JP5744501B2 - Focus adjustment apparatus, control method thereof, and program - Google Patents

Description

  The present invention relates to a focus adjustment apparatus applicable to autofocus used for electronic still cameras, videos, and the like, a control method thereof, and a program.

  2. Description of the Related Art Conventionally, in an electronic still camera or the like, as a method of moving a focus lens position to focus on a subject, an autofocus (AF) method that automatically performs a focusing operation using an image signal obtained from an image sensor such as a CCD Is used. In addition, there is an AF method in which a frame rate when reading a plurality of AF images from an image sensor is changed according to luminance and shutter speed (see Patent Document 1).

  In addition, there is one that controls the focus lens driving speed in accordance with the shutter speed (see Patent Document 2). Furthermore, in the configuration in which the stepping motor that drives the focus lens is driven with a sine wave, a speed fluctuation pattern is prepared for each phase, the sinusoidal excitation waveform is corrected with the speed fluctuation pattern, and the fluctuation of the focus speed is corrected. (See Patent Document 3).

JP 2003-262788 A Japanese Patent Laid-Open No. 06-098238 Japanese Patent Laid-Open No. 03-139197

  There is a problem that a desired AF scan operation cannot be performed when the set focus lens driving speed cannot be obtained due to the resolution limitation in the motor control for driving the focus lens. For example, when PWM control is performed using a stepping motor in driving the focus lens, depending on the combination of the number of divisions and the operation clock, a focus lens drive speed that cannot be controlled occurs. If the focus lens drive speed cannot be actually obtained even though the predetermined focus lens drive speed is set, a desired number of AF scan points cannot be acquired. In that case, it becomes impossible to detect the focus position of the subject.

  In Patent Document 2, the focus lens drive speed is controlled in accordance with the shutter speed, but no countermeasure is considered when there is a focus lens drive speed that cannot be obtained. In Patent Document 3, in focus lens drive control by a stepping motor, variations in focus speed due to magnetic flux unevenness of each phase are corrected. However, no countermeasure is taken when there is a focus lens drive speed that cannot be obtained.

  The present invention has been made in view of the above points. In the case where the frame rate is made variable according to the shutter speed, the desired AF can be achieved even when the desired focus speed cannot be obtained due to the control of the focus lens drive. The purpose is to ensure the number of scan points.

The focus adjustment apparatus of the present invention obtains a focus evaluation value indicating the contrast of a subject in a predetermined area based on a video output signal obtained via an imaging optical system including a focus lens and an imaging device, and the focus evaluation value is A focus adjusting device that adjusts the position of the focus lens so as to be maximized, and is controlled by the exposure control means that controls the exposure of the shutter speed, aperture, and sensitivity based on the video output signal, and the exposure control means. Frame rate setting means for setting a frame rate according to the shutter speed, drive range setting means for setting a range for driving the focus lens when performing focus adjustment, and the video output signal 1 when performing focus adjustment. A drive amount setting means for setting an amount for driving the focus lens in the frame; and the focus set by the drive amount setting means. Surenzu calculates the driving speed of the focus lens based on the frame rate set by the amount and the frame rate setting means for driving if determines that the driving speed of the focus lens with the calculated put out, focus the calculated A speed setting means for setting a driving speed of the fastest focus lens that can be output below the calculated driving speed of the focus lens when the driving speed of the lens is set and it is determined that the calculated driving speed of the focus lens cannot be obtained; , characterized in that by controlling the motor for driving the focus lens and a control means for driving the focus lens.

  According to the present invention, when the frame rate is made variable according to the shutter speed, it is possible to secure a desired number of AF scan points even when a desired focus speed cannot be obtained due to control of the focus lens drive.

