Image pickup apparatus and method for controlling image pickup apparatus

The image pickup apparatus includes an image production unit producing an image by using an output signal from an image pickup unit, a size detection unit detecting a size of a specific object in the image, a zoom control unit performing auto zoom control that automatically provides a specific zoom operation to make the size of the specific object equal or closer to a target value, and a focus control unit performing focus control of an image taking optical system based on a contrast evaluation value obtained from the image. The zoom control unit is configured to restrict the specific zoom operation in the auto zoom control until a determination is made that an in-focus state of the image taking optical system has been obtained by the focus control.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image pickup apparatus such as a digital still camera and a digital video camera, and particularly to an image pickup apparatus having an auto zoom function capable of automatically keeping a constant size of an object in a captured image.

2. Description of the Related Art

Some image pickup apparatuses detects in an image (captured image) produced by using an image pickup element a specific object such as a person's face, and performs autofocus on the detected specific object. Moreover, Japanese Patent Laid-Open No. 09-149311 discloses an image pickup apparatus provided with an auto zoom function capable of performing zoom control so as to keep the size of a detected specific object constant in a captured image even though the distance to the specific object changes. Such an auto zoom function (hereinafter also referred to as “auto zoom”) stores the size of the specific object in the captured image at its start time as a reference size, and automatically performs the zoom control in a telephoto direction or in a wide-angle direction so as to make the size of the specific object detected thereafter equal to the reference size.

Furthermore, zoom lens units as image taking optical systems being installed in or detachably attached to image pickup apparatuses include a so-called inner focus type lens unit in which a focus lens is disposed further on an image side than a magnification-varying lens (zoom lens). Japanese Patent Laid-Open No. 2005-121752 discloses an inner focus type lens unit that stores plural electronic cams shown inFIG. 9as data, and selects one of the electronic cams corresponding to a detected object distance. Then, this inner focus type lens unit moves the zoom lens and the focus lens so as to trace the selected electronic cam, thereby performing zooming (variation of magnification while maintaining an in-focus state).

As shown inFIG. 9, from a telephoto side to a wide-angle side, the plural electronic cams become converged, in other words, gaps among the plural electronic cams become reduced. Therefore, when the zoom lens is moved from the telephoto side to the wide-angle side, the in-focus state can be easily maintained by the above electronic cam tracing method. However, from the wide-angle side to the telephoto side, the plural electronic cams become diverged. Thus, it may be impossible to determine one electronic cam to be traced, which may make it difficult to maintain the in-focus state or may require a long time to obtain the in-focus state again after falling into an out-of-focus state.

In addition, starting the zoom control by the auto zoom in the out-of-focus state makes it difficult to obtain the in-focus state in the auto zoom.

SUMMARY OF THE INVENTION

The present invention provides an image pickup apparatus capable of avoiding a difficulty of obtaining an in-focus state during the auto zoom.

The present invention provides as an aspect thereof an image pickup apparatus including an image pickup unit configured to photoelectrically convert an object image formed by an image taking optical system, an image production unit configured to produce an image by using an output signal from the image pickup unit, a size detection unit configured to detect a size of a specific object in the image, a storage unit configured to store a target value of the size of the specific object, a zoom control unit configured to perform auto zoom control that automatically provides a specific zoom operation to make the size of the specific object equal or closer to the target value, and a focus control unit configured to perform focus control of the image taking optical system based on a contrast evaluation value obtained from the image. The zoom control unit is configured to restrict the specific zoom operation in the auto zoom control until a determination is made that an in-focus state of the image taking optical system has been obtained by the focus control.

The present invention provides as another aspect thereof an image pickup apparatus including an image pickup unit configured to photoelectrically convert an object image formed by an image taking optical system, an image production unit configured to produce an image by using an output signal from the image pickup unit, a size detection unit configured to detect a size of a specific object in the image, a storage unit configured to store a target value of the size of the specific object, a zoom control unit configured to perform auto zoom control that automatically provides a specific zoom operation to make the size of the specific object equal or closer to the target value, and a focus control unit configured to perform focus control of the image taking optical system based on a contrast evaluation value obtained from the image. The zoom control unit is configured to provide the specific zoom operation in the auto zoom control in response to a determination that an in-focus state of the image taking optical system has been obtained by the focus control.

