JP2009244375A - Imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To secure accuracy in focusing, and to shorten the AF time, in scanning-AF where a focus lens is moved by an actuator where the position is feedback-controlled. <P>SOLUTION: The imaging apparatus includes: a focus evaluation means 130, that calculates a focus evaluation value representing the contrast state of a video from a video signal generated by using an imaging device; position control means 110 to 115, that perform the position-feedback control of the actuator 107 that drives the focus lens 106 so as to move the focus lens to a target position; and a focus control means 115, that performs an evaluation value acquiring processing to acquire a plurality of focus evaluation values, while moving the focus lens, and a focusing processing to move the focus lens to the focal position determined, based on the plurality of focus evaluation values. The position control means performs pseudo-speed control of the actuator during the evaluation value acquisition processing. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an imaging apparatus such as a digital still camera that performs position feedback control of an actuator to perform autofocus (AF).

  As an actuator for moving a focus lens in an image pickup apparatus, a stepping motor is often used, but recently, as disclosed in Patent Document 1, there is little noise and vibration, and high speed is excellent. Sometimes linear motors are used.

  A linear motor is an actuator based on the premise that position feedback control is performed so that the deviation between the current position (detected position) of the drive object and the target position is zero, that is, the feedback loop has good response characteristics. The object can be moved at high speed. Therefore, the use of a linear actuator for driving the focus lens makes it possible to increase the AF speed.

  Some digital still cameras perform so-called scan AF. In scan AF, a plurality of focus evaluation values indicating the contrast state of an image are acquired from the image signal while moving (scanning) the focus lens between the infinity end and the close end. Based on the plurality of focus evaluation values, the focus lens position where the maximum focus evaluation value is obtained is determined as the focus position, and the focus lens is moved to the focus position.

  However, in a digital still camera that performs scan AF, if a linear actuator is used to drive the focus lens, it is difficult to move the focus lens at a predetermined speed in normal position feedback control, and the following problems arise. . That is, if the moving speed of the focus lens when scanning the focus lens is too fast, it is difficult to obtain an accurate focus evaluation value at each focus lens position for acquiring the focus evaluation value. As a result, the focusing accuracy decreases.

Patent Document 1 discloses a video camera that performs position feedback control a plurality of times while updating a target position for each predetermined period (small movement amount) so as to move a focus lens at a predetermined average speed with respect to a linear motor. It is disclosed. Such control enables pseudo speed control of the focus lens. In the video camera of Patent Document 1, the focus lens is moved slowly in an area near the in-focus position to increase the in-focus accuracy by switching the target position update period according to the focus evaluation value, and in other areas the focus is increased. The time required for AF is shortened by moving the lens quickly.
Japanese Patent No. 3610176

  However, the pseudo speed control disclosed in Patent Document 1 is suitable for moving image shooting by a video camera, and cannot be directly applied to a digital still camera that performs scan AF. Also, in a digital still camera that records a still image, unlike a video camera that continuously captures a subject, the time required for AF is particularly short so as not to miss the shutter chance desired by the photographer. Required.

  The present invention is an imaging apparatus that performs scan AF by moving a focus lens by an actuator that performs position feedback control, such as a linear motor, and can reduce the time required for AF while ensuring good focusing accuracy. An imaging apparatus is provided.

  An imaging apparatus according to one aspect of the present invention includes a focus evaluation unit that calculates a focus evaluation value indicating a contrast state of a video from a video signal generated using an imaging device, and a focus lens that is moved to a target position. Position control means for performing position feedback control of an actuator that drives the focus lens, evaluation value acquisition processing for acquiring a plurality of focus evaluation values while moving the focus lens, and a result determined based on the plurality of focus evaluation values Focus control means for performing a focusing process for moving the focus lens to a focal position. The position control means performs position feedback control a plurality of times while sequentially updating the target position so as to move the focus lens at a predetermined average speed in the evaluation value acquisition process. Position feedback control is performed by fixing the target position to the in-focus position so as to move to the in-focus position at a speed faster than the speed.

  According to the present invention, when acquiring a plurality of focus evaluation values in scan AF, the focus lens can be moved at a predetermined average speed at which an accurate focus evaluation value can be acquired by pseudo speed control. When the focus lens is moved to the in-focus position, the focus lens can be moved at high speed by normal position feedback control. Thereby, it is possible to shorten the time required for the scan AF while ensuring good focusing accuracy.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows the configuration of a digital still camera (imaging device) that is Embodiment 1 of the present invention.

  The optical system of the camera is accommodated in a lens barrel (not shown). In this optical system, reference numeral 101 denotes a variable magnification lens, which performs variable magnification by moving in the optical axis direction. A diaphragm 105 controls the amount of light, and a shutter 127 controls the exposure amount of the image sensor 116. A focus lens 106 performs focus adjustment by moving in the optical axis direction.

