JP2013024884A - Imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the decrease of focus detection accuracy while properly controlling an exposure amount by properly performing diaphragm control.SOLUTION: An imaging apparatus to and from which a lens unit including a focus lens and a diaphragm for adjusting an incident light quantity can be attached and detached includes imaging means for photoelectrically converting a subject image to generate an image signal, generation means for generating a focus signal based on the contrast of the image signal, focus detection means for detecting a focusing direction on the basis of the focus signal while minutely vibrating the attached focus lens, and control means for allowing the imaging means to periodically accumulate a charge and controlling the focus detection means so as not to detect the focusing direction by using the focus signal obtained by the charge accumulation when the imaging means accumulates the charge during the drive of the diaphragm.

Description

  The present invention relates to an image pickup apparatus in which a lens unit having a diaphragm for adjusting the amount of incident light is detachable.

<Wobbling drive during AF>
Conventionally, there has been proposed an imaging apparatus that calculates a contrast evaluation value representing the contrast of a subject image while finely vibrating (wobbling) the focus in the optical axis direction during moving image recording, and performs focus adjustment based on the contrast evaluation value. For example, it is described in Patent Document 1.

<Depth of focus change during AF and its adverse effects>
Conventionally, in an imaging apparatus that performs focus adjustment and moving image shooting based on the contrast of a subject image, if the aperture is changed during focus adjustment, the depth of focus changes, so the contrast evaluation value changes, and the correct focusing result is obtained. It was not obtained, which had an adverse effect on the focusing accuracy. As a countermeasure, there has been proposed an imaging apparatus that performs focus adjustment and moving image shooting with the aperture opened. For example, it is described in Patent Document 2.

<Microstep drive AE>
Conventionally, a diaphragm device that finely controls the aperture control speed of a diaphragm device that is driven by a stepping motor and controls the amount of incident light of the imaging optical system has been proposed. For example, it is described in Patent Document 3.

  As described in Patent Document 3, the control speed of the aperture opening can be finely controlled by selectively switching between the rectangular wave and the microstep waveform for the waveform of the voltage applied to the stepping motor.

<Video shooting with a digital SLR camera>
Also, in recent years, among interchangeable lens digital single-lens reflex cameras that could only shoot still images, there have been provided those that can also shoot moving images.

JP 2005-49577 A JP 2008-40008 A JP-A-6-88985

  As described above, when focus adjustment is performed based on the evaluation result of the contrast of the subject image, if the aperture value is changed during acquisition of the contrast evaluation value, the depth of field changes and the circle of confusion of the subject image changes. As a result, the focusing accuracy is adversely affected. However, there is a limit to controlling the exposure amount only by the charge accumulation time and gain, and the interlocking range for the appropriate exposure amount is greatly narrowed. In addition, heavy use of gain adjustment has also caused image quality degradation.

(Object of invention)
An object of the present invention is to provide an imaging apparatus capable of appropriately controlling aperture and appropriately controlling an exposure amount while suppressing a decrease in focus detection accuracy.

  In order to achieve the above object, an imaging apparatus according to the present invention is an imaging apparatus in which a lens unit including a focus lens and a diaphragm for adjusting the amount of incident light is detachable, and an image signal obtained by photoelectrically converting a subject image An imaging means for generating a focus signal, a generating means for generating a focus signal based on the contrast of the image signal, and a focus detection means for detecting the in-focus direction based on the focus signal while finely vibrating the mounted focus lens When the charge accumulation of the imaging means is performed periodically and the charge accumulation of the imaging means is performed during driving of the diaphragm, the focus direction is obtained using the focus signal obtained by the charge accumulation. And a control means for controlling the focus detection means so as not to detect.

  According to the present invention, it is possible to suppress a decrease in focus detection accuracy while appropriately performing aperture control and appropriately controlling an exposure amount.

It is a block diagram which shows the structure of the digital camera which concerns on the Example of this invention. It is a block diagram explaining the circuit for contrast evaluation value calculation. It is a graph which shows the drive voltage of aperture control. It is a graph which shows the example of control which reduces an aperture drive speed. It is the graph which compared exposure amount control in each camera state. It is a graph explaining the timing of a focus drive and a diaphragm drive. It is a flowchart which shows operation | movement of an Example.