The present invention provides as still another aspect thereof an image pickup apparatus including an image pickup unit configured to photoelectrically convert an object image formed by an image taking optical system, an image production unit configured to produce an image by using an output signal from the image pickup unit, a size detection unit configured to detect a size of a specific object in the image, a storage unit configured to store a target value of the size of the specific object, a zoom control unit configured to perform auto zoom control that automatically provides a specific zoom operation to make the size of the specific object equal or closer to the target value, and a focus control unit configured to perform focus control of the image taking optical system based on a contrast evaluation value obtained from the image. In the auto zoom control, the focus control unit is configured to make a determination of whether or not an in-focus state has been obtained by the focus control before the specific zoom operation.

The present invention provides as yet still another aspect thereof a method for controlling an image pickup apparatus including an image pickup unit configured to photoelectrically convert an object image formed by an image taking optical system and an image production unit configured to produce an image by using an output signal from the image pickup unit. The method includes a size detection step of detecting a size of a specific object in the image, a storage step of storing a target value of the size of the specific object to a storage unit, a zoom control step of performing auto zoom control that automatically provides a specific zoom operation to make the size of the specific object equal or closer to the target value, and a focus control step of performing focus control of the image taking optical system based on a contrast evaluation value obtained from the image. In the zoom control step, in the auto zoom control, the specific zoom operation is restricted until a determination is made that an in-focus state of the image taking optical system has been obtained by the focus control.

The present invention provides as still further another aspect thereof a method for controlling an image pickup apparatus including an image pickup unit configured to photoelectrically convert an object image formed by an image taking optical system and an image production unit configured to produce an image by using an output signal from the image pickup unit. The method includes a size detection step of detecting a size of a specific object in the image, a storage step of storing a target value of the size of the specific object to a storage unit, a zoom control step of performing auto zoom control that automatically provides a specific zoom operation to make the size of the specific object equal or closer to the target value, and a focus control step of performing focus control of the image taking optical system based on a contrast evaluation value obtained from the image. In the zoom control step, in the auto zoom control, the specific zoom operation is provided in response to a determination that an in-focus state of the image taking optical system has been obtained by the focus control.

The present invention provides as still further another aspect thereof a method for controlling an image pickup apparatus including an image pickup unit configured to photoelectrically convert an object image formed by an image taking optical system and an image production unit configured to produce an image by using an output signal from the image pickup unit. The method includes a size detection step of detecting a size of a specific object in the image, a storage step of storing a target value of the size of the specific object to a storage unit, a zoom control step of performing auto zoom control that automatically provides a specific zoom operation to make the size of the specific object equal or closer to the target value, and a focus control step of performing focus control of the image taking optical system based on a contrast evaluation value obtained from the image. In the focus control step, in the auto zoom control, a determination of whether or not an in-focus state has been obtained is made before the specific zoom operation.

In addition, the present invention provides as yet still further another aspect thereof a computer readable storage medium storing a computer program that causes an image pickup apparatus to perform operations according to any one of the above-described methods.

Other aspects of the present invention will become apparent from the following description and the attached drawings.

DESCRIPTION OF THE EMBODIMENTS

Exemplary embodiments of the present invention will hereinafter be described with reference to the accompanying drawings.

FIG. 1shows the configuration of a video camera as an image pickup apparatus that is a first embodiment (Embodiment 1) of the present invention. Although this embodiment will describe the video camera, alternative embodiments of the present invention include a digital still camera having a video capturing function.

Reference numeral101denotes a first lens unit that is a fixed lens unit, and reference numeral102denotes a second lens unit that moves in an optical axis direction to perform variation of magnification (optical zoom operation). The second lens unit102is hereafter referred to as a “magnification-varying lens”.