  A zoom motor 102 moves the zoom lens 101. A diaphragm motor 104 drives the diaphragm 105. Reference numeral 128 denotes a shutter motor that opens and closes the shutter 127. A motor driver circuit 103 controls the operations of the zoom motor 102, the aperture motor 104, and the shutter motor 128, and controls the voltage or current supplied to the zoom motor 102, the aperture motor 104, and the shutter motor 125. The motor driver circuit 103 receives an instruction to drive the control target motor from the system control unit 115 described later, and controls the operation of the control target motor.

  Reference numeral 107 denotes a focus motor that moves the focus lens 106. The focus motor 107 is composed of a linear actuator as will be described later.

  Reference numeral 116 denotes an image sensor as a photoelectric conversion element that converts a subject image formed by the optical system described above into an electrical signal. The image sensor 116 is configured by a CCD sensor or a CMOS sensor.

  Reference numeral 117 denotes an A / D converter including a CDS circuit that removes noise included in the output from the image sensor 116 and a non-linear amplifier circuit that performs non-linear amplification before analog output A / D conversion from the image sensor 116. An image processing unit 118 generates a video signal from the digital signal from the A / D conversion unit 117. Reference numeral 129 denotes a WB processing unit that performs WB (white balance) processing on the video signal generated by the image processing unit 118.

  Reference numeral 131 denotes an AE processing unit. Based on luminance information obtained from the video signal generated by the image processing unit 118 or photometric information obtained by a photometric unit (not shown), an AE control value such as an aperture value or a shutter speed. Is generated.

  An AF processing unit 130 as a focus evaluation unit generates a focus evaluation value by extracting a high frequency component from the video signal generated by the image processing unit 118, and sends the focus evaluation value to the system control unit 115. The focus evaluation value is a value indicating the contrast state (sharpness) of an image, and is also referred to as a contrast evaluation value or an AF evaluation value.

  A format conversion unit 119 converts the video signal into a predetermined format. Reference numeral 120 denotes a memory (DRAM). The DRAM 120 is used as a working memory in a high-speed buffer or image compression / decompression process.

  An image recording unit 121 records a recording image (still image) on a recording medium such as a semiconductor memory or an optical disk.

  Reference numeral 115 denotes a system control unit that performs processing such as an imaging sequence and an AF sequence. The system control unit 115 functions as a focus control unit. In this embodiment, the system control unit 115 performs scan AF including the following processing as an AF sequence. In the scan AF, an evaluation value acquisition process for acquiring a plurality of focus evaluation values while moving the focus lens 106, a focus position is determined based on the plurality of focus evaluation values, and the focus lens 106 is moved to the focus position. Focusing process to move. In addition, before the evaluation value acquisition process, a start process for moving the focus lens 106 to the start position of the evaluation value acquisition process is also included.

  Reference numeral 108 denotes a position encoder for detecting the position (current position) of the focus lens 106. Reference numerals 113 and 112 denote an amplification circuit and a differentiation circuit for amplifying and differentiating the output from the position encoder 108, respectively. The output of the position encoder 108 is also supplied to the system control unit 115.

  Reference numeral 114 denotes a comparison circuit that compares the output from the amplifier circuit 113 (detected position signal corresponding to the current position of the focus lens 106) and the output from the system control unit 115 (target signal corresponding to the target position of the focus lens 106). is there. Reference numeral 111 denotes an integration circuit that integrates the output from the comparison circuit 114 (deviation between the current position and the target position). Position feedback control is performed so that the deviation, which is an output from the comparison circuit 114, becomes zero.

  Reference numeral 110 denotes an adder circuit 110 that adds outputs from the differentiation circuit 112 and the integration circuit 111. The reason why the differentiation circuit 112 is provided will be described later.

  The amplification circuit 113, the differentiation circuit 112, the comparison circuit 114, the integration circuit 111, and the addition circuit 110 constitute a position control circuit as a position control means together with the system control unit 115.

  Reference numeral 109 denotes a motor driver 109 that controls the driving of the focus motor 107 in accordance with the output from the adder circuit 110.

  Reference numeral 122 denotes an image display memory (hereinafter referred to as VRAM), and reference numeral 123 denotes a display unit that displays an image and various types of information, and includes an LCD, an organic EL, or the like.

  An operation unit 124 is provided with various switches. 133 is a main switch operated to turn on the power. Reference numeral 125 denotes an imaging preparation switch (hereinafter referred to as SW1) for starting an imaging preparation operation such as AF and AE, and 126 denotes an imaging switch (hereinafter referred to as SW2) for starting an imaging operation (main exposure). SW1 and SW2 are turned on by a first stroke operation (half press) and a second stroke operation (full press) of a release button (not shown), respectively.

  Next, the focus motor 107 and the position control circuit will be described in detail. When a linear motor is used as the focus motor 107, a driving force transmission mechanism as in the case of using a rotary type actuator such as a stepping motor or a DC motor becomes unnecessary. For this reason, the configuration for driving the focus motor 107 is simplified, and the size and weight of the camera can be reduced.

  In this embodiment, a moving coil type voice coil motor, which is one of linear motors, is used as the focus motor 107. A focus lens driving mechanism using a voice coil motor is shown in FIG.