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

  A digital camera that is an embodiment of an imaging apparatus of the present invention will be described with reference to FIGS.

<Configuration of digital camera>
FIG. 1 is a block diagram showing the configuration of a digital camera.

  As shown in FIG. 1, a photographic lens 100 is detachably attached to a digital camera 200 via a lens mounting mechanism of a mount unit (not shown). An electrical contact unit 107 is provided in the mount portion. The electrical contact unit 107 has terminals for communication bus lines including a communication clock line, a data transfer line, a data reception line, and the like. As a result, the digital camera 200 and the photographing lens 100 can communicate with each other. The digital camera 200 communicates with the photographing lens 100 via the electrical contact unit 107 to control driving of the focus lens 101 in the photographing lens 100 and the diaphragm 102 that adjusts the amount of incident light. In FIG. 1, only the focus lens 101 is shown as a lens in the photographic lens 100, but a variable power lens and a fixed lens are also provided in addition to this, and these constitute a lens unit. The digital camera 200 can be equipped with a plurality of types of photographic lenses 100. For example, a photographic lens with a variable aperture driving speed or a photographic lens with a fixed aperture driving speed can be mounted. Yes. In the case of a photographic lens having a variable aperture driving speed, switching is performed between a first control operation for fixing the aperture driving speed and a second control operation for changing the aperture driving speed. It is possible.

  The electrical contact unit 107 is also provided with a communication bus line and a synchronization signal line for transmitting the charge accumulation timing of the image signal from the camera side to the photographing lens side. Note that the synchronization timing may be notified to the lens side using the communication clock line described above, without providing a dedicated line for sending the synchronization signal.

  A light beam from a subject (not shown) is guided to a quick return mirror 203 in the digital camera 200 through a lens unit including a focus lens 101 in the photographing lens 100 and a diaphragm 102. The quick return mirror 203 is disposed obliquely with respect to the optical axis in the photographing optical path. Then, the mirror drive mechanism 213 performs up-down driving so that the light beam from the subject is guided to the first finder optical system (the illustrated position) and the second position is retracted out of the photographing optical path. It is possible to move. The light beam reflected by the quick return mirror 203 reaches the eyes of the photographer through a finder optical system including a finder screen 202, a pentaprism 201, and an eyepiece lens 207 existing on the focus surface.

  When the quick return mirror 203 is raised to the second position, the light beam from the photographing lens 100 reaches the image sensor 212 via the focal plane shutter 210 and the optical filter 211 that are mechanical shutters. The imaging element 212 corresponds to the imaging means of the present invention. The optical filter 211 has a function of cutting infrared rays and guiding only visible light to the image sensor 212 and a function as an optical low-pass filter.

  The focal plane shutter 210 has a front curtain and a rear curtain, and controls transmission and blocking of a light beam from the photographing lens 100.

  In addition, the digital camera 200 includes a system controller 230 that performs overall control. The system controller 230 includes a CPU, an MPU, and the like, and controls the operation of each circuit described later.

  The system controller 230 communicates with the lens controller 108 in the photographic lens 100 via the electrical contact unit 107 via a communication bus line.

  Similarly to the system controller 230, the lens controller 108 is also configured by a CPU, MPU, and the like, and controls the operation of each circuit in the photographing lens 100.

  In communication between the system controller 230 and the lens controller 108, a drive command, a stop command, a drive amount, and a required drive speed for the focus lens 101 in the photographing lens 100 are transmitted from the system controller 230. Further, the system controller 230 transmits a driving amount of the diaphragm 102, a driving speed, and various data transmission requests on the photographing lens side.

  At the time of focus driving, the system controller 230 issues a command for the lens driving direction, driving amount, and driving speed to the lens controller 108 by communication.