It is a block diagram which shows the structure of the electronic camera which concerns on 1st Embodiment. It is a flowchart showing operation | movement of the electronic camera which concerns on 1st Embodiment. It is a flowchart showing AF operation | movement in 1st Embodiment. FIG. 6 is a characteristic diagram illustrating a relationship between a scan interval, a focus speed, and a frame rate in the first embodiment. It is a figure explaining AF scan operation | movement. It is a flowchart showing AF operation | movement in 2nd Embodiment. 10 is a flowchart illustrating a scan interval / focus speed setting operation according to the second embodiment.

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.
(First embodiment)
FIG. 1 is a block diagram showing a configuration of an electronic camera according to a first embodiment provided with a focus adjusting apparatus to which the present invention is applied. Reference numeral 101 denotes a photographing lens including a zoom mechanism, reference numeral 102 denotes an aperture and a shutter that control the amount of light, and reference numeral 104 denotes a focus lens that focuses on an image sensor 107 described later. The photographing lens 101, the aperture / shutter, and the focus lens 104 constitute a photographing optical system. Reference numeral 103 denotes an automatic exposure (hereinafter referred to as AE) processing unit. Reference numeral 105 denotes a motor that drives the focus lens 104, and a stepping motor that is driven by excitation pulses that are divided in predetermined steps and generated in a substantially sine wave shape is used. Reference numeral 106 denotes an autofocus (hereinafter referred to as AF) processing unit.

  Reference numeral 107 denotes an image sensor, which is a light receiving means or a photoelectric conversion means for converting reflected light from the subject into an electric signal. Reference numeral 108 denotes an A / D converter, which includes a CDS circuit that removes output noise from the image sensor 107 and a non-linear amplifier circuit that is performed before A / D conversion. Reference numeral 109 denotes an image processing unit. Reference numeral 110 denotes a format conversion unit. Reference numeral 111 denotes a high-speed built-in memory (for example, a random access memory or the like (hereinafter referred to as DRAM)). The DRAM 111 is used as a high-speed buffer as temporary image storage means, or as a working memory for image compression / decompression. An image recording unit 112 includes a recording medium such as a memory card and its interface.

  Reference numeral 113 denotes a system control unit (hereinafter referred to as a CPU) that controls the system such as an imaging sequence. Reference numeral 114 denotes an image display memory (hereinafter referred to as VRAM). Reference numeral 115 denotes an image display unit which displays not only an image display but also a display for assisting operations and a camera state, and a shooting screen and a distance measurement area at the time of shooting. Reference numeral 116 denotes an operation unit for operating the camera from the outside. The operation unit 116 includes the following, for example. That is, there are a menu switch for performing various settings such as a shooting function of the image pickup apparatus and a setting at the time of image reproduction, a zoom lever for instructing a zoom operation of the shooting lens, an operation mode switching switch between a shooting mode and a playback mode, and the like. Reference numeral 117 denotes a shooting mode switch, which can select a shooting mode such as a macro mode, a distant view mode, or a sports mode. The distance measuring distance range, the AF operation, and the like are changed according to the shooting mode selected by the user by the shooting mode switch 117.

  Reference numeral 118 denotes a main switch for turning on the system. Reference numeral 119 denotes a photographing standby switch (hereinafter referred to as SW1) for performing a photographing standby operation such as AF or AE, and 120 denotes a photographing switch (hereinafter referred to as SW2) that performs photographing after the operation of SW1.

  Next, the operation of the electronic camera according to the first embodiment will be described with reference to FIGS. FIG. 2 is a flowchart showing the operation of the electronic camera according to the first embodiment. The flowchart shown in FIG. 2 is executed when the system control unit 113 executes a program stored in the memory and cooperates with the AE processing unit 103, the AF processing unit 106, the image processing unit 109, and the like as necessary. . That is, the system control unit 113 cooperates with each unit to realize the exposure control means, the frame rate setting means, the drive range setting means, the drive amount setting means, the speed setting means, and the control means in the present invention.

  In FIG. 2, in step S201, the AE processing unit 103 performs AE processing from the output of the image processing unit 109, and the process proceeds to step S202. In step S202, the state of SW1 (119) is checked. If ON, the process proceeds to step S203, and if not, the process returns to step S201.

