JP2014174441A - Image capturing device and control method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce time required for focus adjustment motion and improve focusing accuracy of an image capturing device, which makes focus adjustment using evaluation values that represents image sharpness, by efficiently acquiring the evaluation values.SOLUTION: An image capturing unit generates an image signal from object light entering an image capturing lens 101. An AF processing unit 105 generates focus evaluation values representing sharpness of an object image from the image signal. A system control unit 115 acquires the focus evaluation values while driving a focusing lens, and associates the focus evaluation values with corresponding lens positions. In this process, the system control unit 115 identifies the focus evaluation values influenced by delay in lens motion using property information representing a delay property of initial lens motion, corrects lens positions corresponding thereto, and performs an assessment process for assessing the focal positions. A focusing lens control unit 104 adjusts focus by moving the focusing lens along an optical axis direction in accordance with control commands from the system control unit 115.

Description

  The present invention relates to an imaging apparatus including a focus adjustment apparatus that performs focus detection using the contrast of captured image data, and a control method thereof.

  In autofocus (hereinafter abbreviated as AF) control in a digital camera or the like, a contrast detection method is used. In this method, a high frequency component of a luminance signal obtained from an image sensor using a CCD (Charge Coupled Device), CMOS (Complementary Metal Oxide Semiconductor) or the like is extracted, and the lens position where the component is maximized is aligned. The focus position. How to focus at high speed with high accuracy is an issue in performance competition.

  Patent Document 1 discloses a so-called scanning method. An evaluation value (hereinafter referred to as a focus evaluation value) based on the high frequency component of the luminance signal obtained from the image sensor while driving the focus lens over the entire distance measurement range is calculated and stored in the memory each time. Go. Of the stored values, the lens position corresponding to the maximum value is determined as the in-focus position.

JP 2006-11035 A

While the contrast detection AF is required to increase the speed, in recent years, there has been a strong demand for a reduction in price, size and thickness of a digital camera. For example, from the viewpoint of cost reduction, a stepping motor may be employed as a focus lens drive source. This is because the position detection sensor is unnecessary because the motor can be controlled by open loop control.
Further, from the viewpoint of miniaturization and thinning of the apparatus, the mechanism unit for realizing the AF function has also been devised. For example, in order to reduce the thickness of a lens barrel unit including a zoom lens, a focus lens, and the like, a configuration in which a motor that is a driving source of each lens is separated from the lens is adopted, and the driving force of the motor is transmitted to the lens via a mechanism unit. To communicate.

However, there are technical difficulties in satisfying both the demand for speeding up the AF operation and the demand for cost reduction, size reduction, and thickness reduction of the imaging apparatus. For example, if a focus evaluation value is acquired while driving a focus lens and an accurate focus position is not obtained when it is associated with a lens position, it may cause a decrease in AF accuracy (see FIGS. 2 and 3 for this). And will be described later).
In an imaging apparatus that performs a focus adjustment operation using an evaluation value indicating the sharpness of an image, the present invention efficiently obtains the evaluation value and achieves both a reduction in time required for the focus adjustment operation and an improvement in focusing accuracy. With the goal.

  In order to solve the above-described problems, an apparatus according to the present invention includes an imaging element that photoelectrically converts light imaged through an imaging optical system to generate a video signal, and a focus adjustment that constitutes the imaging optical system. Driving means for moving the lens; evaluation value calculating means for calculating an evaluation value indicating the sharpness of an image using the video signal; storage means for storing characteristic information indicating a delay characteristic when the lens starts to move; While obtaining the evaluation value from the evaluation value calculation means while driving the lens, and specifying the in-focus position by performing a process of associating the position information of the lens when the evaluation value is acquired with the evaluation value, Control means for adjusting the focus by controlling the driving means is provided. The control unit acquires the characteristic information from the storage unit when performing the association process, specifies the exposure condition of the image sensor when the evaluation value is acquired, and affects the delay in the movement of the lens The lens position information corresponding to the evaluation value received is corrected.

  According to the present invention, it is possible to efficiently obtain an evaluation value, and to simultaneously reduce the time required for the focus adjustment operation and improve the focusing accuracy.

FIG. 11 is a block diagram illustrating a configuration example of an imaging apparatus in order to describe the first embodiment of the present invention in conjunction with FIGS. 2 to 10. It is a figure which shows the ideal state at the time of a movement start of a focus lens, and an actual state. It is a figure which shows the influence of the delay at the time of the movement start of the lens from the viewpoint of the focus evaluation value. It is a flowchart which shows AF operation example. It is a flowchart which shows the example of scanning operation | movement. It is a flowchart which shows the example of a delay evaluation value specific process. It is a flowchart which shows the example of a lens position correction process. It is a table | surface which shows delay characteristic information. It is explanatory drawing which illustrates the locus | trajectory and exposure timing of a lens. It is explanatory drawing which shows another example of the locus | trajectory of a lens, and exposure timing. It is a flowchart which shows the example of a focusing determination process which concerns on 2nd Embodiment of this invention. It is a flowchart which shows the AF operation example which concerns on 3rd Embodiment of this invention. It is explanatory drawing which shows the range of a rough scan and a fitting scan which concerns on 3rd Embodiment of this invention. It is explanatory drawing which shows the range of a rough scan and a fitting scan which concerns on 4th Embodiment of this invention.