  When the lens controller 108 receives a lens driving command from the system controller 230, the lens controller 108 controls the lens driving mechanism 103 that drives the focus lens 101 in the optical axis direction and performs focus driving via the lens driving control unit 104. The lens driving mechanism 103 has a stepping motor as a driving source.

  When the lens controller 108 receives the aperture control command from the system controller 230, the lens controller 108 controls the aperture drive mechanism 105 that drives the aperture 102 via the aperture control drive unit 106, and controls the aperture 102 to the commanded value. The diaphragm drive mechanism 105 is controlled by applying a rectangular waveform conventional waveform or a sinusoidal microstep waveform as a drive voltage by the diaphragm control drive unit 106. FIG. 3 is a graph showing the driving voltage for aperture control, FIG. 3 (a) shows a conventional waveform in 1-2 phase driving, and FIG. 3 (b) shows a waveform in microstep driving.

  The system controller 230 is also connected to the shutter control unit 215 and the photometry unit 209. The shutter control unit 215 controls driving of the front curtain and rear curtain of the focal plane shutter 210 in accordance with a signal from the system controller 230. Further, the drive source of the front and rear curtains of the focal plane shutter 210 is constituted by a spring, and a spring charge is required for the next operation after the shutter travels. The shutter charge mechanism 214 performs this spring charge. Further, the system controller 230 sets an exposure control program for the charge accumulation time, exposure sensitivity, and aperture value of the image sensor 212, which is set based on the exposure amount obtained from the output of a predetermined photometry area in the photometry unit 209 or the image sensor 212. Is stored in the program diagram.

  Further, the system controller 230 transmits a lens driving command to the lens controller 108 and controls the lens driving mechanism 103 via the lens driving control unit 104. Thereby, a subject image is formed on the image sensor 212.

  The camera DSP 227 incorporates a circuit block for calculating a contrast evaluation value (focus signal) used for contrast AF and a circuit block for determining the position and size of a region for calculating the contrast evaluation value. Although these circuit blocks will be described in detail later, the contrast evaluation value here is a value indicating the in-focus state of the optical system including the focus lens 101. The camera DSP 227 and the system controller 230 correspond to the focus detection unit of the present invention that detects the in-focus position while slightly vibrating the focus position of the photographic lens 100.

  The camera DSP 227 is connected to an A / D converter 217 via a timing generator 219 and a selector 222, and is also connected to a work memory 226.

  Here, the image sensor 212 is controlled by an output from a driver 218 that controls horizontal driving and vertical driving for each pixel based on a signal from a timing generator 219 that determines the overall driving timing. Thereby, the subject image is photoelectrically converted to generate and output an image signal. The image signal generated by the image sensor 212 is amplified by the CDS / AGC circuit 216 and converted into a digital signal by the A / D converter 217. In the digital camera 200, a signal output from the timing generator 219 is converted by setting an imaging frame rate of the imaging element 212 by an operation input from the operation switch 232. Thereby, the imaging frame rate of the imaging device 212 is controlled as described above. The imaging frame rate may be changed in accordance with a plurality of shooting modes including a moving image shooting mode for generating a moving image signal and a still image shooting mode for generating a still image signal.

  The output from the A / D converter 217 is input to the memory controller 228 via the selector 222 that selects a signal based on the signal from the system controller 230, and is all transferred to the DRAM 229 that is a frame memory.

  In a video or compact digital camera, a finder display (live view) or the like is performed by the monitor display unit 220 by transferring the transfer result to the video memory 221 periodically (every frame) in a pre-shooting state. In a single-lens reflex digital camera, since the image pickup device 212 is normally shielded by the quick return mirror 203 and the focal plane shutter 210 before shooting, live view display cannot be performed.

  In this regard, the live view operation can be performed by raising the quick return mirror 203 and retracting it from the photographing optical path and then opening the focal plane shutter 210. Further, when the camera DSP 227 or the system controller 230 processes the image signal from the image sensor 212 during live view, a contrast evaluation value indicating the in-focus state of the optical system including the focus lens 101 can be obtained. Then, it is possible to perform focus detection by the contrast evaluation method using the contrast evaluation value.

