Abstract:
An electronic camera includes an image capturing section, a microphone, a lens driving section, and a focus controlling section. The image capturing section generates image data based on a subject image via an imaging optical system. The microphone records speech outside the camera. The lens driving section includes a motor and a drive mechanism to drive the imaging optical system. The focus controlling section controls the lens driving section according to a focusing state of the subject image and makes different at least one of a continuous driving time of the lens driving section and a drive frequency of the motor during the recording with microphone and that during the non-recording.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2004-376545, filed on Dec. 27, 2004, the entire contents of which are incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an electronic camera having a recording function, and particularly relates to an electronic camera which can suppress recording of an AF operation noise. 
   2. Description of the Related Art 
   In recent years, an electronic camera which electronically records a subject image by an image pickup device has been rapidly widespread. A main function of such an electronic camera is still image shooting, but an electronic camera capable of moving image shooting accompanied by recording and speech recording at the time of still image shooting has been also put into practical use. 
   In the above-described electronic camera, during the recording, driving noise (AF operation noise) of a motor and a drive mechanism which drive an AF lens echoes in a camera casing and is transmitted to a microphone, resulting in recording external speech and the AF operation noise simultaneously. Hence, the electronic camera with a recording function has a problem that the sound quality deteriorates at playback due to the AF operation noise. 
   In relation to the above, Japanese Unexamined Patent Application Publication No. 2002-10123 discloses an electronic camera which, at moving image shooting accompanied by recording, performs a focusing operation only in accordance with a user&#39;s focusing instruction, and suppresses the AF operation noise by suppressing the number of times of AF operations at the sound recording. 
   However, according to the electronic camera in Japanese Unexamined Patent Application Publication No. 2002-10123, the user has to instruct the focusing operation at moving image shooting accompanied by recording, and the operation therefor is very complicated. Further, in the electronic camera in the document, each focusing operation is the same irrespective of during recording or non-recording. Therefore, where the focusing operation is frequently performed, the AF operation noise substantially degrades the sound quality at the time of playback. 
   Furthermore, Japanese Unexamined Patent Application Publication No. 2002-10123, discloses a configuration in which a display regarding a focusing state (whether the out-of-focus amount is within an allowable range) is displayed on a monitor, thereby making it easier for the user to decide about the focusing operation. According to AF TTL contrast detection system in the document, however, the focusing state is determined in a hill-climbing operation, and therefore the operation of acquiring information on the focusing state is the same as the AF operation. Namely, for display of the focusing state as above, the frequent AF operation is needed, thereby making it difficult to improve the sound quality at the time of playback. 
   SUMMARY OF THE INVENTION 
   In view of solving the above-described problems in the related art, the object of present invention is to provide an electronic camera which can automatically perform a focusing operation during the recording and improve sound quality at the time of playback. 
   According to a first aspect of the invention, an electronic camera includes an image capturing section, a microphone, a lens driving section, and a focus controlling section. The image capturing section generates image data based on a subject image obtained via an imaging optical system. The microphone records speech outside the camera. The lens driving section includes a motor and a drive mechanism to drive the imaging optical system. The focus controlling section controls the lens driving section according to a focusing state of the subject image and makes different at least one of a continuous driving time of the lens driving section and a drive frequency of the motor during the microphone&#39;s recording and that during the microphone&#39;s non-recording. 
   According to a second aspect of the invention, the focus controlling section in the first aspect sets shorter the continuous driving time of the lens drive section during the recording than that during the non-recording. 
   According to a third aspect of the invention, the focus controlling section in the first or second aspect sets lower the drive frequency of the motor during the recording than that during the non-recording. 
   According to a fourth aspect of the invention, the image capturing section in any one of the first to third aspects is generatable of moving image data. During moving image shooting accompanied by recording, the focus controlling section performs a first focusing operation within a predetermined time before or immediately after a start of the shooting, and after completing the first focusing operation, switches to a second focusing operation in which at least one of the continuous driving time of the lens driving section and the drive frequency of the motor is different from the first focusing operation. 
   According to a fifth aspect of the invention, the focus controlling section in the fourth aspect sets the continuous driving time of the lens driving section or the drive frequency of the motor in the second focusing operation according to a resolution and a frame rate of the moving image data. 