  Each embodiment of the present invention will be described below. In the following description, when the lens type is not specified, “lens” means a focus lens, that is, a movable lens for focus adjustment, and “lens position” means the position of the focus lens on the optical axis. .

[First Embodiment]
FIG. 1 is a block diagram illustrating a circuit configuration example of an imaging apparatus according to the first embodiment of the present invention. The photographing lens 101 includes a zoom mechanism and constitutes an imaging optical system. The aperture shutter control unit 102 controls driving of an aperture and a shutter that control the light amount. The focus lens control unit 104 drives and controls a focus lens for focusing on the image sensor 108. For the focus lens drive mechanism, for example, a stepping motor is used. The strobe 106 includes a light emitting unit that emits light toward a subject, and light control is performed by an EF processing unit 107. The aperture shutter control unit 102 and the focus lens control unit 104 are provided with an optical element such as a lens (not shown), a mechanism unit such as an aperture / shutter, an actuator for driving them, and a drive control circuit. In addition, there are a D (Digital) / A (Analog) converter and various devices necessary for the control operation.

  The image sensor 108 has a function as light receiving and photoelectric conversion means for converting light from a subject imaged by the imaging optical system into an electric signal. The image sensor 108 is an image sensor using, for example, a CCD (charge coupled device) or a CMOS (complementary metal oxide semiconductor). The image sensor 108 converts incident light into electric charge by photoelectric conversion, and outputs a video signal to the imaging processor 109. The imaging processing unit 109 includes a CDS (Correlated Double Sampling) circuit, a non-linear amplification circuit, and an A (Analog) / D (Digital) conversion unit. The CDS circuit removes output noise of the image sensor 108 by a correlated double sampling method. The nonlinear amplifier circuit performs signal amplification (gain control) on the imaging signal from which noise has been removed by the CDS circuit. The A / D converter converts an imaging signal that is an analog signal into a digital signal.

  The image processing unit 110 performs image processing such as gamma correction and contour correction. Based on the control of the WB (white balance) processing unit 111, white balance processing of image data is executed. The format conversion unit 112 converts the image data acquired from the image processing unit 110 into a predetermined format. The predetermined format is a format suitable for recording on a recording medium in the image recording unit 114 (to be described later) and for use in the operation display unit 117. The memory 113 is a high-speed built-in memory (for example, dynamic random access memory, hereinafter referred to as DRAM). The DRAM 113 is used as a high-speed buffer as temporary image storage means, a working memory in image data compression / decompression processing, or the like. The image recording unit 114 includes a recording medium such as a memory card and its interface unit.

The system control unit 115 includes a CPU (Central Processing Unit), a RAM (Random Access Memory), and a ROM (Read Only Memory), and controls the operation of the entire imaging apparatus. The CPU reads and executes a program stored in advance in the ROM, and uses the RAM as a work area. Processing described in the flowcharts described later is executed by the CPU.
The AE (automatic exposure) processing unit 103 calculates a photometric value corresponding to the brightness of the subject based on the image data obtained by the imaging processing unit 109. Based on this photometric value, the system control unit 115 controls the aperture shutter control unit 102 and the nonlinear amplification circuit of the imaging processing unit 109 to automatically adjust the exposure amount. The AF processing unit 105 extracts a high frequency component from the image data obtained by the imaging processing unit 109 and performs an evaluation value calculation process, that is, a focus evaluation value calculation process. The focus evaluation value calculated by the focus evaluation value calculation is a standard representing the sharpness of the image. The focus evaluation value obtained by the AF processing unit 105 is sent to the system control unit 115, and the focus lens control unit 104 is controlled to perform an automatic focus adjustment (AF) operation.

  An image display memory (hereinafter referred to as VRAM) 116 stores image data from the DRAM 113. The operation display unit 117 displays an image display, a display for assisting operation, a display of a camera state, a captured image at the time of shooting, and the like according to a control command of the system control unit 115. The main switch 118 is operated by the user when the imaging apparatus is turned on. A first switch (hereinafter referred to as SW1) 119 is operated when the user instructs the system control unit 115 to perform a shooting standby operation (shooting preparation operation) such as an AF operation or an AE operation. A second switch (hereinafter referred to as SW2) 120 is operated when the user instructs the system control unit 115 to perform a shooting operation after operating the switch SW1. The posture sensor 121 detects the posture (upward, downward, etc.) of the imaging device and outputs a detection signal to the system control unit 115.

  Next, the difference between the ideal state and the actual state when the focus lens starts moving will be described. While the imaging apparatus is required to increase the AF operation speed, it is required to reduce the price, the size, and the thickness. Therefore, it is necessary to consider the influence on the focus evaluation value. Specifically, when the focus evaluation value is acquired while driving the focus lens, a phenomenon occurs in which the focus evaluation value does not show a correct value near the time when the lens starts moving. This is based on the premise that there is a one-to-one relationship between the actual focus lens position on the optical axis and the drive pulse supplied to the stepping motor, and the drive pulse is handled equivalently to the physical lens position. to cause. However, near the actual lens movement start point, even if the stepping motor does not step out, the lens position and electrical position (number of drive pulses) are temporarily deviated due to the influence of inertia or the like. There may be a state.