Reference numeral103denotes an aperture stop. Reference numeral104denotes a third lens unit that is a fixed lens unit. Reference numeral105denotes a focus compensator lens unit (hereinafter referred to as a “focus lens”) that moves in the optical axis direction to correct image plane variation caused by the variation of magnification and to perform focusing. These lens units101,102,104and105and the aperture stop103constitute an image taking optical system. The image taking optical system in this embodiment is an inner focus type zoom lens unit in which the focus lens105is disposed further on an image side than the magnification-varying lens102.

Reference numeral106denotes an image pickup element as an image pickup unit that is constituted by a photoelectric conversion element such as a CCD sensor or a CMOS sensor and photoelectrically converts an object image formed by the image taking optical system. Reference numeral107denotes a CDS/AGC that performs sampling of an output signal from the image pickup element106to adjust a gain thereof. Reference numeral108denotes a camera signal processing circuit (image production unit) that performs various image processing on an output signal from the CDS/AGC107to produce a video signal (captured image or image data).

Reference numeral109denotes a monitoring device that constitutes a display unit. The monitoring device109displays the video signal (captured image) produced by the camera signal processing circuit108, information showing states of the camera and various warnings. Reference numeral113denotes a recording device that records the video signal (captured image) produced by the camera signal processing circuit108to a recording medium such as an optical disk or a semiconductor memory.

Reference numeral110denotes a zoom motor that is a driving source to move the magnification-varying lens102. Reference numeral111denotes a focus motor that is a driving source to move the focus lens105. These motors110and111are driven in response to a driving instruction from a camera AF microcomputer114to move the corresponding lenses102and105.

Reference numeral112denotes an object detection processing part serving as a size detection unit. The object detection processing part112performs an object detection process described later on the video signal (captured image) to detect an object region in the captured image. Moreover, the object detection processing part112calculates feature amounts of a specific object (that is, a specific object image) included in the object region. The feature amounts include a position and a size (such as a length or an area) of the specific object. The object detection processing part112sends the feature amounts of the specific object to the camera AF microcomputer114.

Methods particularly for detecting a person's face (specific object) in a captured image, which are used in the object detection process, include the following ones as examples:

(1) a method of extracting a skin color region from colors (tones) of pixels constituting the captured image, and detecting the face depending on a matching degree of the skin color region with a face outline plate that is prepared beforehand; and

(2) a method of extracting face feature parts such as eyes, a nose and a mouth from the captured image by using a pattern recognition technology to detect the face.

This embodiment can use any one of the above two methods (1) and (2) in the object detection process, and may use other methods. Moreover, the specific object may be an object other than the person's face. In addition, a method may be used which provides an object specifying unit for enabling a user to specify the specific object and detects an object region including the specific object from luminance information or color information of the specific object in a captured image by using a pattern matching technology.

Reference numeral117denotes an AF evaluation value extraction part. The AF evaluation value extraction part117extracts, from an AF region signal that has passed through an AF gate, a high-frequency component to produce an AF evaluation value signal. The AF gate passes only the AF signal region signal of the video signal (captured image). The AF evaluation value is a contrast evaluation value showing contrast (sharpness) of the video signal (captured image) produced based on the output signal from the image pickup element106. The contrast is changed with a focus state of the image taking optical system, so that the AF evaluation value signal is a signal indicating the focus state of the image taking optical system. The AF evaluation value signal is output to the camera AF microcomputer114.

The camera AF microcomputer114governs control of all operations of the video camera, controls a position of the magnification-varying lens102through auto zoom control, and controls a position of the focus lens105through autofocus control. The camera AF microcomputer114serves as a zoom control unit and a focus control unit. The auto zoom control and the autofocus control are hereinafter simply referred to as “auto zoom” and “autofocus (AF)”, respectively.

Reference numeral115denotes an auto zoom switch that is operated by a user to turn the auto zoom ON (active) and OFF (non-active). The camera AF microcomputer114starts the auto zoom in response to an ON signal from the auto zoom switch115, and ends the auto zoom in response to an OFF signal therefrom.

Reference numeral116denotes a memory (storage unit) that is constituted by a DRAM, a flash ROM or the like, and stores computer programs and data used in various processes performed by the camera AF microcomputer114, the processes including the auto zoom and the autofocus. The memory116also stores data of a reference size as a target value used for keeping a size of the specific object in the auto zoom.

