus position exclusion range of the limit width L is approached, it can be determined that the shooting environment has changed. A “reset condition” is designed using one or more of the above conditions.

  FIG. 6 is a diagram in which the focus lens position is plotted on the vertical axis and the zoom lens position is plotted on the horizontal axis, and the locus of the focus lens position is depicted for each subject distance.

  In zoom using a computer, zooming can be performed without defocusing by driving the lens according to this locus. In FIG. 6, the intersections of the curved line when the subject distance is infinite (∞), 5 m, 2 m, and 80 cm and the dotted line with the zoom lens position Z1 are denoted as A1, B1, C1, D1, and the zoom lens position. Each intersection with Z2 is shown as A2, B2, C2, D2.

  If the limit width L as described above is, for example, between 2 m and 80 cm in FIG. 6, the lens positional relationship of the gray portion in FIG. 6 corresponds to the focus position exclusion range. Here, as can be seen from FIG. 6, it is particularly effective at the tele end of the zoom lens 102, and the depth of field may be deep at the wide end, which is difficult, so at the tele end (shallow depth of field). Only the in-focus position is excluded (in-focus is prohibited).

  As described above, since the restriction function is added to the normal AF function, the subject can be quickly changed even when the target subject is not met.

  Specifically, according to the present embodiment, a function of directly measuring the distance of the subject and limiting the focus position of the focus lens 104 with the measured distance X as a reference in a restriction mode or the like is added. As a result, the AF evaluation value is immediately limited in the focus position exclusion range, and an unintended subject is not focused.

  Therefore, it is possible to easily focus on a target subject on the back side (back) of a wire mesh, a fence, etc. while effectively using an accurate AF function (second focus control). In addition, the restriction function is maintained until the condition to be released is satisfied, and the restricted subject distance is maintained, so that the conventional inconvenience of returning to an undesired subject by simple camera work is eliminated. effective.

1 is a system configuration diagram showing an outline of a video camera according to an embodiment of the present invention. It is a figure which shows the division | segmentation of 1st focus control and 2nd focus control concerning one Example of this invention. It is a flowchart which shows operation | movement of the principal part concerning one Example of this invention. It is explanatory drawing about the restriction | limiting of AF evaluation value concerning one Example of this invention. It is a figure which shows the relationship between the depth of field and the restriction width L concerning one Example of this invention. It is a figure which shows the locus | trajectory of the focus position according to to-be-photographed object distance concerning one Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Lens unit 101 Fixed lens 102 Zoom lens 104 Fixed lens 105 Focus lens 106 Zoom lens drive motor 107 Focus lens drive motor 108 Position encoder 109 Image pick-up element 110 CPU
DESCRIPTION OF SYMBOLS 111 Image processing part 113 Flash memory 114 Monitor display 115 Operation switch group 119 Imaging signal processing part 120 Zoom control part 121 Focus control part 130 Fixed lens 131 Line sensor

Claims (8)

Measuring means for measuring information corresponding to the subject distance;
A focus signal generating means for generating a focus signal corresponding to the contrast of the image based on a signal from the imaging means;
Focus control means for driving and controlling the focus lens in the optical axis direction based on the focus signal to obtain a focus position as a movement target of the focus lens;
The autofocus apparatus, wherein the focus control means excludes a focus position corresponding to a subject distance based on information obtained by the measurement means from a focus position by the focus control means.   2. The autofocus device according to claim 1, wherein when the focus position is excluded by the focus control means, the focus lens is moved faster than when the focus lens is not excluded to the far side.   3. The auto according to claim 1, wherein the focus control unit includes a restriction start unit that starts to limit the focus position, and a limit release unit that releases the limit of the focus position. 4. Focus device. Having depth of field detection means for detecting depth of field,
The autofocus device according to any one of claims 1 to 3, wherein the focus control unit determines a range in which a focus position is excluded based on the depth of field.   4. The autofocus device according to claim 3, wherein the restriction start unit functions in a portrait mode of the program AE.   4. The autofocus device according to claim 3, wherein the restriction release unit functions in response to a change in a shooting environment.   The autofocus device according to any one of claims 1 to 6, further comprising display means for displaying the range for excluding a focus position.   An image pickup apparatus comprising the autofocus device according to claim 1.

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