   According to a sixth aspect of the invention, the focus controlling section in the fourth or fifth performs the second focusing operation intermittently at intervals of an arbitrary focus stopping time after completing the first focusing operation. 
   According to a seventh aspect of the invention, after completing the first focusing operation, the focus controlling section in any of the fourth to sixth aspects performs the second focusing operation when a change in at least one of an exposure condition and a zoom position of the imaging optical system is detected. 
   According to an eighth aspect of the invention, the electronic camera further includes a memory stores therein hyperfocal distance information indicating a relationship between the exposure condition or the zoom position of the imaging optical system and a hyperfocal distance. The focus controlling section stops the second focusing operation when determining according to the hyperfocal distance information that the hyperfocal distance after the change occurs is larger than that before the change occurs. 
   According to a ninth aspect of the invention, the memory in the eighth aspect stores therein the hyperfocal distance information corresponding to each resolution of the moving image data. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The nature, principle, and utility of the invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings in which like parts are designated by identical reference numbers, in which: 
       FIG. 1  is a block diagram of an electronic camera of a first embodiment; 
       FIG. 2  is a schematic diagram showing the placement of an imaging optical system and a microphone of the electronic camera; 
       FIG. 3  is a flowchart showing an AF operation at the time of moving image shooting; 
       FIG. 4  is a flowchart showing an AF operation at the time of moving image shooting in a second embodiment; and 
       FIG. 5  is a flowchart showing an AF operation at the time of moving image shooting in a third embodiment. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Description of First Embodiment 
     FIG. 1  is a block diagram of an electronic camera of a first embodiment.  FIG. 2  is a schematic diagram showing the arrangement of an imaging optical system and a microphone of the electronic camera. The electronic camera of the first embodiment is a digital still camera having a moving image shooting function and can record external speech simultaneously at the time of moving image shooting. 
   The electronic camera includes a photographic lens  10 , a lens driving section  11 , an aperture  12  which adjusts the amount of incident light, an image pickup device  13 , an analog signal processing section  14 , an A/D conversion section  15 , an image processing section  16 , a memory  17 , a microphone  18 , a speech processing section  19 , a card I/F  20 , a display I/F  21 , a monitor  22 , an operation section  23 , a CPU  24 , and a data bus  25  which connects the respective sections. 
   The photographic lens  10  is composed of plural lenses including a zoom lens  30  and a focusing lens  31  for adjusting the focus position. Among the respective lenses, lenses drive-controlled in an optical axis direction are each supported by a lens holding frame  32  provided with a lead nut. The lens holding frame  32  is slidably supported in the optical axial direction by a pair of guide shafts (not shown). 
   The lens driving section  11  includes lead screws  33  which are screwed into the lead nuts and motors  34  each of which drive-controls the photographic lens in the optical axis direction by supplying torque to the lead screw  33 . Two lead screws  33  and two motors  34  described above are provided for driving the zoom lens and driving the focus lens. The lens driving section  11  is formed to be able to output changes in lens position due to a zoom operation and an AF operation by an encoder not shown. 
   The image pickup device  13  is placed on the image space side of the photographic lens  10 . Photodetectors which photoelectrically convert a subject image to generate analog image signals are two-dimensionally arranged on a light-receiving plane (a plane facing the photographic lens  10 ) of the image pickup device  13 . An output of the image pickup device  13  is connected to the analog signal processing section  14 . 
   The analog signal processing section  14  is composed of a CDS circuit which performs correlated double sampling, a gain circuit which amplifies outputs of the analog image signals, a clamp circuit which clamps the waveform of an input signal at a fixed voltage level, and so on. The A/D conversion section  15  converts the analog image signals outputted from the analog image processing section  14  into digital image signals. 
   The image processing section  16  performs processing such as gamma correction, white balance, or the like on the digital image signals outputted from the A/D conversion section  15  to generate shot image data (still image data and moving image data). The image processing section  16  executes compressing/decompressing of the shot image data in a predetermined format. 
   The memory  17  is composed of an SDRAM or the like and has a capacity to store image data corresponding to plural frames. The image data is temporarily stored in this memory  17  before and after image processing by the image processing section  16 . Further, during moving image shooting accompanied by recording, the value of a hyperfocal distance is recorded in the memory  17  at every focus determination. 