Reference numerals118and119respectively denote a telephoto zoom key and a wide-angle zoom key which constitute a zoom instruction unit. The telephoto and wide-angle zoom keys118and119are operated by the user to instruct variation of magnification (zoom operation) in a telephoto direction and in a wide-angle direction, respectively. The camera AF microcomputer114performs zoom control that moves the magnification-varying lens102in a direction (telephoto or wide-angle direction) corresponding to a zoom instruction signal from an operated one of the telephoto and wide-angle zoom keys118and119. The zoom control in response to the operation of the telephoto and wide-angle zoom keys118and119are hereinafter referred to as “normal zoom (control)”.

Next, description will be made of an AF process performed in a state other than during zoom operations in the auto zoom and normal zoom performed by the camera AF microcomputer114with reference to a flowchart shown inFIG. 3. The camera AF microcomputer114executes this AF process according to the above-described computer program stored in the memory116.

At step301, the camera AF microcomputer (hereinafter simply referred to as a “microcomputer”)114starts the AF process.

At step302, the microcomputer114takes in the AF evaluation value from the AF evaluation value extraction part117.

At step303, the microcomputer114determines whether or not an AF operation mode is a minute drive mode. If the AF operation mode is the minute drive mode, the microcomputer114proceeds to step304and subsequent steps to perform a minute drive process. If the AF operation mode is not the minute drive mode, the microcomputer114proceeds to step310

At step304, the microcomputer114performs minute drive to move the focus lens105alternately in an infinitely-far direction and a close direction with a minute amplitude that generates no visible change in focus state in the captured image. Then, the microcomputer114determines that, of the infinitely-far and close directions, one direction in which the AF evaluation value increases is a direction (hereinafter referred to as an “in-focus direction) in which an in-focus position exists. A detailed description of the minute drive will be made later with reference toFIG. 4.

At step305, the microcomputer114determines whether or not an in-focus counter has reached a predetermined value or more at step304. The in-focus counter will be described later. If a determination (hereinafter referred to as an “in-focus determination”) is made that the image taking optical system is in an in-focus state in response to the predetermined value or more of the in-focus counter, the microcomputer114proceeds to step308to store (hold) the AF evaluation value at the in-focus determination, and then proceeds to step309to enter a restart determination mode. After completion of step309, the microcomputer114returns to step302. On the other hand, if the in-focus determination is not made, the microcomputer114proceeds to step306.

At step306, the microcomputer114determines whether or not the in-focus direction has been determined at step304. If the in-focus direction has been determined, the microcomputer114proceeds to step307to shift the AF operation mode to a climbing drive mode. After completion of step307, the microcomputer114returns to step302. On the other hand, if the in-focus direction has not been determined, the microcomputer114returns to step302to continue the minute drive.

At step310, the microcomputer114determines whether or not the AF operation mode is the climbing drive mode. If the AF operation mode is the climbing drive mode, the microcomputer114proceeds to step311and subsequent steps. If the AF operation mode is not the climbing drive mode, the microcomputer114proceeds to step315.

At step311, the microcomputer114performs the climbing drive to move the focus lens105at a predetermined speed in a direction in which the AF evaluation value increases. A detailed description of the climbing drive will be made later with reference toFIG. 6.

At step312, the microcomputer114determines whether or not the AF evaluation value has exceeded a peak in the climbing drive started at step311. If the AF evaluation value has exceeded the peak, the microcomputer114proceeds to step313. If the AF evaluation value has not exceeded the peak, the microcomputer114returns to step302to continue the climbing drive.

At step313, the microcomputer114sets, in order to return the focus lens105to a peak position at which the AF evaluation value reached the peak in the climbing drive, the peak position to a target lens position.

At step314, the microcomputer114shifts the AF operation mode to a stop mode. After completion of step314, the microcomputer114returns to step302.

At step315, the microcomputer114determines whether or not the AF operation mode is the stop mode. If the AF operation mode is the stop mode, the microcomputer114proceeds to step316and subsequent steps. If the AF operation mode is not the stop mode, the microcomputer114proceeds to step318.