  At the time of shooting, each pixel data for one frame is read from the DRAM 229 according to a control signal from the system controller 230, subjected to image processing by the camera DSP 227, and temporarily stored in the work memory 226. Then, the data in the work memory 226 is compressed based on a predetermined compression format by the compression / decompression circuit 225, and the result is recorded in the external nonvolatile memory 224. As the nonvolatile memory 224, a nonvolatile memory such as a flash memory is usually used. Further, it may be a hard disk or a magnetic disk.

  Further, the display unit 231 connected to the system controller 230 displays the operation state of the camera set or selected by each switch described later using a display element such as a liquid crystal element, LED (light emitting diode), or organic EL. .

  The operation switch 232 is an operation member that performs operation input for various setting items of the digital camera 200. The release switch SW1 (233) is a switch for starting shooting preparation operations such as photometry and focus detection. The release switch SW2 (234) is a switch for starting a photographing operation (charge accumulation and charge readout operation for acquiring a still image). The live view mode switch 235 is a switch for controlling on / off of the live view display. The moving image switch 236 is a switch for starting a continuous shooting operation (repeated charge accumulation and charge reading operation for acquiring a moving image).

  On the other hand, in the taking lens 100 (lens unit), the lens controller 108 is provided with a memory 109. The memory 109 stores performance information such as the focal length of the photographic lens 100, an open aperture value, and settable aperture drive speed information, and lens ID (identification) information that is unique information for identifying the photographic lens 100. Yes.

  The performance information and the lens ID information are transmitted to the system controller 230 by initial communication when the photographing lens 100 is attached to the digital camera 200, and the system controller 230 stores them in the EEPROM 223.

  In addition, the photographing lens 100 is provided with a lens position information detection unit 110 for detecting position information of the focus lens 101. The lens position information detected by the lens position information detection unit 110 is read by the lens controller 108. The lens position information is used for driving control of the focus lens 101 and is transmitted to the system controller 230 via the electrical contact unit 107.

  The lens position information detection unit 110 includes, for example, a pulse encoder that detects the number of rotation pulses of a motor that constitutes a lens driving mechanism. The output is connected to a hardware counter (not shown) in the lens controller 108, and when the focus lens 101 is driven, the position information is counted by hardware. When the lens controller 108 reads the lens position information, it accesses the internal hardware counter register and reads the stored counter value.

  Next, details of contrast evaluation value calculation in the camera DSP 227 will be described with reference to FIG.

  FIG. 2 is a block diagram for explaining circuit blocks in the camera DSP 227.

  The image signal generated by the image sensor 212 is amplified by the CDS / AGC circuit 216 as described above, and converted into a digital signal by the A / D converter 217. The digitized image data is input to the camera DSP 227 via the selector 222.

  In order to calculate a contrast evaluation value used for contrast AF, image data input to the camera DSP 227 is first input to the focus detection area extraction block 242 via the DSP internal memory 241 in the camera DSP 227. The focus detection area extraction block 242 is a block for trimming the focus detection area and its neighboring image from the image data of the entire screen and sending it to the next contrast evaluation value calculation block 243. The size of the focus detection area is preferably about 1/5 to 1/10 of the outer frame of the screen. The position and size of the focus detection area on the screen can be set for the focus detection area extraction block 242 by the system controller 230. The contrast evaluation value calculation block 243 (generation means) is a block for extracting a predetermined frequency component from the focus detection area and the image in the vicinity thereof by digital filter calculation and sending it to the system controller 230 as a contrast evaluation value. .

<Optimization of aperture drive speed>
Next, a description will be given of a control example in which the exposure difference between the current exposure amount and the target exposure amount is calculated, and the driving speed of the diaphragm 102 is decreased stepwise or continuously within a settable range according to the exposure difference. .