  In step S203, an AF operation is performed, and the process proceeds to step S204. Although details of the AF operation will be described later, a focus evaluation value indicating the contrast of a subject in a predetermined area is obtained based on a video output signal obtained via the imaging optical system including the focus lens 104 and the imaging element 107. Then, the position of the focus lens 104 is adjusted so that the focus evaluation value is maximized. Here, the exposure conditions (shutter speed, aperture, sensitivity) during the AF operation are set in the AE process of the immediately preceding step S201. Also, the required exposure time determined by the exposure condition becomes longer than the time per frame at the frame rate set for AF (unit: [fps], hereinafter referred to as the reference frame rate). In this case, an operation for adjusting the frame rate during the AF operation to the exposure time is performed by providing a predetermined blanking period between the frames. Hereinafter, this operation is referred to as variable frame rate.

  In step S204, the state of SW1 (119) is checked. If it is ON, the process proceeds to step S205, and if not, the process returns to step S201. In step S205, the state of SW2 (120) is checked. If it is ON, the process proceeds to step S206. Otherwise, the process returns to step S204. In step S206, a photographing operation is performed, and then the process returns to step S201.

  FIG. 3 is a flowchart showing the AF operation in step S203 of FIG. First, in step S301, a distance measurement area is set as a predetermined area in the screen, and the process proceeds to step S302. In step S302, a scan range corresponding to the shooting mode and focal length is set, and the process proceeds to step S303. Here, the scan range is a range in which the focus lens 104 is driven when focus adjustment is performed, and differs depending on the shooting mode and the focal length. For example, in the distant view mode, the distance measurement distance range is limited to a long distance range, so the scan range is narrower than in the normal shooting mode. Also, if the focal length is different, the moving range of the image plane is different even in the same distance range. For example, if the focal length is long, the moving range of the image plane is widened. Therefore, the scanning range must be wider than when the focal length is short. In step S303, the current frame rate is compared with the reference frame rate. As a result, if the current frame rate is lower than the reference frame rate, the process proceeds to step S305; otherwise, the process proceeds to step S304.

  In step S304, the scan interval is set considering that the current frame rate is the same as the reference frame rate, and the process proceeds to step S306 (scan interval setting (1)). The scan interval is the amount by which the focus lens is driven within one frame of the video output signal when performing focus adjustment. In the scan interval setting (1), the maximum scan interval that can ensure AF accuracy is set based on the scan range set in step S302.

  On the other hand, in step S305, the scan interval is set considering that the current frame rate is lower than the reference frame rate, and the process proceeds to step S306 (scan interval setting (2)). In the scan interval setting (2), the scan interval is set at a narrower interval than the scan interval setting (1). Thereby, even when the actual speed becomes faster than the focus speed (drive speed of the focus lens 104) calculated and set later in step S306, which will be described later, due to the resolution limitation in the control of the motor 105. The number of AF scan points can be ensured.

  Hereinafter, the reason will be described with reference to FIGS. FIG. 4 shows the relationship between the current frame rate and the scan interval, and the relationship between the frame rate and the focus speed. When the desired operation is performed when the scan interval (1) and the focus speed (1) are set based on the current frame rate, the setting is performed as shown in FIG. A predetermined number of AF scan points can be acquired within the AF scan range, and a focus evaluation value can be detected. However, if the actual focus speed becomes faster than the set focus speed (1) due to the restriction due to the resolution in the control of the motor 105, the actual scan interval is larger than the set scan interval as shown in FIG. Will also become wider. As a result, as shown in FIG. 5B, a desired number of AF scan points cannot be ensured within the set AF scan range, and the focus evaluation value peak cannot be detected. Therefore, as shown in FIG. 4, the scan interval setting (2) is performed so that the scan interval becomes narrower than the scan interval setting (1). As a result, even when the actual focus speed is increased, the actual scan interval can be prevented from becoming wider than the scan interval setting (1), and the number of AF scan points can be ensured.