   Furthermore, the memory  17  stores a lookup table (hyperfocal distance information) indicating a relationship between an exposure condition such as an f-number and a zoom position of the photographic lens, and the hyperfocal distance. Here, because a change in the allowance of focus depending on the resolution of the moving image data and the hyperfocal distance are closely related, different lookup tables are recorded for respective resolutions of the moving image data. 
   The microphone  18  is attached to a casing  35  of the electronic camera, and its output is connected to the speech processing section  19 . The speech processing section  19  is composed of an AGC circuit, an A/D conversion circuit, and so on. The card I/F  20  has a connector to a recording medium  36 . The recording medium  36  is composed of a publicly known semiconductor memory or the like. The above-described image data (including moving image data with speech) is recorded last on this recording medium  36 . 
   The monitor  22  is connected to the display I/F  21 . A reproduction screen of shot image data, a setting screen to perform various kinds of settings to the camera, and so on are displayed on the monitor  22 . The operation section  23  is composed of a command dial, a cross-shaped cursor key, and so on, and used for various kinds of selective inputs on the setting screen. The resolution, frame rate, and the like of the moving image data can be set on the setting screen. 
   The CPU  24  controls, for example, the lens driving section  11 , the aperture  12 , the image pickup device  13  for charge storage time, and the microphone  18 , switches modes for moving picture shooting and still image shooting, and counts time for determining the timing of a focusing operation, and so on. In the shooting mode, the CPU  24  executes an AF calculation and an AE calculation using the image signals read from the image pickup device  13 . 
   Here, the AF calculation of the CPU  24  is performed by a contrast detection system which uses a principle that there is a correlation between the degree of blur and contrast of an image, and the contrast of the image is maximum when focused. Note that this AF calculation, in many cases, is performed using only image signals on a part (a focus detection area, for example) of the light-receiving plane of the image pickup device  13 . 
   More specifically, the CPU  24  extracts a high-frequency component of a predetermined bandwidth from the output of the image pickup device  13  through a band-pass filter. The CPU  24  integrates the absolute value of the high-frequency component to generate a focus evaluation value regarding the subject image. This focus evaluation value is at maximum when the contrast is at maximum at a focus position. 
   The CPU  24  moves the focusing lens  31  in a predetermined direction and compares the focus evaluation values before and after the movement. When the focus evaluation value after the movement is larger than before the movement, the CPU  24  judges that the contrast is likely to increase, and moves the focusing lens  31  in the same direction and performs the same calculation. On the other hand, when the focus evaluation value after the movement is smaller than before the movement, the contrast is likely to decrease, so that the CPU  24  moves the focusing lens  31  in an opposite direction and performs the same calculation. The CPU  24  repeats the above-described processing to find a peak (focus position) of the focus evaluation value. The above-described operation is generally called a hill-climbing operation. 
   Further, the CPU  24  has a function of making different the settings of the AF operation during the recording and those during the non-recording in order to suppress AF operation noise during the recording. More specifically, as a first means, the CPU  24  sets shorter a continuous driving time of the lens driving section  11  during the recording than that during the non-recording to thereby shorten the length of time when the AF operation noise is generated during the recording. Alternatively, as a second means, the CPU  24  sets lower a drive frequency of the motor  34  during the recording than that during the non-recording to thereby decrease the AF operation speed and decrease the AF operation noise itself during the recording. It is needless to say that the CPU  24  may combine the above-described first means and second means to suppress the AF operation noise during the recording. In the case of the first means, it is desirable that the CPU  24  set the drive frequency of the motor  34  to a value equal to or lower than that during the non-recording, but the CPU  24  can set the drive frequency of the motor  34  slightly higher than that during the non-recording within a range in which the magnitude of the AF operation noise is permissible. 
   Furthermore, in the case of moving image shooting accompanied by recording, the CPU  24  sets the above-described continuous driving time of the lens driving section  11  and drive frequency of the motor  34  according to the resolution and frame rate of the moving image data. Consequently, the AF operation noise can be further suppressed. 