FIG. 2A is a schematic diagram showing a position P0 at the focus lens movement start time t0 and a subsequent position P1 at time t1. The focus lens is supposed to move on the optical axis with time as shown in FIG. However, in practice, as shown in FIG. 2B, the focus lens posture may change at time t1. That is, the movement of the front end portion of the lens may be delayed with respect to the movement of the portion close to the drive source side. When compared at the lens position on the optical axis, there is a state where the difference from the position P0 at the time of stop (time t0) is small (the lens should come to the position P1 at time t1, but the actual lens center position) Is a position Q closer to P0 than P1). If the focus evaluation value obtained in such a lens state is associated with the lens position based on the electrical position (number of driving pulses of the stepping motor), a correct state cannot be obtained.
FIG. 3 is a diagram illustrating the influence of delay when the focus lens starts to move. The horizontal axis represents the lens position, and the vertical axis represents the focus evaluation value. It is assumed that when a focus evaluation value is acquired while moving the lens, a focus position exists in the vicinity of the movement start position of the lens. In an ideal state of lens movement (see FIG. 2A), the focus evaluation value acquired during lens movement should be a mountain shape indicated by a solid line in FIG. However, in practice, as described with reference to FIG. 2B, the focus evaluation value acquired during lens movement is a curve indicated by a dotted line in FIG. That is, the level of the first focus evaluation value is lower than (α). Strictly speaking, not the exposure at the ideal position P1 in FIG. 2, but the focus evaluation value exposed at the position Q is obtained due to the influence of the delay. As a result, the shape (left half) of the focus evaluation value indicated by (β) is shifted to the right as a whole from (α). If the in-focus position exists in the vicinity of the lens movement start point, a shift (error) of the in-focus position occurs, and a correct in-focus position cannot be obtained, which causes a decrease in AF accuracy.

In the following, an AF operation capable of efficiently obtaining a focus evaluation value and satisfying both the reduction of the AF operation time and the focusing accuracy while satisfying the demands for low price, miniaturization and thinning will be described. First, the basic flow of the AF operation in this embodiment will be described with reference to FIG.
In step S401, the system control unit 115 determines the moving speed when acquiring the focus evaluation value while moving the focus lens, and the lens movement start position and end position. This moving speed is determined in consideration of the depth of focus and the frame rate during focus adjustment. In next step S402, the system control unit 115 sends a command to the focus lens control unit 104, and moves the lens to the movement start position determined in step S401. Next, a scan operation is executed in S403. The scan operation here is a focus adjustment operation for continuously acquiring a focus evaluation value used for determining whether or not focusing is possible while moving the lens. In the scan operation, processing for acquiring a focus evaluation value in the designated lens movement range is performed according to the driving condition determined in S401, and details thereof will be described later. In step S404, the system control unit 115 performs in-focus determination. In focus determination, the lens position corresponding to the maximum focus evaluation value is specified based on the focus evaluation value obtained in S403. Depending on the moving speed and frame rate of the lens, the interval between the lens positions corresponding to the focus evaluation value that can be acquired may be wide. In the present embodiment, processing for approximating the shape of the original focus evaluation value based on the obtained focus evaluation value and calculating the lens position at which the value becomes maximum is performed. In step S405, the system control unit 115 performs control to move the lens to the in-focus position calculated in step S404.

Next, the scanning operation described in S403 in FIG. 4 will be described in detail with reference to FIG.
First, in S501, the system control unit 115 executes a delay evaluation value specifying process. The delay evaluation value is an evaluation value that is affected by the difference between the actual lens position on the optical axis when the lens starts to move and the electrical position that the system control unit 115 and the focus lens control unit 104 grasp. is there. In step S501, the lens driving conditions and the location where the delay evaluation value is generated when the scanning operation is performed are specified. For the delay evaluation value, a process for specifying the occurrence location when the scanning operation is performed based on the outputs of various sensors mounted on the imaging apparatus is executed. Details of the processing will be described later. In next step S502, the lens starts moving. In step S <b> 503, the AF processing unit 105 determines whether the focus evaluation value calculation process that is periodically executed is completed. If the focus evaluation value calculation processing is not completed in S503, the process returns to S503 again and waits for the completion of the calculation. On the other hand, if the focus evaluation value calculation process has been completed, the process proceeds to S504. In step S <b> 504, processing for acquiring the focus evaluation value calculated by the AF processing unit 105 and temporarily storing it in the RAM of the system control unit 115 is executed. In next step S505, the system control unit 115 counts the number of acquired focus evaluation values (hereinafter referred to as the number of focus evaluation values). The count value is zero at the start of the scanning operation, and the count value increases every time a focus evaluation value is acquired after the start of lens movement. Therefore, it is possible to grasp how many focus evaluation values have been acquired at the time during and after the scanning operation. In the next step S506, lens position correction processing is executed. Although details of the correction process will be described later, basically, lens position information corresponding to each focus evaluation value is determined in consideration of the shutter speed and the delay when the focus lens starts moving.