  In step S306, the focus speed is calculated and set based on the current frame rate and the scan interval set in step S304 or step S305, and the process proceeds to step S307. In step S307, the focus lens 104 is driven to the scan start position based on the scan range set in step S302, and the process proceeds to step S308. In step S308, driving of the focus lens 104 is started at the focus speed set in step S306, and the process proceeds to step S309. In step S309, the focus evaluation value in the distance measurement area set in step S301 is acquired, and the process proceeds to step S310. In step S310, the current position of the focus lens 104 is acquired, and the process proceeds to step S311. In step S311, it is checked whether or not the position of the focus lens 104 acquired in step S310 is within the scan range set in step S302. If it is within the scan range, the process returns to step S309, and if not, the process proceeds to step S312. Here, a series of operations from step S309 to step S311 is performed in a time corresponding to one frame of the current frame rate. Further, the focus evaluation value acquired in step S309 and the lens position acquired in step S310 are associated with each other and used for calculating the peak position of the focus evaluation value in step S313 described later. At this time, since the focus lens 104 is driven during the acquisition of the focus evaluation value, the focus lens position at the center timing of the exposure time is calculated and associated with the focus evaluation value.

  In step S312, the driving of the focus lens 104 is stopped, and the process proceeds to step S313. In step S313, the peak position of the focus evaluation value is calculated using the focus evaluation value acquired in step S309 and the corresponding position of the focus lens 104 (obtained in step S310). In step S314, an in-focus determination is made, and the process proceeds to step S315. In step S315, the focus lens 104 is driven to the peak position of the focus evaluation value obtained in step S313, and the AF operation ends.

  As described above, even when the actual focus speed becomes faster than the set focus speed, the number of AF scan points can be secured, and the focus evaluation value peak can be detected.

  In the first embodiment, the scan interval set according to the shooting mode, focal length, and frame rate is changed, but the scan range may be changed without changing the scan interval. For example, when the current frame rate is lower than the reference frame rate in step S303, a method of expanding the scan range to the near side or the far side by a predetermined range may be used.

  Further, when the number of AF scan points cannot be secured, a method of continuing the AF scan until it can be secured may be used. However, this is not effective when the focus drive cannot be continued physically, such as when the scan end position is near the mechanical end.

(Second Embodiment)
Next, a second embodiment will be described. The configuration and basic operation of the electronic camera according to the second embodiment are the same as those in FIGS. 1 and 2 described in the first embodiment, and the following description will focus on differences from the first embodiment.

  FIG. 6 is a flowchart showing the AF operation in step S203 of FIG. First, in step S601, a distance measurement area is set as a predetermined area in the screen, and the process proceeds to step S602. In step S602, a scan range corresponding to the shooting mode and focal length is set, and the process proceeds to step S603. In step S603, a scan interval / focus speed setting operation, which will be described later, is performed, and the flow proceeds to step S604.

  In step S604, the focus lens 104 is driven to the scan start position based on the scan range set in step S602, and the process proceeds to step S605. In step S605, driving of the focus lens 104 is started at the focus speed set in step S603, and the process proceeds to step S606. In step S606, a focus evaluation value is acquired, and the process proceeds to step S607. In step S607, the current position of the focus lens 104 is acquired, and the process proceeds to step S608. In step S608, it is checked whether or not the position of the focus lens 104 acquired in step S607 is within the scan range set in step S602. If it is within the scan range, the process returns to step S606, and if not, the process proceeds to step S609. Here, a series of operations from S606 to S608 is performed for a time corresponding to one frame of the current frame rate. Further, the focus evaluation value acquired in step S606 and the lens position acquired in step S607 are associated with each other and used in the peak position calculation of the focus evaluation value in step S610 described later. At this time, since the focus lens 104 is driven during the acquisition of the focus evaluation value, the focus lens position at the center timing of the exposure time is calculated and associated with the focus evaluation value.