   Generally, the focusing accuracy required for moving images is lower than that for still images, and the required focusing accuracy further lowers when the resolution of the moving image data is low. In this case, even if the AF operation time is shortened or the AF operation speed is decreased, it is likely that the focusing accuracy of the subject image falls within an allowable range. Accordingly, with a decrease in the resolution of the moving image data, the CPU  24  can shorten the continuous driving time of the lens driving section  11  stepwise or lower the drive frequency of the motor  34  stepwise. 
   Further, when the frame rate of the moving image data is low, the increase of the AF operation time and the decrease of the AF operation speed does not affect the moving image data much. Hence, with a decrease in the frame rate of the moving image data, the CPU  24  can extend the continuous driving time of the lens driving section  11  as well as lower the drive frequency of the motor  34 . 
   The electronic camera of the first embodiment is configured as described above. The AF operation in the moving image shooting accompanied by recording will be explained following the flowchart of  FIG. 3 . 
   Step S 101 : Before the shooting, the CPU  24  executes the AF operation and the AE operation in preparation for the start of moving image shooting. Here, in the AF operation (first focusing operation) before the start of shooting in S 101 , the continuous driving time of the lens driving section  11  and the drive frequency of the motor  34  are set similarly to those in normal still image shooting (shooting during the non-recording). 
   Step S 102 : The CPU  24  determines whether a user inputs an instruction to start shooting. If the instruction is inputted (YES side), the CPU  24  proceeds to S 103 . On the other hand, if the instruction is not inputted (NO side), the CPU  24  returns to S 101  and waits for the user to input the instruction to start shooting. 
   Step S 103 : The CPU  24  drives the image pickup device  13  and the microphone  18  to start generation of moving image data with speech. 
   Step S 104 : The CPU  24  stops the first focusing operation along with the start of shooting. When the shooting starts during the first focusing operation, the CPU  24  may abort or complete the first focusing operation. 
   Then, the CPU  24  records a hyperfocal distance at completion of the first focusing operation in the memory  17 . Also, the CPU  24  starts a time count after the completion of the first focusing operation. This time count is used for later-described determination of a focus stopping time (S 106 ). 
   Step S 105 : The CPU  24  changes the settings of the continuous driving time of the lens driving section  11  and the drive frequency of the motor  34  for non-recording (first focusing operation) to those for recording (second focusing operation). The second focusing operation are set to suppress the AF operation noise more than the first focusing operation. For setting the second focusing operation, the CPU  24  determines the above-described continuous driving time and drive frequency during the recording with reference to the resolution and frame rate of the moving image data. Note that the processings in S 103  to S 105  are performed almost concurrently. 
   Step S 106 : The CPU  24  determines whether a predetermined focus stopping time has elapsed from a previous focus determination, according to the time count. If the focus stopping time has elapsed (YES side), the CPU  24  proceeds to S 107 . On the other hand, if the focus stopping time has not elapsed (NO side), the CPU  24  proceeds to S 111 . The focus stopping time in S 106  can be changed appropriately by the CPU  24  in consideration of the continuous driving time and the drive frequency in S 105 , the resolution, the frame rate, or the like of the moving image data. 
   Step S 107 : The CPU  24  determines whether there is a change in f-number (change in exposure condition) or a change in the lens position of the zoom lens  30  after the previous focus determination. With a change in either of them (YES side), the CPU  24  proceeds to S 108 . On the other hand, without a change in both of them (NO side), the CPU  24  proceeds to S 111  after resetting the time count since the AF operation is not required. 
   Step S 108 : The CPU  24  acquires a current hyperfocal distance from the lookup table in the memory  17  according to a current f-number, a current lens position of the zoom lens  30 , and the resolution of the moving image data. 
   Step S 109 : The CPU  24  compares the hyperfocal distance stored in the memory  17  and the current hyperfocal distance (S 108 ) and determines whether the current one is smaller than the stored one. If the current hyperfocal distance is smaller (YES side), the CPU  24  proceeds to S 110 . On the other hand, if the current hyperfocal distance is larger (NO side), it means that the subject is in focus, so that the AF operation is unnecessary. Therefore, the CPU  24  updates the hyperfocal distance in the memory  17  to the hyperfocal distance in S 108 , then resets the time count, and proceeds to S 111 . 