In step S507, the system control unit 115 stores the focus evaluation value obtained in step S504 and the lens position determined in step S506 in association with each other in the RAM of the system control unit 115. The next S508 is a process for determining whether or not the current lens position has reached the target position (movement end position). If the focus lens control unit 104 determines in S508 that the lens position has not reached the target position, the process returns to S503. On the other hand, if it is determined in S508 that the current lens position has reached the target position, the process proceeds to S509, and the focus lens control unit 104 stops the movement of the lens. Then, the process proceeds to return processing.
As described above, in the scanning operation shown in FIG. 5, continuous focus evaluation values and corresponding lens positions are acquired under the driving conditions determined in S401 of FIG. 4, and the system control unit 115 stores these data in the RAM. Store them in association with each other. The obtained series of focus evaluation values and the lens positions associated therewith are used in the focus determination shown in S404 of FIG.

Next, the delay evaluation value specifying process shown in S501 of FIG. 5 will be described with reference to FIGS.
First, the relationship between the lens movement and the exposure period when affected by the delay in starting the lens movement (hereinafter referred to as lens delay) will be described with reference to FIG. FIG. 9A illustrates an ideal lens trajectory (solid line) and a trajectory (broken line) in which the actual lens delay is modeled when the required speed during the scanning operation is high (for example, 1000 pps). FIG. 9B illustrates an ideal lens trajectory (solid line) and a trajectory (broken line) modeling an actual lens delay when the required speed during the scanning operation is low (for example, 100 pps). The horizontal axis of the graph shows time t, and the vertical axis shows the lens position. Below that, VD (vertical synchronization signal), readout pulse, and exposure state are shown.
In FIG. 9A, an ideal lens trajectory (solid line) is a straight line going up to the right passing through points P1, P2, and P3 starting from the origin. On the other hand, the movement amount of the actual lens locus from the origin until the delay time T _Delay 1000 elapses is zero (stopped state). After that, the lens position rises during the period of T _Recovery 1000 after the delay time T _Delay 1000 has elapsed, passes through points Q1 and P1 _R , and recovers to an ideal lens locus at a position between points P1 and P2. Represented by a graph line.

With reference to FIG. 9A, the lens position corresponding to the focus evaluation value affected by the lens delay will be described. First, the length of one frame period (referred to as T _VD), the delay time T _Delay 1000, and moving period from the relationship between the exposure time (referred to as T _V), the lens of the stop period in the exposure period affected by the lens lag Is obtained. In the present embodiment, the lens position at the center time of the movement period is set as the lens position corresponding to the focus evaluation value. The first lens position at the time of the influence of the lens delay can be calculated from the speed Speed _Recovery 1000 and the moving period at that time. On the other hand, when the lens follows an ideal trajectory, the second lens position at the center time (T _V / 2) of the exposure period can be calculated based on the required speed (lens driving speed) and the exposure period. . The difference between the first lens position and the second lens position is an error between when the lens delay is affected and when it is not. If this error cannot be resolved, it will cause a reduction in focusing accuracy that occurs near the time when the lens starts moving. The delay evaluation value in the present embodiment refers to a focus evaluation value affected by the lens delay.

  In general, an ideal lens trajectory may differ from an actual lens trajectory depending on a required speed of a scanning operation. For example, when the high-speed scanning operation is performed as shown in FIG. 9A, the lens position corresponding to the first focus evaluation value when following an ideal lens locus is set to P1. The lens position when taking into account the delay in the movement of the lens is Q1, and the error due to the influence of the lens delay becomes large. In the case of the low speed scanning operation as shown in FIG. 9B, the error due to the influence of the lens delay is smaller than that in the case of the high speed scanning operation. Thus, the lens position error due to the influence of the lens delay can be calculated if there is information specifying what change the actual locus of movement of the lens shows under what conditions.

In order to specify the delay evaluation value, the system control unit 115 stores characteristic information about the lens delay (hereinafter referred to as delay characteristic information) for specifying the actual lens locus in the ROM area. Specifically, as shown in the table of FIG. 8, for each requested speed when performing the scan operation, three pieces of information of delay time, return time, and return speed are associated and held in the ROM area. The delay time shown in FIG. 8 corresponds to T _Delay 1000 in FIG. 9A, and shows the time until the lens actually starts moving when the focus lens is moved at the required speed. The return time corresponds to T _Recovery 1000 in FIG. 9A, and indicates the time required to return to the ideal lens locus (solid line). The return speed corresponds to Speed _Recovery 1000 in FIG. 9A, and indicates the speed of the lens when returning to an ideal lens locus (solid line). In the present embodiment, an actual lens locus is approximated based on the delay time, the return time, and the return speed, and is used as delay characteristic information. By using this delay characteristic information, the focus evaluation value affected by the lens delay can be specified.

Focus evaluation values can be classified into several types according to the lens state at the exposure timing. For example, the exposure within the delay time is set to “stop state”, the exposure within the return time is set to “return state”, and the state where the influence of the lens delay is eliminated and the exposure is performed at the required speed is set to “stable state”. In this case, it can be classified into the following six types.
(1) Stop state only (2) Stop state and return state (3) Stop state and return state and stable state (4) Return state (5) Return state and stable state (6) Stable state Among these, (1 The focus evaluation value acquired in the case of (5) to (5) corresponds to the delay evaluation value. In particular, the focus evaluation value acquired in the stop state of (1) is referred to as “stop state evaluation value”, and the focus evaluation value acquired in the cases of (2) to (5) is referred to as “return state evaluation value”. And Further, the focus evaluation value acquired by exposure only in the stable state (6) is referred to as a “stable state evaluation value”. As a method for specifying these, the number of evaluation values shown in the following formula is defined when described with reference to FIG.
-Number of delay evaluation values (in any of (1) to (5) above) = (T _Delay 1000 + T _Recovery 1000) / T _VD
(If there is a remainder, add 1)
-Number of evaluation values in the stopped state (in the case of (1) above) = T _Delay 1000 / T _VD
-Number of return state evaluation values (in the case of any of (2) to (5) above) = Number of delay evaluation values-Number of stop state evaluation values