  A focus driving mechanism 200 shown in FIG. 2 includes a lens holding frame 202 that holds a focus lens 201 corresponding to the focus lens 106 in FIG. 1, and a yoke 203 and a coil 206 that are fixed to the outer periphery of the lens holding frame 202. Have. The lens holding frame 202 is guided in the optical axis direction by the guide bar 204. One end of the yoke 203 is bonded to the inner peripheral surface of the fixed cylinder 209 constituting the lens barrel of the camera, and the long part on the other end extends in the optical axis direction. The coil 206 is wound around a hobbin 205 provided on the lens holding frame 202.

  A yoke 207 extending in the optical axis direction is fixed by adhesion at a position facing the yoke 203 on the inner periphery of the fixed cylinder 209. A magnet 208 is bonded to the yoke 207. A coil 206 is disposed between the yoke 203 and the yoke 207 (and the magnet 208). The yokes 203 and 207, the magnet 208, and the coil 206 (bobbin 205) constitute a voice coil motor.

  A magnetic field is formed between the yoke 203 and the yoke 207 in the radial direction of the lens barrel. When a current is passed through the coil 206, a driving force for moving the coil 206 in the optical axis direction is generated. Therefore, the lens holding frame 202 integrally forming the hobbin 205 moves in the optical axis direction together with the focus lens 201 held thereby.

  A reference voltage is applied to one side of the coil 206. The motor driver 109 switches the polarity of the current flowing through the coil 206 by applying a voltage that is positive or negative with respect to the reference voltage to the opposite side of the coil 206 (the side where the reference voltage is not applied). Thereby, the drive direction of the focus motor 107 (that is, the focus lens 106) can be changed. Further, the drive amount of the focus lens 106 can be changed by changing the level of the voltage applied to the coil 206.

  The focus motor 107 is subjected to position feedback control by the position control circuit described above. The reason why the moving speed of the focus lens 106 (the differentiation result of the differentiation circuit 112) is fed back by the differentiation circuit 112 is to stabilize the feedback loop control system. In addition, by suppressing the rapid movement of the focus lens 106, it is possible to acquire a natural image displayed on the display unit 123, and the focus lens 106 exceeds the movable range within the lens barrel unit. This is to prevent collision with other members.

  The target signal described above is supplied from the system control unit 115 to the comparison circuit 114. The correlation between the current position of the focus lens 106 and the target position is stored in advance in the DRAM 120 as a data table. The system control unit 115 generates a target signal by referring to the data table according to the detection position signal (current position information) of the focus lens 106 obtained by the position encoder 108 and the target position.

  Next, processing (imaging sequence, AF sequence, etc.) mainly in the system control unit 115 in the present embodiment will be described with reference to FIGS. These processes are executed according to a computer program stored in a memory built in the system control unit 115.

  FIG. 6 is a flowchart showing a shooting preparation operation and a shooting operation of the electronic imaging apparatus according to the first embodiment of the present invention. First, in step S301, the system control unit 115 checks the state of SW1 (125). If it is ON, the system control unit 115 proceeds to step S302. If it is OFF, the system control unit 115 returns to step S301.

  In step S302, the system control unit 115 causes the AE processing unit 131 to perform AE processing for AF, and sets AE control values such as an aperture value and a shutter speed to values suitable for the AF operation. In step S303, the system control unit 115 performs a normal AF operation (scan AF). This AF operation will be described later.

  Next, in step S304, the system control unit 115 causes the AE processing unit 131 to perform the main exposure AE process in a state where the AF operation in step S303 is completed. In step S302 described above, an aperture value and a shutter speed suitable for the AF operation are set. Here, an aperture value and a shutter speed suitable for acquisition of a recording image to be actually recorded (main exposure) are set. .

  Next, in step S305, the system control unit 115 checks the state of SW1 (125) again. If it is ON, the process proceeds to step S306, and if it is OFF, the process returns to step S301.

  In step S306, the system control unit 115 checks the state of SW2 (126). If SW2 (126) is ON, the process proceeds to the next step S307, and if SW2 (126) is OFF, the process returns to step S305.

  In step S307, the system control unit 115 performs an imaging (main exposure) process in a state where focus is obtained. This imaging process will be described later.

  The imaging process shown in step S307 of FIG. 6 will be described in detail using the flowchart of FIG. First, in step S <b> 801, the system control unit 115 controls the aperture 105 and the shutter 127 through the motor driver 103 to expose the image sensor 116 for recording a still image. In step S <b> 802, the system control unit 115 causes the A / D conversion unit 117 to read out charges (analog signal) accumulated in the image sensor 116.

  In step S803, the system control unit 115 causes the A / D conversion unit 117 to convert an analog signal into a digital signal. In step S804, the system control unit 115 causes the image processing circuit 118 to perform various types of image processing on the digital signal output from the A / D conversion unit 117, and generates an image signal. In addition, the system control unit 115 causes the WB processing unit 129 to perform WB adjustment on the image signal.

  In step S805, the system control unit 115 causes the format conversion unit 119 to compress the output image signal (still image) after WB adjustment into a predetermined format such as JPEG suitable for still image recording.