  With regard to the quality of changing the exposure amount, it is desirable to keep the continuity of the photographed image moderately by gradually matching the change in the exposure amount with the change in the amount of light of the subject when recording a moving image. In addition, when a subject image is displayed on the monitor display unit 220 for the purpose of determining the composition before moving image recording (hereinafter referred to as “moving image standby”), since the composition is often changed, a certain amount of exposure is performed. The followability of quantity is required. Also, at the time of still image shooting, it is desirable to adjust the exposure amount at high speed in order to shorten the time until shooting (so-called release time lag). For this reason, the digital camera 200 changes the control of the driving speed of the aperture 102 during moving image recording, during moving image standby, and during still image shooting.

FIG. 4A is a graph showing an example of controlling the driving speed of the diaphragm 102 according to the exposure amount difference. FIG. 4B is a graph showing the photometric value measured and the manner in which the exposure speed control value changes as the driving speed of the diaphragm 102 is updated according to the photometric value. In the graph of FIG. 4B, the dotted line indicates the photometric value, and the solid line indicates the exposure amount control value. In FIG. 4 (b), begins to change the control value of the exposure amount by changing the photometric value at time t _1, the control value of the exposure amount at the time t ₂ catches up with the photometric value. As the photometric value changes again at time t ₃ , the exposure value control value starts to change. As shown in the graph of FIG. 4B, as the control value of the exposure amount approaches the target photometric value, the amount of change in the control value is decreased to improve the live view display quality and the moving image recording quality.

FIG. 5 is a graph comparing the exposure amount control in each camera state during still image shooting, movie recording, and movie standby, with the vertical axis representing the exposure amount difference from the photometric value and the horizontal axis representing the passage of time. It is. 5, a request for exposure adjustment occurs, the still image shooting is performed is driven diaphragm at a first speed, the exposure amount is adjusted in the shortest become time T ₁ in each camera state. Further, during moving image recording, aperture driving starts at a second speed slower than the first speed, and the exposure amount is adjusted over time T ₃ (> T ₁ ) while gradually decreasing the aperture driving speed. Further, at the time of moving image standby, aperture driving starts at a third speed that is slower than the first speed and faster than the second speed, and exposure is performed over time T ₂ (T ₁ <T ₂ <T ₃ ) while gradually decreasing the aperture driving speed. The amount is adjusted. The aperture drive speed (second speed) during movie recording when adjusting the exposure amount and the aperture drive speed (third speed) during movie standby are variable speeds. However, the relationship between the aperture driving speeds is controlled so that the relationship shown in FIG. 5 is maintained.

<Focus drive control and aperture control timing>
Next, focus drive control in the focus detection operation of the present embodiment will be described. FIG. 6 is a graph for explaining the timing of lens driving and diaphragm driving according to the focus detection operation of this embodiment. Here, the horizontal axis indicates time, and the downwardly convex period at the top indicates the synchronization signal. The synchronization signal is synchronized with the charge accumulation timing of the image sensor 212. In FIG. 6, charge accumulation is performed once in 1V, but the present invention is not limited to this. For example, charge accumulation may be performed once at 2V.

FIG. 6A is a graph for explaining the timing when the aperture control amount is small and the aperture control time is short, and FIG. 6B is the graph for explaining the timing when the aperture control amount is large and the aperture control time is long. It is a graph.

In FIG. 6A, the focus lens 101 is controlled so as to periodically reciprocate between a predetermined focus (infinite side and closest side). After the focus lens 101 reaches a predetermined focus position, periods t1, t2, t3, t4, t5,... For storing charges for obtaining a contrast evaluation value are provided. For example, at the Ta drive timing, the drive amplitude is determined by comparing the evaluation value obtained in the period t2 (closest side) with the evaluation value obtained in the period t3 (infinite side). If the evaluation value obtained in the period t3 is larger, the vibration center is moved to the infinite side. The length of the charge accumulation period is adjusted according to the luminance of the subject image. The time from the end of the charge accumulation period to the start of the next charge accumulation period is a diaphragm drive permission period during which the diaphragm can be driven. When aperture driving is performed during contrast AF for exposure amount adjustment, aperture driving is performed within the range of the aperture driving permission period.