The stable state evaluation value is a focus evaluation value other than the delay evaluation value. Incidentally, it may be used to T _Delay 100, T _Recovery 100 instead of T _Delay 1000, T _Recovery 1000 in the case of FIG. 9 (B).
In this way, it is possible to specify which evaluation value is obtained under what exposure condition with respect to the evaluation value sequentially obtained from the start time of the scanning operation.

Next, the flow of the delay evaluation value specifying process will be described with reference to the flowchart of FIG. The processing of FIG. 6 is executed at the start of the scanning operation in the scanning operation shown in FIG. 5, and the result is used for correction processing of lens position information described later.
First, in S601, a required speed (drive speed) at the time of a scan operation is acquired. In step S602, delay characteristic information is selected. As described above, the delay characteristic information is held for each requested speed (see FIG. 8). For this reason, the delay characteristic information used in the subsequent processing is selected based on the required speed obtained in S601. In step S603, the system control unit 115 identifies a stop state evaluation value. In this process, the stop state evaluation value is specified from the relationship between the delay characteristic information and _TVD , VD (vertical synchronization signal). Similarly, a return state evaluation value is specified in S604. Next, the number of delay evaluation values is calculated in S605. The number of delay evaluation values can be obtained as the sum of the number of stop state evaluation values specified in S603 and the number of return state evaluation values specified in S604. The system control unit 115 temporarily stores the number of delay evaluation values, the number of stop state evaluation values, and the number of return state evaluation values calculated here for use in correction processing of lens position information described later. .

Next, the lens position correction process will be described with reference to FIGS. The process shown in the flowchart of FIG. 7 is executed every time the focus evaluation value is acquired as described in FIG. FIG. 10 is a diagram illustrating lens trajectories and exposure timing. In FIG. 10, an ideal lens locus (solid line) is a straight line going up to the right passing through points P1, P2, P3, and P3 _R starting from the origin. On the other hand, the movement amount of the actual lens locus from the origin until the delay time T _Delay elapses is zero (stop state). After the elapse of the delay time T _Delay , it is represented by a graph line that rises during the period of T _Recovery , passes through points Q2 and P2 _R , and recovers to an ideal lens locus at the position of point P3.

First, in S701, the number of focus evaluation values acquired by the count in S505 in FIG. 5 is compared with the number of delay evaluation values obtained in S605 in FIG. If the acquired number of focus evaluation values is greater than the number of delay evaluation values, that is, if it is specified that the evaluation value is a stable state evaluation value that is not affected by lens delay, the process proceeds to S705. Here, correction processing of lens position information in a stable state is executed. Taking the second exposure timing shown in FIG. 9B as an example, this exposure is not affected by the lens delay. For this reason, the lens moves at a constant speed during the exposure period. In this case, the lens position (see P2) at the time of the center of the exposure period (T _v / 2) is calculated, and that position is associated with the focus evaluation value generated by exposure. This is the correction process in the stable state.

On the other hand, if the acquired focus evaluation value number is equal to or less than the delay evaluation value number in S701, the process proceeds to S702. In S702, it is determined whether or not the acquired number of focus evaluation values is greater than the number of stop state evaluation values obtained in S603 of FIG. If the acquired focus evaluation value number is equal to or smaller than the stop state evaluation value number, that is, if it is determined that the focus evaluation value exposed in the lens stop state is obtained due to the lens delay, the process proceeds to S703. In step S703, the scan operation start position is set as a lens position to be associated with the obtained focus evaluation value.
If it is determined in S702 that the acquired number of focus evaluation values is larger than the number of stopped state evaluation values, that is, it is determined that a focus evaluation value including the influence of exposure at the return speed is obtained due to the influence of lens delay. The process proceeds to S704. In S704, the return state correction process is executed. The return state correction process is a process of calculating the lens position corresponding to the focus evaluation value when the return speed and the return time are generated due to the influence of the lens delay. Specifically, it is specified whether the focus evaluation value is obtained by the exposure in any of the states (2) to (5), and the correction process suitable for each situation is performed. The details are as follows.