  Finally, in step S806, the system control unit 115 writes and stores the compressed image signal in the recording medium through the image recording unit 121.

  Next, the AF operation (scan AF) in step S303 in FIG. 6 will be described using the flowchart in FIG.

  First, in step S401, the system control unit 115 sets a search range for sampling a plurality of focus evaluation values while associating with the position of the focus lens 106 by the evaluation value acquisition process. In this embodiment, as indicated by the circled arrow 2 in FIG. 4, a plurality of focus evaluation values are sampled by one movement of the focus lens 106 in the search range (hereinafter referred to as a scanning operation). The search range is a specific close distance from the infinity end (may be the close end or a position on the infinity side from the close end).

  Next, in step S402, the system control unit 115 performs start processing for moving the focus lens 106 to the start position of the scanning operation in the search range set in step S401, as indicated by the circled arrow 1 in FIG. . In the present embodiment, the starting position is the infinity end.

  Here, in this embodiment, two control modes are selectively used for the drive method of the focus lens 106, that is, the control method of the focus motor 107. One is a position control mode, and the other is a pseudo speed control mode. The position control mode is set (selected) in the start process and the focusing process in the scan AF, and the pseudo speed control mode is set (selected) in the evaluation value acquisition process. The movement of the focus lens 106 during the focusing process is indicated by an arrow of a circle 3 in FIG.

  Note that both the control of the focus motor 107 in the position control mode and the control of the focus motor 107 in the pseudo speed control mode are position feedback controls for driving the focus lens 106 so as to move the focus lens 106 to the target position.

  In the position control mode, the focus motor 107 is controlled to move the focus lens 106 to a fixed target position at a moving speed determined by a response characteristic of a feedback loop configured for position feedback control of the focus motor 107. To do. Here, the “fixed target position” means a target position that is not updated until the drive of the focus motor 107 is completed. In this embodiment, the “fixed target position” is based on the start position of the scanning operation and a plurality of sampled focus evaluation values. The in-focus position determined by Since the target position is not updated until the end of driving, the focus lens 106 moves from the movement start position to the target position at once.

  In the following description, the “focus position” includes not only the focus lens position that is actually in focus but also the focus lens position that is provisionally determined based on a plurality of focus evaluation values because it cannot be obtained. Including.

  The process of the system control unit 115 in the position control mode will be described with reference to the flowchart of FIG. FIG. 12 shows both the processing in the position control mode and the processing in the pseudo speed control mode.

  In step S <b> 901, the system control unit 115 determines whether or not the focus motor 107 is requested to be driven in the pseudo speed control mode. If it is not a drive request in the pseudo speed control mode, that is, if it is a drive request in the position control mode, the process proceeds to step S906.

  In step S906, the system control unit 115 fixes the target position at the scan operation start position or the focus position, and causes the comparison circuit 114 to drive the driving voltage corresponding to the target position so as to move the focus lens 106 to the target position. Output a signal. As a result, the focus lens 106 moves at a stroke to the target position at a speed faster than the average movement speed in a pseudo speed control mode described later.

  In the pseudo speed control mode, when the focus lens 106 is moved from the start position of the scan operation to the end position of the scan operation, which is the final target position, in the evaluation value acquisition process, the focus lens 106 reaches the end position after a predetermined time. The target position is updated sequentially. In the present embodiment, the target position is updated n times (multiple times) at a cycle faster than the vertical synchronization period. Note that n times here include setting of the first target position as one update. As a result, the focus lens 106 reaches the final target position by n position feedback controls.

  The processing of the system control unit 115 in the pseudo speed control mode will be described with reference to the flowchart of FIG.

  If it is determined in step S901 that the drive request is in the pseudo speed control mode, the process proceeds to step S902. In step S902, the system control unit 115 determines whether or not the current position of the focus lens 106 is the final target position. If the current position is the final target position, the process ends. On the other hand, if the current position of the focus lens 106 has not reached the final target position, the process proceeds to step 903.

  In step S903, the system control unit 115 calculates the movement amount ΔF of the focus lens 106 per position feedback control. This movement amount ΔF is calculated by the following equation (1) from the difference between the movement start position and the final target position (movement end position) of the focus lens 106 and the predetermined average speed Vf of the focus lens 106 in the scanning operation. Calculated.

ΔF = Vf / n (1)
Next, in step S904, the system control unit 115 calculates the target position Fx for moving the focus lens 106 by the current position feedback control, using the following expression (2), with the current position of the focus lens 106 as F0.

Fx = F0 ± ΔF (2)
The sign “±” in Expression (2) is “+” when the focus lens 106 is moved in the closest direction during the scanning operation, and “−” when the focus lens 106 is moved in the infinity direction.

  In step S905, the system control unit 115 supplies a drive voltage signal corresponding to the target position Fx obtained in step S904 to the comparison circuit 114. As a result, the focus lens 106 moves to the target position Fx. Thereafter, the process returns to step S902.