  In step S609, the driving of the focus lens 104 is stopped, and the process proceeds to step S610. In step S610, the peak position of the focus evaluation value is calculated using the focus evaluation value acquired in step S606 and the corresponding position of the focus lens 104 (obtained in step S607). In step S611, an in-focus determination is made, and the process proceeds to step S612. In step S612, the focus lens 104 is driven to the peak position of the focus evaluation value obtained in step S610, and the AF operation ends.

FIG. 7 is a flowchart showing the scan interval / focus speed setting operation in step S603 of FIG. First, in step S701, a scan interval (hereinafter referred to as Scan Step A) corresponding to a preset shooting mode and focal length is acquired, and the process proceeds to step S702. Here, based on the scan range set in step S602, the maximum scan interval that can ensure AF accuracy is set. Here, the AF accuracy can be ensured because a peak evaluation value that can acquire a focus evaluation value of a predetermined score or more within the scan range set in S602 and that is calculated by using the acquired focus evaluation value. Is within a predetermined depth with respect to the actual subject position. In step S702, a necessary focus speed Scan Speed A is calculated using the following equation (1) from the current frame rate and scan interval Scan Step A, and the process proceeds to step S703.
Scan Speed A = Int (Scan Step A / Current Rate) (1)

  In step S703, it is examined whether Scan Speed A can be output in consideration of the resolution calculated by the number of divisions set in the motor control and the operation clock. As a result, if it is determined that Scan Speed A can be output, the process proceeds to step S704, and if not, the process proceeds to step S705. In step S704, the scan interval is set to Scan Step A and the focus speed is set to Scan Speed A, and the process proceeds to step S604.

On the other hand, in step S705, the fastest focus speed (hereinafter referred to as "Scan Speed B") that can be obtained at or below Scan Speed A is calculated, and the process proceeds to step S706. In step S706, a scan interval (hereinafter referred to as Scan Step B) is calculated from the Scan Speed B and the current frame rate using the following equation (2), and the process proceeds to step S707. In step S707, the scan interval is set to Scan Step B and the focus speed is set to Scan Speed B, and the process proceeds to step S604.
Scan Step B = Int (Scan Speed B * Current Rate) (2)

  As described above, when it is determined that the actual focus speed will be higher than the set focus speed, the AF scan score can be secured by reducing the focus speed to a speed that can be obtained, and focus evaluation A value peak can be detected.

  Although the present invention has been described in detail based on preferred embodiments thereof, the present invention is not limited to these specific embodiments, and various forms within the scope of the present invention are also included in the present invention. included. A part of the above-described embodiments may be appropriately combined.

  The present invention can also be realized by executing the following processing. That is, software (program) that realizes the functions of the above-described embodiments is supplied to a system or apparatus via a network or various storage media, and a computer (or CPU, MPU, etc.) of the system or apparatus reads the program. It is a process to be executed.

  101: Shooting lens, 102: Aperture and shutter, 103: AE processing unit, 104: Focus lens, 105: Motor, 106: AF processing unit, 107: Image sensor, 108: A / D conversion unit, 109: Image processing unit 110: Format conversion unit, 111: DRAM, 112: Image recording unit, 113: System control unit, 114: VRAM, 115: Image display unit, 116: Operation unit, 117: Shooting mode switch, 118: Main switch, 119 : Shooting standby switch, 120: Shooting switch

Claims (7)