(2) In the case of “stop state and return state” (the first exposure shown in FIG. 9A is applicable)
Specific method (judgment condition):
-"Delay evaluation value number> Stop state evaluation value number" and "Delay evaluation value number greater than 1" are satisfied.
• “T _VD × Nth – (delay time + return time)” must be a negative number.
• “Tv − (T _VD × Nth − delay time)> 0” must be satisfied.
Calculation method:
Lens position = P1 _R -Return speed x (T _VD x Nth-Delay time) / 2
Note that P1 _R represents the lens position at t = T _VD .
(3) In the case of “stop state, return state, and stable state” (corresponding to the first exposure in FIG. 9B)
Specific method (judgment condition):
-"Delay evaluation value number> Stop state evaluation value number" and "Delay evaluation value number is 1".
Calculation method:
・ Lens position = P1 _R − Required speed × (T _VD − (Delay time + Return time)) / 2
− Return speed × (T _VD − Delay time) / 2

(4) In the “returned state” (the second exposure in FIG. 10 corresponds)
Specific method (judgment condition):
-“Delay evaluation value number> Stop state evaluation value number” must be satisfied.
• “T _VD × _Nth- (delay time + return time)” must be a negative number.
• “Tv − (T _VD × Nth − delay time) <0” must be satisfied.
Calculation method:
Lens position = P1 _R -Return speed x Tv / 2

(5) In the case of “returned state and stable state” (corresponding to the third exposure in FIG. 10)
Specific method (judgment condition):
-“Delay evaluation value number> Stop state evaluation value number” must be satisfied.
• “T _VD × Nth – (delay time + return time)” must be a positive number.
Calculation method:
・ T _VD × Nth − (Delay time + Return time)> Tv / 2 Lens position = P3 _R − Required speed × Tv / 2
・ Other than above Lens position = P3 _R -Required speed x (T _VD x _Nth- (Delay time + Return time)) / 2
− Return speed × (Tv − T _VD × Nth − (Delay time + Return time)) / 2
P3 _R represents the lens position at t = 3 × T _VD .
The “N” represents a natural number variable, and the lens position indicated by the calculation method is the corrected focus lens position.

In the first embodiment, the delay characteristic information of the focus lens is held in the ROM area of the system control unit 115. Using the delay characteristic information, the lens position corresponding to the focus evaluation value when the lens starts moving is calculated. As a result, the lens position corresponding to the focus evaluation value affected by the lens delay can be calculated in consideration of the actual lens trajectory. Therefore, it is possible to ensure the reliability of the focus evaluation value in the vicinity of the time when the lens starts moving, and to use the focus evaluation value affected by the lens delay without waste. That is, even when a lens delay occurs, an evaluation value affected by the influence can be used effectively.
According to the first embodiment, it is possible to efficiently acquire a focus evaluation value having a correct tendency without adding a new position detection sensor or the like. Therefore, it is possible to realize both shortening of the time required for the AF operation and improvement of focusing accuracy.

[Second Embodiment]
Next, a second embodiment of the present invention will be described. In the second embodiment, focusing accuracy is emphasized, and a focus evaluation value with low reliability is regulated so as not to be used in focusing determination. The basic processing flow is the same as that of the first embodiment, and therefore the differences will be mainly described. In addition, about the component similar to the case of 1st Embodiment, those detailed description is abbreviate | omitted by using the code | symbol already used. The way of omitting such description is the same in the embodiments described later. In the second embodiment, the process of S404 of FIG. 4 is changed as shown in the flowchart of FIG.

  First, in S1101, the result of S501 in FIG. 5 is referred to and how many delay evaluation values are generated by the current scanning operation is specified. In a series of processes from S1102 to S1105, the influence of the lens delay is determined for each acquired focus evaluation value. This is to determine whether or not the acquired focus evaluation value is used in the focus determination. First, in S1102, the system control unit 115 determines whether or not the number of checked focus evaluation values exceeds the number of delay evaluation values. When the number of checked focus evaluation values does not exceed the number of delayed evaluation values, the process proceeds to the next S1103, and the correction amount of the focus evaluation value to be checked is calculated. The correction amount here is the difference between the lens position calculated in S506 in FIG. 5 and the lens position when the lens moves along an ideal locus. In FIG. 9A, the difference between P1 and Q1. It becomes.

In S1104, the correction amount obtained in S1103 is compared with the allowable correction amount. The allowable correction amount is a threshold value for determining whether or not focusing accuracy can be ensured, and is determined in advance. If the correction value is greater than or equal to the threshold value, the process proceeds to S1105. Data for invalidating the checked focus evaluation value so as not to be used for in-focus determination is stored. The data to be invalidated includes information used to exclude it from the focus determination target. Note that the focus evaluation value is treated as a valid evaluation value as long as the focus evaluation value is not rewritten to data to be invalidated. Thereafter, the process returns to S1102 again. On the other hand, if it is determined in S1104 that the correction value is less than the threshold value, the process returns to S1102. Therefore, as long as the corresponding focus evaluation value exists, the determination process in S1104 continues, and if there is no focus evaluation value to be checked in S1102, the process proceeds to S1106. In step S1106, processing for specifying the in-focus position using only valid focus evaluation values is executed.
In the second embodiment, since the evaluation value having a large influence is excluded from the focus evaluation values affected by the lens delay and the focusing position can be specified using the evaluation value having a small influence, the focusing accuracy is lowered. Can be suppressed.

[Third embodiment]
Next, a third embodiment of the present invention will be described. In the third embodiment, the scan operation (focus adjustment operation) is performed when the focus evaluation value affected by the lens delay exists in the vicinity of the in-focus position. This scanning operation (hereinafter referred to as “alignment scanning”) is executed in order to maintain the focusing accuracy. In 3rd Embodiment, FIG. 4 is changed like the flowchart of FIG. The processing from S1201 to S1204 in FIG. 12 is the same as S401 to S404 in FIG. However, it is assumed that the required speed of the scanning operation determined in S1201 (hereinafter referred to as “rough scanning”) is faster than the speed of the alignment scanning determined in S1207 described later.