  The system control unit 115 repeats the processing from step S903 to step S905 n times until the current position of the focus lens 106 reaches the final target position in step S902.

  The moving speed of the focus lens 106 for each position feedback control out of n times is a moving speed determined by the response characteristic of the feedback loop, but the average moving speed in one vertical synchronization period is Vf. That is, as shown in the left diagram of FIG. 3, in the position control mode, the focus lens 106 is moved at a high speed determined by the response characteristic of the feedback loop. On the other hand, in the pseudo speed control mode, the focus lens 106 is moved at a predetermined average speed lower than the movement speed in the position control mode by periodically updating the target position.

  The right diagram in FIG. 3 shows the movement locus of the focus lens 106 in the pseudo speed control mode in the left diagram. The thin line in the figure shows the actual movement locus of the focus lens 106 by repeating the position feedback control, and the thick line shows the apparent movement locus of the focus lens 106 obtained by leveling the actual movement locus.

  Next, a start process for moving the focus lens 106 to the start position of the evaluation value acquisition process (scan operation) will be described with reference to FIG.

  First, in step S501, the system control unit 115 sets the control mode of the focus motor 107 to “position control mode”.

  Next, in step S502, the system control unit 115 controls the focus motor 107 in the position control mode so as to move the focus lens 106 to the start position of the scanning operation in the search range determined in step S401 of FIG.

  Next, in step S503, the system control unit 115 checks whether or not the focus lens 106 has reached the start position of the scanning operation, and ends the process if it has reached. If not, the process returns to step S503 and waits for the focus lens 106 to reach the start position of the scanning operation.

  In FIG. 7, when the start process ends in step S402, the process proceeds to step S403, and an evaluation value acquisition process (scan operation) is performed. The evaluation value acquisition process will be described with reference to FIG.

  First, in step S701, the system control unit 115 sets the control mode of the focus motor 107 to the “pseudo speed control mode”.

  Next, in step S <b> 702, the system control unit 115 determines whether the current timing is the driving timing of the focus lens 106. Specifically, since the focus evaluation value is calculated by the AF processing unit 130 in a predetermined cycle, it is determined whether or not the timing is synchronized with the cycle. If it is not the drive timing of the focus lens 106, the process returns to step S702 again to wait for the drive timing. If it is the driving timing of the focus lens 106, the process proceeds to step S703.

  In step S703, the system control unit 115 controls the focus motor 107 in the pseudo speed control mode shown in FIG. 12, and starts moving the focus lens 106 (scanning operation). The average moving speed in the scanning operation is set in advance so that the focus evaluation value can be periodically acquired with necessary accuracy (accuracy) while moving the focus lens 106.

  In step S <b> 704, the system control unit 115 determines whether or not the current time is the acquisition timing of the position information of the focus lens 106. If it is not the acquisition timing, the process returns to step S704 to wait for the acquisition timing. If it is the acquisition timing, the process proceeds to the next step S705.

  In step S <b> 705, the system control unit 115 acquires the position information of the focus lens 106 detected through the position encoder 108 at this time, and stores it in the DRAM 120.

  Next, in step S706, the system control unit 115 determines whether or not the current time is the acquisition timing of the focus evaluation value. If not, the process returns to step S706 and waits for the acquisition timing. If it is the acquisition timing, the process proceeds to the next step S707.

  In step S <b> 707, the system control unit 115 acquires the focus evaluation value at this point from the AF processing unit 130. Then, the acquired focus evaluation value is stored in the DRAM 120 in association with the position of the focus lens 106 acquired in step S705.

  In step S708, the system control unit 115 determines whether the focus lens 106 has reached the end position of the scanning operation. If not, the process returns to step S704, and the process of acquiring the position of the focus lens 106 and the focus evaluation value and storing them in association with each other in the DRAM 120 is repeated (steps S704 to S707). If the end position is reached, the evaluation value acquisition process ends there.

  Through the above evaluation value acquisition processing, a plurality of focus evaluation values corresponding to a plurality of focus lens positions at predetermined intervals within the search range are acquired. Next, the system control unit 115 proceeds to step S404 in FIG. 7 and performs a process of calculating a focus position based on the plurality of focus evaluation values.

  This in-focus position calculation process will be described with reference to FIGS. The focus evaluation value acquired in the search range, except for special cases such as perspective conflicts, takes the focus lens position on the horizontal axis and the focus evaluation value on the vertical axis, and the shape indicating the trajectory of the change is as follows: It becomes a mountain shape as shown in FIG. Therefore, whether or not the locus of change in the focus evaluation value is mountain-shaped is inclined with a difference between the maximum value and the minimum value of the focus evaluation value, and a gradient equal to or greater than a predetermined value (SlopeThr) in the locus. It is determined from the length of the part and the slope of the inclined part. When the change locus of the focus evaluation value is mountain-shaped, it is possible to determine whether or not the focus can be determined, which indicates whether or not the focus position can be calculated.

  The determination result of the in-focus determination is represented by ◯, ×, △ as follows.

  ○: The change locus of the focus evaluation value has a mountain shape, and the focus lens position (peak position) at which the focus evaluation value is maximum can be set as the focus position.