In the example of FIG. 6A, a charge accumulation period is provided at all of the close focus position and the infinite focus position, and the diaphragm drive permission period is set between the charge accumulation periods. By comparing the contrast of the subject image before and after the predetermined focus position (closest side and infinity side), it is detected whether the focus lens 101 is driven forward or backward to approach the in-focus state. When the aperture control amount is small, the control is performed as shown in FIG. 6A, and the contrast evaluation values are acquired every time on the close side and the infinite side, so that high focusing accuracy can be maintained.

  On the other hand, FIG. 6B shows an example in which the aperture drive permission period is set to be long, and the aperture drive permission period is changed in accordance with the focus drive control period so that the contrast of the subject images before and after the focus can be compared. (Extended). In the example of FIG. 6B, the charge accumulation period on the near side (or infinite side) of the predetermined focus position is eliminated, and the diaphragm drive permission period is lengthened accordingly. In FIG. 6B as well, periods t1, t2, t3,... In which charge accumulation is performed are provided, but the diaphragm is driven at the timing t3, so the evaluation value obtained by accumulation in period t3 is AF Not used for control. For this reason, at the drive timing of Tb, the evaluation value obtained by the accumulation in the period t3 cannot be used for comparison, and therefore the vibration center is not moved.

  The system controller 230 that performs the operations shown in FIG. 6 and the like corresponds to the control means of the present invention.

  Instead of extending the aperture drive permission period in accordance with the focus drive control period in accordance with the aperture control amount, the diaphragm drive is divided into a plurality of times, and the aperture drive permission period shown in FIG. It can be set.

  Further, for example, an image sensor 212 that performs a focal plane shutter type charge accumulation operation such as a CMOS (Complementary Metal Oxide Semiconductor) may be used as the AF charge accumulation period. Specifically, not the charge accumulation period related to the image frame for acquiring the contrast evaluation value, but a shorter charge accumulation period related to the focus detection area of the image frame may be used.

  In order to perform aperture driving during the aperture driving permission period, an aperture control command is sent from the system controller 230 to the lens controller 108 to take aperture driving timing. The aperture control command includes information about the aperture drive amount and the aperture drive permission period. In addition, the system controller 230 outputs a waveform signal related to the lens drive timing to the lens controller 108, and the lens controller 108 outputs a lens drive command to the aperture control unit 106 based on the waveform signal. Also good. For example, a vertical synchronization signal indicating the start of charge accumulation of the image sensor 212 may be employed as the waveform output.

<Operation of digital camera>
Next, the operation of this embodiment will be described with reference to the flowchart of FIG. Unless specifically described, the following control is performed under the control of the system controller 230.

  First, the live view mode switch 235 is pressed, a live view request is made, and a transition to a state in which exposure amount adjustment is always performed is started. The digital camera 200 is assumed to be powered on in advance. In addition, live view display indicates that a moving image is displayed by displaying the acquired image on the monitor display unit 220 at any time, and the moving image is being recorded or only displayed without being recorded. It does not matter whether it is in a state. The operation switch 232 may be pressed instead of the live view mode switch 235. Note that when this live view request is made, it is assumed that an image is acquired from the image sensor 212 at a constant frame rate.

  First, in step S701, a known general photometry calculation is performed based on the imaging output of a predetermined photometry area, and a difference from the target exposure amount is calculated. After the calculation, based on the program diagram stored in the system controller 230, settings of the aperture change amount at the time of adjusting the exposure amount, the charge accumulation period of the image sensor 212, and the exposure sensitivity are determined. After the determination, the process proceeds to step S702.

  In step S <b> 702, it is determined from the performance information obtained through communication with the photographing lens 100 whether the photographing lens 100 attached to the digital camera 200 is a lens that can change the aperture driving speed. If it is detected that the performance information includes aperture drive speed information that can be set, and the photographing lens 100 is a compatible lens capable of changing the aperture drive speed, the process advances to step S703. If not, the process proceeds to step S704. By proceeding to step S704, the operation is switched to the first control operation in which the driving speed of the diaphragm 102 is fixed. In addition, by proceeding to step S703, the operation is switched to the second control operation in which the drive speed of the diaphragm 102 is variable.