  In step S1205, the system control unit 115 performs delay determination near the in-focus position. In this determination process, the positional relationship between the in-focus position obtained in the previous S1204 and the delay evaluation value near the start of movement immediately after the start of the scanning operation is determined. FIG. 13 illustrates the coarse scan range and the combined scan range. In the rough scan range 1301 shown in (a), a region 1301a is a region that is strongly influenced by the lens delay, and the correction amount of the lens position is greater than or equal to the threshold value. The area excluding the area 1301a is an area that is not affected by the lens delay. As shown in (a), it is determined whether or not the first in-focus position detected by the coarse scan is included in the execution determination area for the alignment scan. In this embodiment, it is assumed that the execution determination area for the alignment scan is set as an area + α from which the delay evaluation value is acquired, and α is determined in advance as a parameter. As shown in FIG. 13, when the focus position of the coarse scan is P0, the determination result in S1205 is “no delay evaluation value exists near the focus position”. When the first focus position detected by the coarse scan is P1 included in the focus scan execution determination area, the determination result is “the delay evaluation value exists near the focus position”. In S1206, based on the determination result in S1205, it is determined whether or not a delay evaluation value exists in the vicinity of the in-focus position. If it is determined that there is a delay evaluation value in the vicinity of the in-focus position, the process proceeds to S1207. If there is no such delay evaluation value, the process proceeds to S1211. In step S11211, control for moving the focus lens to the in-focus position detected by the coarse scan is performed.

  In step S1207, the system control unit 115 determines a driving condition for the alignment scan. The detection range in this alignment scan is determined so as to include a range 1302 in which accuracy is desired to be guaranteed with the coarse scan focus position as the center, as shown in FIG. In the range 1302, a region 1302a indicates a region affected by an allowable level, and the correction amount of the lens position is less than the threshold value. The area excluding the area 1302a is an area not affected by the lens delay. Thus, when the lens position correction amount corresponding to the focus evaluation value is greater than or equal to the threshold value, the detection range excluding the lens position is determined. A search for the second in-focus position is performed within the range 1302 by the alignment scan. It should be noted that the range 1302 for which accuracy is to be guaranteed is determined so as to ensure the required focusing accuracy in consideration of the depth of focus and the like. In addition, the lens speed in the alignment scan is equal to or less than the speed determined to satisfy the focusing accuracy, and the lens position correction amount of the delay evaluation value is less than the specified value (threshold value) based on the lens delay characteristic information. Determined to be a speed. By determining the range and the speed in this way, it is possible to maintain the focusing accuracy in the in-focus scanning and realize an efficient scanning operation without waste. Note that the processing from S1208 to S1210 is the same as S402 to S404 in FIG.

In the third embodiment, a high-speed scan operation is first performed as a rough scan (first focus adjustment operation). In order to consider the influence of the lens delay, whether or not the focusing scan (second focus adjustment operation) can be performed is determined from the positional relationship between the detected focus position and the area affected by the lens delay. Further, the in-line scan is performed in a narrower range around the focus position of the coarse scan and at a speed that suppresses the influence of the lens delay. Thereby, both the speed and the focusing accuracy in the AF operation can be achieved.
In this embodiment, when determining whether or not to perform the alignment scan, the positional relationship between the in-focus position and the area affected by the lens delay is determined. Furthermore, even if the determination result as to whether or not the maximum lens position correction amount is within a predetermined range (determination reference range) where the focusing accuracy can be maintained is adopted as an execution reference for the fitting scan. Good. In this case, the maximum lens position correction amount is identified from the required speed of the scanning operation based on the delay characteristic information, and the adjustment scan is performed when it is determined that the correction amount is within the predetermined range. .

[Fourth embodiment]
Next, a fourth embodiment of the present invention will be described. In the fourth embodiment, the basic processing flow is the same as that of the third embodiment in that the alignment scan is performed. In the fourth embodiment, the processing content of S1207 in FIG. 12 is changed, and the range for performing the alignment scan is set in consideration of the influence of the lens delay. FIG. 14 illustrates a coarse scan range 1401 and a merged scan range 1403.

  FIG. 14A shows a case where the in-focus position in the coarse scan exists in the alignment scan execution determination area, and the conditions for executing the alignment scan are satisfied. It is assumed that the lens speed during the alignment scan is determined in consideration of the focusing accuracy, the focal depth, and the like. At this time, the number of delay evaluation values affected by the lens delay can be specified by using the required speed of the scan operation and applying the delay evaluation value specifying process described in the first embodiment. Originally, as in a block 1402 indicated by a broken line in FIG. 14, a part of the focus evaluation value acquired within a range in which accuracy is to be guaranteed is affected by the lens delay. Can be identified. The system control unit 115 performs a process of extending a part of the range as shown in FIG. In the alignment scan range 1403, a region 1403a is affected by the lens delay and is excluded from the range where accuracy is desired to be guaranteed. That is, in the area 1403, the area corresponding to the block 1402 is not affected by the lens delay. Thereby, in this embodiment, it is possible to ensure high accuracy in the vicinity of the focus position of the coarse scan.