  X: The contrast of the subject is low, the locus of the change in the focus evaluation value is not mountain-shaped, and the in-focus position cannot be calculated.

  Δ: A subject exists outside the subject distance range corresponding to the search range (ΔNEAR if the direction where the in-focus position exists is nearer than the search range, and ΔFAR if the direction is far away And).

  Here, in FIG. 16, focus evaluation values that change along a mountain-shaped locus are shown as A to E. The focus evaluation values that are recognized to be inclined from the top (A) of the change locus are D and E, and the width between D and E is the width L of the focus evaluation value peak. Further, SL1 + SL2, which is the sum of the difference SL1 between A and D and the difference SL2 between A and E, is defined as the slope SL of the focus evaluation value.

  The flowchart in FIG. 13 illustrates the in-focus position calculation process in step S404.

  First, in step S1000, the system control unit 115 obtains a maximum value max and a minimum value min among a plurality of focus evaluation values acquired by the evaluation value acquisition process, and also provides a focus lens position (also called a scan point) that gives the maximum value max. ) Find io.

  In step S1001, the system control unit 115 initializes both the peak width (variable) L and the mountain gradient (variable) SL of the focus evaluation value to zero.

  Next, in step S1002, the system control unit 115 determines that the scan point io giving the maximum focus evaluation value max is the far end in the search range where the scan operation is performed (in this embodiment, the infinity end). Check whether or not. If it is not the far end, the process proceeds to step S1003. If it is the far end, the process skips step S1003 and proceeds to step S1004.

  In step S1003, the system control unit 115 checks the monotonic decrease of the focus evaluation value in the infinity direction.

  Here, the processing for checking the monotonic decrease in the infinity direction in step S1003 will be described with reference to the flowchart of FIG.

  First, in step S1100, the system control unit 115 initializes the counter variable i to io. In the next step S1101, the system controller 115 determines the focus evaluation value d [i] at the scan point i and the focus evaluation value d [1] at the scan point i-1 that is infinity one scan point from i. i-1] is obtained. Then, this difference is compared with a predetermined value SlopeThr.

  If d [i] −d [i−1] ≧ SlopeThr, it is determined that a monotone decrease in the infinity direction has occurred, and the process proceeds to step S1102. In step S1102, the system control unit 115 calculates the length (mountain width) L of the portion where the focus evaluation value is inclined with a slope equal to or larger than SlopeThr and the amount of decrease (gradient) SL in the monotonically decreasing section as Update using (3). Then, the process proceeds to step S1103.

L = L + 1
SL = SL + (d [i] -d [i-1]) (3)
On the other hand, if d [i] −d [i−1] ≧ SlopeThr is not satisfied, the system control unit 115 determines that no monotonic decrease in the infinity direction has occurred, ends the present process, and returns to FIG. The process proceeds to step S1004.

  In step S1103, the system control unit 115 sets i = i−1 and moves the point for checking the monotonic decrease in the infinity direction to the infinity side by one scan point. In next step S1104, the system control unit 115 checks whether or not the counter variable i has become a value (= 0) indicating the far end in the search range. When the value of the counter variable i is 0, that is, when the point for checking monotonic decrease reaches the start position of the scanning operation in the search range, the processing for checking monotonic decrease in the infinity direction is ended. Then, the process proceeds to step S1104 in FIG. As described above, the monotonic decrease from i = io to infinity is examined.

  In FIG. 13, in step S1004, it is checked whether or not the scan point io that gives the maximum focus evaluation value max is the end position on the near side in the search range (here, the closest end). If it is not the close end, the process proceeds to step S1005, and the monotonous decrease in the focus evaluation value in the close direction is checked. If it is the close end, this process is skipped and the process proceeds to step S1006.

  Here, the processing for checking the monotonic decrease of the focus evaluation value in the closest direction in step S1005 will be described with reference to the flowchart of FIG.

  First, in step S1200, the system control unit 115 initializes the counter variable i to io. In the next step S1201, the system control unit 115 sets the focus evaluation value d [i] at the scan point i and the focus evaluation value d [i + 1] at the scan point i + 1 closer to the scan point i by one scan point. Find the difference. Then, this difference is compared with a predetermined value SlopeThr.

  If d [i] −d [i + 1] ≧ SlopeThr, the system control unit 115 determines that a monotonic decrease in the closest direction has occurred, and proceeds to step S1202. In step S1202, the system control unit 115 calculates the length (mountain width) L of the portion where the focus evaluation value is inclined with a slope equal to or greater than SlopeThr and the amount of decrease (gradient) SL in the monotonically decreasing section as Update using (4). Then, the process proceeds to step S1203.

L = L + 1
SL = SL + (d [i] -d [i + 1]) (4)
On the other hand, if d [i] −d [i + 1] ≧ SlopeThr is not satisfied, the system control unit 115 determines that the focus evaluation value has not monotonously decreased in the close direction, and checks the monotonic decrease in the close direction. And the process proceeds to step S1006 in FIG.