  In step S703, it is determined whether or not the state of the digital camera 200 is the still image recording mode (= still image shooting mode). The state that is not in the still image recording mode is during moving image recording or during moving image standby. If it is the still image recording mode, the process proceeds to step S705. If it is not the still image recording mode, the process proceeds to step S711.

  In step S704, the setting of the aperture driving speed controlled by the exposure amount adjustment is set to the fixed speed because the photographing lens 100 is determined to be unable to change the aperture driving speed. After setting the aperture drive speed, the process proceeds to step S706.

  In step S705, the state of the digital camera 200 is the still image recording mode, and the exposure amount is quickly adjusted in consideration of the release time lag. Therefore, the aperture driving speed is set to a high first speed. The setting information of the aperture driving speed is notified from the system controller 230 to the lens controller 108 through the electrical contact unit 107. The lens controller 108 receives the notification of the aperture drive speed setting, and instructs the aperture controller 106 to determine the aperture drive speed. After setting the aperture drive speed, the process proceeds to step S706.

  In step S706, the charge control time determined in step S701 is notified to the shutter control unit 215. The shutter control unit 215 updates the exposure time by the focal plane shutter 210 after the notification according to the notified charge accumulation time. Also, the exposure sensitivity determined in step S701 is notified to the CDS / AGC 216. The CDS / AGC 216 updates the amplification value of the image signal generated by the image sensor 212 based on the notified exposure sensitivity. After the update, the process proceeds to step S707.

  In step S707, the aperture opening is controlled at a predetermined aperture driving speed by the aperture change amount determined in step S704 or step S701. Here, the determined aperture driving speed is the first speed set in step S705, or a fixed speed for a lens that is determined to be unable to change the aperture control speed in step S704. After aperture control, the process proceeds to step S708.

  In step S708, once the in-focus state is detected, a so-called one-shot AF request, which is a focus detection operation that does not drive the lens for subsequent focusing, is performed by an explicit operation in SW1 (233). It is determined whether it occurred by input. If a one-shot AF request has been generated, the process proceeds to step S709 in response to completion of photometric operation such as aperture control.

  In step S709, known one-shot AF is performed to detect the focus position with the highest contrast while performing focus control at high speed in consideration of the time required for AF (so-called AF time lag) regardless of the quality of the live view display. After AF, the process proceeds to step S710.

  In step S <b> 710, it is determined whether a live view end request is generated by an operation input of the live view mode switch 235. If there is a termination request, the operation of this embodiment is terminated. If there is no end request, in order to continue the exposure adjustment and the continuous AF described in step S720 described later while continuing the live view, the process returns to step S701, and the above-described operation of the present embodiment is performed again.

  In step S711, it is determined whether the digital camera 200 is recording a moving image based on an operation input of the moving image switch 236. If a moving image is being recorded, the process proceeds to step S712. If the moving image is not being recorded, the process proceeds to step 713.

  In step S712, the aperture driving speed is set to a second speed that is slow for moving images. After the setting, the process proceeds to step S714.

  In step S713, the aperture driving speed is set to a third speed that is slower than the first speed and faster than the second speed for live view. After the setting, the process proceeds to step S714.

  In step S714, it is determined whether or not it is the aperture drive permission period described in FIG. 6 for the focus drive (wobbling) performed in step S720 described later. If it is the aperture drive permission period, the process proceeds to step S715 to adjust the exposure amount. If it is not the aperture permission period, the process advances to step S720 to continue the focus drive control.

  In step S715, the shutter control unit 215 is notified of the charge accumulation time determined in step S701. The shutter control unit updates the exposure time by the focal plane shutter 210 after the notification according to the notified charge accumulation time. Also, the exposure sensitivity determined in step S701 is notified to the CDS / AGC 216. The CDS / AGC 216 updates the amplification value of the image signal generated by the image sensor 212 based on the notified exposure sensitivity. After the update, the process proceeds to step S716.