At step316, the microcomputer114determines whether or not the focus lens105has returned to the above-described target lens position. If the focus lens105has returned to the target lens position, the microcomputer114proceeds to step317to shift the AF operation mode to the minute drive mode. After completion of step317, the microcomputer114returns to step302. If the focus lens105has not returned to the target lens position, the microcomputer114returns to step302to continue returning of the focus lens105to the target lens position.

At step318, the microcomputer114compares a current AF evaluation value with the AF evaluation value held at step308to determine whether or not the AF evaluation value has changed by a predetermined amount or more, that is, has significantly changed. If the AF evaluation value has significantly changed, the microcomputer114proceeds to step319to shift the AF operation mode to the minute drive mode. After completion of step309, the microcomputer114returns to step302. If the AF evaluation value has not significantly changed, the microcomputer114returns to step302.

Next, description of the minute drive will be made with reference toFIG. 4. At step401, the microcomputer114starts the process of the minute drive. At step402, the microcomputer114determines whether or not a current minute drive mode is 0. If the minute drive mode is 0, the microcomputer114proceeds to step403for a case where the focus lens105is located on a close side. If the minute drive mode is not 0, the microcomputer114proceeds to step407.

At step403, the microcomputer114first stores (holds) the AF evaluation value as a process for the case where the focus lens105is located on the close side. The AF evaluation value held here has been obtained from the video signal produced by using electrical charges accumulated in the image pickup element106when the focus lens105is located on an infinitely-far side at step415described later. After completion of step403, the microcomputer114proceeds to step404.

At step407, the microcomputer114determines whether or not the current minute drive mode is 1. If the minute drive mode is 1, the microcomputer114proceeds to step408and subsequent steps for the case where the focus lens105is located on the infinitely-far side. If the minute drive mode is not 1, the microcomputer114proceeds to step414.

At step408, the microcomputer114compares the AF evaluation value on the infinitely-far side held at step403with the AF evaluation value on the close side held at step415described later. If the AF evaluation value on the infinitely-far side is larger than the AF evaluation value on the close side, the microcomputer114proceeds to step409. If the AF evaluation value on the close side is larger than the AF evaluation value on the infinitely-far side, the microcomputer114proceeds to step412.

At step409, the microcomputer114calculates a drive amplitude (modulation amplitude) by adding a center movement amplitude to a vibration amplitude. The center movement amplitude is a movement amount of a vibration center which will be described later.

At step412, the microcomputer114sets the vibration amplitude to the drive amplitude. These drive amplitudes are set within a depth of focus.

At step410, the microcomputer114determines whether or not a drive direction (correction direction) of the focus lens105has been reversed to a previous drive direction. If the correction direction has been reversed, the microcomputer114proceeds to step411to increase the in-focus counter by one, and then proceeds to step413. If the correction direction has not been reversed, the microcomputer114directly proceeds to step413.

At step413, the microcomputer114moves the focus lens105in the infinitely-far direction by the drive amplitude set at step409or step412. Then, the microcomputer114proceeds to step404.

At step414, the microcomputer114determines whether or not the current minute drive mode is 2. If the minute drive mode is 2, the microcomputer114proceeds to step415for the case where the focus lens105is located on the infinitely-far side. If the minute drive mode is not 2, the microcomputer114proceeds to step416.

At step415, the microcomputer114stores (holds) the AF evaluation value as a process for the case where the focus lens105is located on the infinitely-far side. The AF evaluation value held here has been obtained from the video signal produced by using electrical charges accumulated in the image pickup element106when the focus lens105is located on the close side at step403. After completion of step415, the microcomputer114proceeds to step404.

At step416, the microcomputer114compares the AF evaluation value on the close side held at step415with the AF evaluation value on the infinitely-far side held at step403. If the AF evaluation value on the close side is larger than the AF evaluation value on the infinitely-far side, the microcomputer114proceeds to step417. If the AF evaluation value on the infinitely-far side is larger than the AF evaluation value on the close side, the microcomputer114proceeds to step420.