  In step S1203, the system control unit 115 sets i = i + 1 and moves the point for checking the monotonic decrease in the closest direction to the closest side by one scan point. In the next step S1204, the system control unit 115 checks whether or not the counter variable i has reached a value (= N) indicating the near end (closest end) in the search range. When the value of the counter variable i is N, that is, the point at which the monotonic decrease is checked reaches the end position of the scanning operation in the search range, the process of checking the monotonic decrease in the closest direction is terminated. Then, the process proceeds to step S1006 in FIG. In this way, the monotonic decrease from i = io in the closest direction is examined.

  In step S1006 in FIG. 13, the system control unit 115 determines that the scan point io that gives the maximum focus evaluation value max is the closest end in the search range in which the scan operation is performed, and d [n] −d [n−. 1] It is determined whether or not SlopeThr. Here, d [n] is the value of the focus evaluation value at the nearest scan point n, and d [n−1] is the focus evaluation value at the scan point n−1 that is one scan point away from n. It is. If d [n] −d [n−1] ≧ SlopeThr, the process proceeds to step S1012; otherwise, the process proceeds to step S1007.

  In step S1007, the system control unit 115 sets the scan point io giving the maximum focus evaluation value max to the infinity side end in the search range in which the scan operation is performed, and d [0] −d [1] ≧ SlopeThr. It is determined whether or not. Here, d [0] is the value of the focus evaluation value at the scan point 0 at the infinity side end, and d [1] is the value of the focus evaluation value at the scan point 1 closer to one scan point than 0. . If d [0] −d [1] ≧ SlopeThr, the process proceeds to step S1011. Otherwise, the process proceeds to step S1008.

  In step S1008, the length (mountain width) L of the slope portion equal to or greater than SlopeThr is equal to or greater than the predetermined value Lo, the average value SL / L of the gradient is equal to or greater than the predetermined value SLo / Lo, and the maximum focus evaluation value is reached. It is determined whether or not the difference between the value max and the minimum value min is greater than or equal to a predetermined value. If L ≧ Lo, SL / L ≧ SLo / Lo, and max−min ≧ predetermined value, the process proceeds to step S1009; otherwise, the process proceeds to step S1010.

  In step S <b> 1009, the system control unit 115 sets the in-focus availability determination result as ◯. Then, interpolation calculation is performed using the maximum focus evaluation value max and the focus evaluation value of one or a plurality of scan points adjacent to the scan point to which the focus evaluation value is given, and the true maximum focus evaluation value is obtained and given. An in-focus position that is a scan point (peak position) is calculated. This in-focus position is determined as a “focus position” in FIG. 9 described later as the focus lens position that is actually in focus.

  In step S1010, the system control unit 115 sets the in-focus availability determination result to x. In this case, the focus lens position corresponding to a specific distance corresponding to the focal length and the imaging mode is determined as the “focus position” in FIG. 9 as a temporary focus position.

  In step S1011, ΔFAR, which indicates that the in-focus position is located on the infinity side of the search range, is used as the focus determination result, and in step S1012, the in-focus position is indicated on the closest side of the search range. NEAR is used as a result of determining whether or not focusing is possible. In this case, the end position on the side where the focus evaluation value is large in the search range is determined as the “focus position” in FIG. 9 as the temporary focus position. As described above, the in-focus position calculation process ends.

  Next, a process of moving the focus lens 106 to the in-focus position (focusing process) will be described with reference to FIG. This process is basically the same as the movement process to the start position of the scan operation described in FIG. 12, except that the target position is the in-focus position determined in step S404 in FIG.

  In step S601 of FIG. 9, the system control unit 115 sets the control mode of the focus motor 107 to “position control mode”.

  Next, in step S602, the system control unit 115 controls the focus motor 107 in the position control mode so as to move the focus lens 106 to the in-focus position determined in steps S1009 to S1012 of FIG. As a result, the focus lens 106 moves at a stroke to the in-focus position that is the target position at a speed faster than the average movement speed in the pseudo speed control mode.

  Next, in step S603, the system control unit 115 checks whether or not the focus lens 106 has reached the in-focus position, and ends the process if it has reached. If not, the process returns to step S603 to wait for the movement of the focus lens 106 to be completed. Thus, the AF operation in step S303 in FIG. 6 is completed, and the imaging process (main exposure) is possible.

  FIG. 5 shows a temporal change in the focus lens position by the processing described so far. That is, first, the focus motor 107 is controlled in the position control mode, and the focus lens 106 moves at high speed to the start position of the scan operation (start process). Next, the focus motor 107 is controlled in the pseudo speed control mode, and the focus lens 106 performs a scanning operation at a predetermined average speed that is lower than the start process (evaluation value acquisition process). Then, the focus motor 107 is controlled in the position control mode, and the focus lens 106 moves to the in-focus position at high speed (in-focus processing).