  Note that the present invention is not limited to the above-described embodiment, and various forms within the scope of the present invention are also included in the technical scope of the present invention. A part of the embodiments may be appropriately combined. For example, the delay characteristic of the movement of the focus lens can change depending on the attitude of the imaging device. Therefore, a process of detecting the posture (upward, downward, etc.) of the imaging device and holding the delay characteristic information illustrated in FIG. 8 in the memory according to the detection information is executed. Focus accuracy can be improved by selecting and using lens delay characteristic information according to the posture detection information. Specifically, in S602 of FIG. 6, processing for acquiring detection information of the posture sensor 121 and selecting a table of lens delay characteristic information corresponding to the posture detection result is executed. Lens delay characteristic information is selected according to the required speed during the scanning operation, and appropriate lens position correction processing is performed.

[Other Embodiments]
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.

DESCRIPTION OF SYMBOLS 104 Focus lens control part 105 AF process part 108 Image pick-up element 109 Imaging process part 115 System control part

Claims (12)

An image sensor that photoelectrically converts light imaged via an imaging optical system to generate a video signal; and
Driving means for moving a focus adjusting lens constituting the imaging optical system;
Evaluation value calculation means for calculating an evaluation value indicating the sharpness of an image using the video signal;
Storage means for storing characteristic information indicating a delay characteristic when the lens starts to move;
While obtaining the evaluation value from the evaluation value calculation means while driving the lens, and specifying the in-focus position by performing a process of associating the position information of the lens when the evaluation value is acquired with the evaluation value, Control means for controlling the driving means to adjust the focus,
The control unit acquires the characteristic information from the storage unit when performing the association process, specifies the exposure condition of the image sensor when the evaluation value is acquired, and affects the delay in the movement of the lens The imaging apparatus corrects position information of the lens corresponding to the evaluation value received.   The control means specifies the evaluation value acquired when the lens is stopped due to a delay in movement of the lens, or the evaluation value acquired when the lens starts moving from the stopped state. The imaging apparatus according to claim 1, wherein the imaging apparatus is characterized. The characteristic information includes information on a delay time until the lens starts to move,
When the control means determines that the lens is in a stopped state within the delay time indicated by the characteristic information, the control means moves the lens as the position of the lens associated with the evaluation value acquired from the evaluation value calculation means. The imaging apparatus according to claim 1, wherein a start position is set. The characteristic information includes information on a return time and a return speed until the lens returns to a trajectory when the lens starts moving without delay.
When it is determined that the lens is moving within the return time indicated by the characteristic information, the control means determines the return speed and the position information of the lens associated with the evaluation value acquired from the evaluation value calculation means. The imaging apparatus according to claim 1, wherein correction is performed using information on an exposure time of the imaging element.   The control means calculates a position of the lens at a central time of an exposure period as position information of the lens associated with the evaluation value determined not to be affected by a delay in movement of the lens. The imaging device according to any one of claims 1 to 4.   The control means identifies the evaluation value affected by the delay in the movement of the lens, and corrects the position information of the lens corresponding to the evaluation value, and if the correction amount is equal to or greater than a threshold value, 6. The imaging apparatus according to claim 1, wherein the evaluation value is excluded from a focus determination target.   When the control means determines that an evaluation value affected by the delay of the lens is present in the vicinity of the first focus position detected in the first focus adjustment operation, the drive is different from the one focus adjustment operation. 7. The second focus position is searched by determining a detection range including the first focus position and its vicinity by a second focus adjustment operation under conditions. The imaging device described in 1.   The control means has a correction amount of the lens position information corresponding to the evaluation value that is affected by a delay in the movement of the lens as a driving condition for performing the second focus adjustment operation, which is smaller than a threshold value. The imaging apparatus according to claim 7, wherein a driving speed of the lens is determined.   When the second focus adjustment operation is performed, the control unit specifies the evaluation value affected by a delay in the movement of the lens, and a correction amount of the position information of the lens corresponding to the evaluation value is a threshold value 9. The imaging apparatus according to claim 7, wherein the detection range excluding the position indicated by the position information of the lens is determined in the case described above.   The control means performs a process of extending the detection range when performing the second focus adjustment operation, and determines the position of the lens corresponding to the evaluation value affected by a delay in movement of the lens. The imaging apparatus according to claim 7 or 8, wherein the second focusing position is searched by excluding from the vicinity of one focusing position. A posture detecting means for detecting the posture of the imaging device;
The imaging device according to claim 1, wherein the control unit acquires detection information from the posture detection unit and selects the corresponding characteristic information. An image sensor that photoelectrically converts light imaged via an imaging optical system to generate a video signal; and
Driving means for moving a focus adjusting lens constituting the imaging optical system;
Evaluation value calculation means for calculating an evaluation value indicating the sharpness of an image using the video signal;
Storage means for storing characteristic information indicating a delay characteristic when the lens starts to move;
A control method executed by an imaging apparatus including a control unit that acquires the evaluation value from the evaluation value calculation unit while driving the lens and controls the driving unit to perform focus adjustment,
Obtaining the evaluation value from the evaluation value calculating means while driving the lens;
When specifying the in-focus position by performing processing for associating the lens position information with the evaluation value when the evaluation value is acquired, the evaluation value is acquired using the characteristic information acquired from the storage unit. And a step of correcting the position information of the lens corresponding to the evaluation value affected by the delay of the start of movement of the lens. .

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