   Step S 110 : The CPU  24  executes the AF operation (second focusing operation) according to the settings in S 105 . After completing the second focusing operation, the CPU  24  first updates the hyperfocal distance in the memory  17  to the hyperfocal distance in S 108 . Then, the CPU  24  resets the time count and proceeds to S 111 . 
   Step S 111 : The CPU  24  determines whether an instruction to end the shooting is inputted. If the end of shooting is inputted (YES side), the CPU  24  ends the moving image shooting accompanied by recording. On the other hand, if the end of shooting is not inputted (NO side), the CPU  24  returns to S 106  and repeats determining as described above. This completes the description of the AF operation of the first embodiment. 
   In the first embodiment, the setting of at least one of the continuous driving time of the lens driving section  11  and the drive frequency of the motor  34  in the second focusing operation during shooting is changed so that the AF operation noise is suppressed more than that in the first focusing operation before the start of shooting. Accordingly, during moving image shooting, the period of time when the AF operation noise is generated is shortened or the AF operation noise is lowered, resulting in a significant improvement in sound quality when the moving image data is played back. 
   Moreover, in the first embodiment, the CPU  24  automatically executes the AF operation also at the time of the moving image shooting accompanied by recording. Therefore, the user can concentrate on shooting without the complicated AF operation, which can reduce failures in shooting due to user&#39;s operation error and the like. 
   In the first embodiment, the second focusing operation is performed intermittently at intervals of a predetermined focus stopping time. Moreover, with no change in f-number and no zoom operation (S 107 ), or with change but when the AF operation is unnecessary as in the case where the hyperfocal distance increases (S 108 ), the second focusing operation is not performed. Hence, according to the first embodiment, the number of times of recording the AF operation noise during moving image shooting is significantly reduced. 
   Description of Second Embodiment 
     FIG. 4  is a flowchart showing an AF operation in moving image shooting accompanied by recording in a second embodiment. The second embodiment is a modified example of the first embodiment, and the first focusing operation is executed immediately after shooting. A configuration of the second embodiment also can obtain nearly the same effect as that of the first embodiment. 
   Here, S 205  to S 210  in the second embodiment correspond to S 106  to S 111 , and a description of overlapping parts will be omitted. The same numerals and symbols will be used to designate components corresponding to components in the first embodiment shown in  FIG. 1  and  FIG. 2 , and a description thereof will be omitted. 
   Step S 201 : Before the start of moving image shooting, the CPU  24  executes the AE operation in preparation for the start of moving image shooting. Then, the CPU  24  determines whether the user inputs an instruction to start shooting. If the instruction is inputted (YES side), the CPU  24  proceeds to S 202 . On the other hand, if the instruction is not inputted (NO side), the CPU  24  waits for the user to input the instruction to start shooting. 
   Step S 202 : The CPU  24  drives the image pickup device  13  and the microphone  18  to start generation of moving image data with speech. 
   Step S 203 : The CPU  24  executes the AF operation (first focusing operation) for a predetermined time along with the start of shooting. Settings of the continuous driving time of the lens driving section  11  and the drive frequency of the motor  34  in the first focusing operation may be the same as settings during the non-recording, or may be settings in which the AF operation noise is suppressed more than that during the non-recording. 
   Then, after completing the first focusing operation, the CPU  24  stores a hyperfocal distance at the end of the first focusing operation in the memory  17 . The CPU  24  also starts a time count from the end of the first focusing operation. 
   Step S 204 : The CPU  24  switches the settings of the continuous driving time of the lens driving section  11  and the drive frequency of the motor  34  in the first focusing operation to those in the second focusing operation. The second focusing operation are set to suppress the AF operation noise more than the first focusing operation. 
   Description of Third Embodiment 
     FIG. 5  is a flowchart showing an AF operation at the time of moving image shooting accompanied by recording in a third embodiment. The third embodiment is a modified example of the first embodiment, and an example in which the CPU  24  makes a determination of the second focusing operation when a change in f-number or a zoom operation is detected and does not make a determination of the focus stopping time. A configuration of the third embodiment can also obtain nearly the same effect as that of the first embodiment. 