  As described above, in the start process and the focusing process that simply move the focus lens 106 to the target position in the AF operation, the focus lens 106 is moved at high speed according to the response characteristic of the feedback loop by normal position feedback control. Thereby, the time required for the AF operation can be shortened. On the other hand, in the evaluation value acquisition process of acquiring the focus evaluation value while moving the focus lens 106, the movement of the focus lens 106 compared to the start process and the focusing process is performed by pseudo speed control by a plurality of position feedback controls. Reduce speed. Thereby, an accurate focus evaluation value can be acquired, and final focusing accuracy can be improved.

  In the first embodiment, the AF operation has been described so as to include only the most basic processes of the start process, the evaluation value acquisition process, and the focusing process, but the present invention is not limited to this.

  For example, as shown in FIG. 17, first, a first evaluation value acquisition process is performed with a coarse focus lens position interval in the entire search range (circle 1 in the figure). Next, the second evaluation value acquisition process may be performed at fine focus lens position intervals in the search range where the focus evaluation value obtained by the first evaluation value acquisition process is high (circle 3 in the figure). . Thereby, the in-focus position can be calculated with higher accuracy.

  In this case, in both the first and second evaluation value acquisition processes, the focus motor is controlled in the pseudo speed control mode. Then, the moving speed (predetermined average speed) of the focus lens in the second evaluation value acquisition process that requires a more accurate focus evaluation value may be slower than the moving speed in the first evaluation value acquisition process.

  When the focus lens is moved from the end position of the first evaluation value acquisition process to the start position of the second evaluation value acquisition process (circle 3 in the figure), the focus motor is controlled in the position control mode. . Also in the movement of the focus lens from the end position of the second evaluation value acquisition process to the in-focus position determined by the second evaluation value acquisition process (circled 4 in the figure), the focus motor operates in the position control mode. Be controlled.

  The above-described embodiments are merely representative examples, and various modifications and changes can be made to the above-described embodiments when implementing the present invention.

  For example, even in an AF operation other than scan AF, the position control mode can be changed depending on whether the focus lens movement is required in the shortest time or the pseudo speed control of the focus lens is required. The pseudo speed control mode may be switched.

  Furthermore, in the above-described embodiments, the optical system (lens) integrated imaging apparatus has been described. However, the present invention can also be applied to an interchangeable lens imaging apparatus.

1 is a block diagram illustrating a configuration of an imaging apparatus that is Embodiment 1 of the present invention. FIG. 4 is a diagram illustrating a focus lens driving mechanism using a voice coil motor in the imaging apparatus according to the first embodiment. FIG. 3 is a diagram illustrating a position control mode and a pseudo speed control mode in the first embodiment. FIG. 6 is a diagram illustrating a relationship between a focus evaluation value and an operation of a focus lens in Embodiment 1. FIG. 6 is a diagram illustrating a relationship between a temporal change in the focus lens position and a control mode in the AF operation of the first embodiment. 3 is a flowchart illustrating an imaging sequence according to the first embodiment. 3 is a flowchart showing an AF sequence in the first embodiment. The flowchart which shows the start process in AF sequence. The flowchart which shows the focusing process in AF sequence. The flowchart which shows the evaluation value acquisition process in AF sequence. The flowchart which shows the imaging process in an imaging sequence. The flowchart which shows the switching process of the position control mode and pseudo speed control mode in AF sequence. The flowchart which shows the focusing availability determination process in AF sequence. The flowchart which shows the process which investigates the monotone decrease in the infinity end direction of the focus evaluation value in AF sequence. The flowchart which shows the process which investigates the monotone decrease in the near direction of the focus evaluation value in an AF sequence. The figure explaining the relationship between a focusing availability determination process and a focus evaluation value. FIG. 6 is a diagram illustrating a relationship between a focus evaluation value and an operation of a focus lens in an imaging apparatus that is Embodiment 2 of the present invention.

Explanation of symbols

106 Focus lens 107 Focus motor 108 Position encoder 109 Motor driver 110 Addition circuit 111 Integration circuit 112 Differentiation circuit 113 Amplification circuit 114 Comparison circuit 115 System control unit 125 SW1
126 SW2

Claims (3)

Focus evaluation means for calculating a focus evaluation value indicating a contrast state of a video from a video signal generated by using an image sensor;
Position control means for performing position feedback control of an actuator that drives the focus lens so as to move the focus lens to a target position;
Focus control for performing evaluation value acquisition processing for acquiring a plurality of focus evaluation values while moving the focus lens, and focusing processing for moving the focus lens to a focus position determined based on the plurality of focus evaluation values Means,
The position control means includes
In the evaluation value acquisition process, the position feedback control is performed a plurality of times while sequentially updating the target position so as to move the focus lens at a predetermined average speed.
In the focusing process, the position feedback control is performed with the target position fixed at the focusing position so that the focus lens is moved to the focusing position at a speed faster than the predetermined average speed. An imaging device.   The imaging apparatus according to claim 1, wherein the actuator is a linear actuator. The focus control unit performs a start process of moving the focus lens to a start position of the evaluation value acquisition process before performing the evaluation value acquisition process,
The imaging apparatus according to claim 1, wherein the position control unit performs the position feedback control while fixing the target position at the start position in the start process.