  In step S716, the aperture opening is controlled at the determined aperture driving speed by the aperture change amount determined in step S701. Here, the determined aperture driving speed is the second speed set in step S712 or the third speed set in step S713. After aperture control, the process proceeds to step S717.

  In step S717, it is determined whether the target exposure amount has been reached by aperture drive control at the set aperture drive speed. If the target exposure amount has not been reached, the process proceeds to step S720. If not, the process proceeds to step S718.

  In step S718, in consideration of the quality of live view and moving image recording, it is determined whether the aperture driving speed has already reached the set lower limit as the exposure amount adjustment becomes slower as the exposure amount adjustment approaches the target exposure amount. If it is the set lower limit value, the aperture is continuously controlled to the target exposure amount at that speed, and the process returns to step S715. If it is not the set lower limit value, the process proceeds to step S719.

  In step S719, an exposure difference between the current exposure amount and the target exposure amount is calculated, and the aperture driving speed is reduced within a settable range according to the exposure difference. After the aperture driving speed is lowered, the process returns to step S715 to control the aperture to the target exposure amount.

In step S720, wobbling is performed by reciprocating the focus lens 101 in the focus direction while moving the focus at a lower speed or with a smaller driving amount than in the one-shot AF in consideration of the live view quality. Detect whether it becomes an evaluation value. The focus drive amount D at the time of detection is based on the following expression 1 according to a predetermined permissible circle of confusion δ (for example, the diagonal length of the pixel pitch) and the aperture value F after being controlled in step S716. Controlled.
D = k × F × δ (Formula 1)
Where k is a natural number coefficient (for example, a value of 0.25)

By determining the focus drive amount D based on Equation 1, even if the aperture value F changes by adjusting the exposure amount, the circle of confusion of the subject image can be controlled to be constant. Here, while performing the aperture drive control of FIGS. 4 to 5, the timing is controlled so that the aperture drive can be performed in the aperture drive permission period of FIG. 6, and the focus drive amount D corresponding to the aperture value F is adopted. Thus, both display quality and focus detection accuracy can be achieved. Note that when the focus direction in which a high evaluation value is obtained is detected, the focus lens 101 is driven by a predetermined defocus amount (for example, the focus drive amount D in Expression 1) at a low speed in the focus direction. Continuous AF is realized by repeatedly performing step S720 during live view. If the above-described wobbling drive that forms part of the operation of continuous AF is completed, the process proceeds to step S710.

  By performing the above-described operation, it is possible to appropriately perform aperture control and appropriately control the exposure amount while suppressing a decrease in focus detection accuracy.

DESCRIPTION OF SYMBOLS 100 Shooting lens 101 Focus lens 212 Image pick-up element 227 Camera DSP
230 System Controller 236 Movie Switch 243 Contrast Evaluation Value Calculation Block

Claims (4)

An imaging apparatus that allows a lens unit having a focus lens and a diaphragm to adjust the amount of incident light to be removable.
Imaging means for photoelectrically converting a subject image to generate an image signal;
Generating means for generating a focus signal based on the contrast of the image signal;
A focus detection means for detecting a focusing direction based on the focus signal while finely vibrating the mounted focus lens;
When the charge accumulation of the image pickup means is periodically performed and the charge accumulation of the image pickup means is performed while the diaphragm is being driven, the focus direction is detected using the focus signal obtained by the charge accumulation. An image pickup apparatus comprising: control means for controlling the focus detection means so as not to cause a failure.   The control means is either a first control operation for fixing a driving speed of the diaphragm or a second control operation for changing the driving speed of the diaphragm according to the type of the photographic lens mounted. The imaging apparatus according to claim 1, wherein a period for driving the diaphragm is changed in accordance with the switching.   The imaging apparatus according to claim 2, wherein the control unit changes the driving speed of the diaphragm in accordance with whether or not the moving image is recorded during the second control operation.   In the second control operation, the control means sets the driving speed of the diaphragm to the first speed when recording a moving image, and sets the driving speed of the diaphragm to the first speed when not recording a moving image. The imaging apparatus according to claim 2, wherein the imaging apparatus is changed to a fast second speed.

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