   Here, S 301  to S 303  in the third embodiment correspond to S 101  to S 103 , respectively, and a description of overlapping parts will be omitted. 
   Step S 304 : The CPU  24  stops the first focusing operation along with the start of the shooting. Then, the CPU  24  stores a hyperfocal distance at completion of the first focusing operation in the memory  17 . The CPU  24  in the third embodiment does not perform a time count. 
   Step S 305 : The CPU  24  switches the settings of the continuous driving time of the lens driving section  11  and the drive frequency of the motor  34  during the non-recording (the first focusing operation) to those during the recording (the second focusing operation). The above-described second focusing operation is set to suppress the AF operation noise more than the first focusing operation. Note that processings from S 303  to S 305  are performed almost concurrently. 
   Step S 306 : The CPU  24  determines whether there is a change in f-number or a change in the lens position of the zoom lens  30  after a previous focus determination. With a change in either of them (YES side), the CPU  24  proceeds to S 307 . On the other hand, with no change in both of them (NO side), the AF operation is unnecessary, so that the CPU  24  proceeds to S 310 . 
   Step S 307 : The CPU  24  acquires a current hyperfocal distance from the lookup table in the memory  17  according to a current f-number, a current lens position of the zoom lens  30 , and the resolution of the moving image data. 
   Step S 308 : The CPU  24  compares the hyperfocal distance stored in the memory  17  and the current hyperfocal distance (S 307 ) and determines whether the current one is smaller than the stored one. If the current hyperfocal distance is smaller (YES side), the CPU  24  proceeds to S 309 . On the other hand, if the current hyperfocal distance is larger (NO side), that means the subject is in focus, and the AF operation is unnecessary. Therefore, the CPU  24  updates the hyperfocal distance in the memory  17  to the hyperfocal distance in S 307  and proceeds to S 310 . 
   Step S 309 : The CPU  24  executes the AF operation (second focusing operation) according to the settings in S 305 . After completing the second focusing operation, the CPU  24  updates the hyperfocal distance in the memory  17  to the hyperfocal distance in S 307  and proceeds to S 310 . 
   Step S 310 : The CPU  24  determines whether an instruction to end the shooting is inputted. If the end of shooting is inputted (YES side), the CPU  24  ends the moving image shooting accompanied by recording. On the other hand, if the end of shooting is not inputted (NO side), the CPU  24  returns to S 306  and repeats determining as described above. 
   Supplementary Description of Embodiments 
   (1) The above-described embodiments shows the example in which in moving image shooting accompanied by recording, the CPU  24  sets the continuous driving time of the lens driving section and so on during the recording differently from those during the non-recording. However, the present invention is not limited to the above-described embodiments. For example, the present invention includes a case in which, the CPU  24  sets the continuous driving time of the lens driving section and the drive frequency of the motor during recording with the microphone in still image shooting differently from those during the non-recording. 
   (2) According to the above-described embodiments, the CPU  24  may control the second focusing operation regularly at intervals of the focus stopping time without stopping the second focusing operation in response to a change in f-number or the zoom operation. Alternatively, the CPU  24  may set the drive frequency of the motor during the recording lower than that during the non-recording, and control the AF operation continuously during the recording. 
   (3) A focus detecting device of the present invention is not limited to a TTL contrast detection system focus detecting device. For example, it may be a publicly known focus detecting device such as an external light system focus detection device having an optical system different from an imaging optical system or a TTL phase difference detection system focus detecting device. 
   Further, for facilities for understanding, effects of the above-described embodiments will be described supplementally in the below. 
   According to the present invention, it is possible to shorten the time where the AF operation noise occurs or lower the AF operation noise during the recording by making different the continuous driving time of the lens driving section and the drive frequency of the motor during the recording and those during the non-recording. Accordingly, without a special soundproof structure and so on, it is possible to suppress the AF operation noise during the recording, improving the sound quality at the time of playback. Moreover, since the AF operation can be automated even during the recording, the user can concentrate on shooting without the complicated AF operation, which can reduce failures in shooting due to user&#39;s operation error and the like. 
   The invention is not limited to the above embodiments and various modifications may be made without departing from the spirit and scope of the invention. Any improvement may be made in part or all of the components.