A focus evaluation value indicating the contrast of a subject in a predetermined area is obtained based on a video output signal obtained via a photographing optical system including a focus lens and an image sensor, and the focus lens so that the focus evaluation value is maximized. A focus adjustment device for adjusting the position of
Exposure control means for controlling exposure of the shutter speed, aperture, and sensitivity based on the video output signal;
Frame rate setting means for setting a frame rate according to the shutter speed controlled by the exposure control means;
Driving range setting means for setting a range for driving the focus lens when performing focus adjustment;
Drive amount setting means for setting an amount of driving the focus lens in one frame of the video output signal when performing focus adjustment;
The drive speed of the focus lens is calculated based on the amount of driving the focus lens set by the drive amount setting means and the frame rate set by the frame rate setting means, and the calculated drive speed of the focus lens is If it is determined that the calculated focus lens drive speed is set , the calculated focus lens drive speed is set. If it is determined that the calculated focus lens drive speed cannot be output, the fastest focus lens that can be output below the calculated focus lens drive speed. Speed setting means for setting the driving speed of
Focusing device, characterized in that by controlling the motor for driving the focus lens and a control means for driving the focus lens. The drive amount setting unit is configured to select the focus based on a drive speed of the fastest focus lens that can be output below the calculated drive speed of the focus lens set by the speed set unit and a frame rate set by the frame rate setting unit. The focus adjustment apparatus according to claim 1 , wherein a driving amount of the lens is set. The speed setting means is based on the amount of driving the focus lens set according to at least one of the photographing mode and the focal length by the drive amount setting means and the frame rate set by the frame rate setting means. It said calculating a driving speed of the focus lens, focusing device according to claim 1 or 2, characterized in that to determine whether the driving speed of the focus lens put out. The driving range setting means, the focus according to any one of claims 1 to 3, characterized in that to set the range for driving the focus lens according to at least one of the shooting mode and the focal length Adjusting device. The motor, focusing device according to any one of claims 1 to 4, characterized in that a stepping motor which is driven by the excitation pulse generated substantially sinusoidal by dividing a predetermined step . A focus evaluation value indicating the contrast of a subject in a predetermined area is obtained based on a video output signal obtained via a photographing optical system including a focus lens and an image sensor, and the focus lens so that the focus evaluation value is maximized. A focus adjustment device for adjusting the position of
Exposure control means for controlling exposure of the shutter speed, aperture, and sensitivity based on the video output signal;
Frame rate setting means for setting a frame rate according to the shutter speed controlled by the exposure control means;
Driving range setting means for setting a range for driving the focus lens when performing focus adjustment;
Drive amount setting means for setting an amount of driving the focus lens in one frame of the video output signal when performing focus adjustment;
Speed setting means for calculating and setting the drive speed of the focus lens based on the amount of driving the focus lens set by the drive amount setting means and the frame rate set by the frame rate setting means;
A control method of a focus adjusting device comprising a control means for controlling the motor for driving the focus lens to drive the focus lens,
The speed setting means sets the calculated drive speed of the focus lens when determining that the calculated drive speed of the focus lens can be output, and determines that the calculated drive speed of the focus lens cannot be output when the calculated speed of the focus lens is determined. A method for controlling a focus adjusting apparatus, comprising: performing a procedure for setting a drive speed of a fastest focus lens that can be obtained at or below a calculated drive speed of the focus lens . A focus evaluation value indicating the contrast of a subject in a predetermined area is obtained based on a video output signal obtained via a photographing optical system including a focus lens and an image sensor, and the focus lens so that the focus evaluation value is maximized. A program for adjusting the position of
Exposure control means for controlling exposure of the shutter speed, aperture, and sensitivity based on the video output signal;
Frame rate setting means for setting a frame rate according to the shutter speed controlled by the exposure control means;
Driving range setting means for setting a range for driving the focus lens when performing focus adjustment;
Drive amount setting means for setting an amount of driving the focus lens in one frame of the video output signal when performing focus adjustment;
The drive speed of the focus lens is calculated based on the amount of driving the focus lens set by the drive amount setting means and the frame rate set by the frame rate setting means, and the calculated drive speed of the focus lens is If it is determined that the calculated focus lens drive speed is set, the calculated focus lens drive speed is set. If it is determined that the calculated focus lens drive speed cannot be output, the fastest focus lens that can be output below the calculated focus lens drive speed. Speed setting means for setting the driving speed of
The order of the program to control the motor that drives the focus lens cause the computer to function as a control means for driving the focus lens.

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