At step417, the microcomputer114calculates the drive amplitude by adding the vibration amplitude to the center movement amplitude.

At step418, the microcomputer114sets the vibration amplitude to the drive amplitude. These drive amplitudes are set within the depth of focus.

At step418, the microcomputer114determines whether or not the drive direction (correction direction) of the focus lens105has been reversed to the previous drive direction. If the correction direction has been reversed, the microcomputer114proceeds to step419to increase the in-focus counter by one, and then proceeds to step421. If the correction direction has not been reversed, the microcomputer114directly proceeds to step421.

At step421, the microcomputer114moves the focus lens105in the close direction by the drive amplitude set at step417or step420. Then, the microcomputer114proceeds to step404. Thus, reciprocating movement of the focus lens105in the infinitely-far and close directions is repeated in a predetermined movement range in response to changes of the AF evaluation value, and thereby the value of the in-focus counter is increased every movement.

At step404, if the current minute drive mode is 3, the microcomputer114changes it to 0. If the minute drive mode is not 3, the microcomputer114increases the minute drive mode by 1, and then proceeds to step405.

At step405, the microcomputer114clears the in-focus counter in response to situations, for example, a case where a determination has been made that the AF evaluation value has been significantly changed due to a change of an object state and a case where the focus lens105has been moved out of the predetermined movement range. Then, the microcomputer114proceeds to step406to end the process.

FIG. 5Ashows the movement of the focus lens105in the AF process. The upper part ofFIG. 5Ashows a vertical synchronization signal of the video signal. A horizontal axis inFIG. 5Ashows time, and a vertical axis therein shows the position of the focus lens105(hereinafter referred to as a “focus lens position”).

An AF evaluation value EVAobtained from the video signal produced by using electric charges accumulated in the image pickup element106during a time period labeled with A is taken into the microcomputer114at a time TA. An AF evaluation value EVBobtained from the video signal produced by using electric charges accumulated in the image pickup element106during a time period labeled with B is taken into the microcomputer114at a time TB. At a time TC, the microcomputer114compares the AF evaluation value EVAwith the AF evaluation value EVB, and moves the above-described vibration center only when EVBis larger than EVA. Moving the vibration center to a direction in which the AF evaluation value increases enables searching for an in-focus position. A movement amount of the focus lens105here is set, based on the depth of focus, to a movement amount that generates no visible change in focus state in the captured image.

Next, description of the climbing drive will be made with reference toFIG. 6. At step601, the microcomputer114starts the process of the climbing drive. At step602, the microcomputer114determines whether or not the AF evaluation value currently obtained is larger than the AF evaluation value previously obtained. If the current AF evaluation value is larger than the previous AF evaluation value, the microcomputer114proceeds to step603. If the current AF evaluation value is smaller than the previous AF evaluation value, the microcomputer114proceeds to step605.

At step603, the microcomputer114moves the focus lens105at a predetermined speed in a same direction (forward direction) as that of a previous movement, and then proceeds to step604to end this process.

At step605, the microcomputer114determines whether or not the AF evaluation value has exceeded its peak and has then decreased. If the AF evaluation value has not exceeded the peak, the microcomputer114proceeds to step606. If the AF evaluation value has exceeded the peak and has then decreased, the microcomputer114proceeds to step604to end this process and then shifts to the minute drive.

At step606, the microcomputer114moves the focus lens105at the predetermined speed in a reverse direction to that at the previous movement, and then proceeds to step604to end this process.

FIG. 7shows movements of the focus lens105by the climbing drive. In a movement A, the AF evaluation value exceeds its peak and then decreases, so that the microcomputer114determines that an in-focus position exists within the movement A, and then ends the climbing drive to shift to the minute drive. On the other hand, in a movement B, the AF evaluation value decreases without a peak, so that the microcomputer114determines that it has mistaken the in-focus direction and therefore reverses the drive direction of the focus lens105to continue the climbing drive.

As described above, the microcomputer114controls the position of the focus lens105to maintain an in-focus state such that the AF evaluation value always becomes maximum while repeating “minute drive”→“climbing drive”→“stop”→“minute drive”→“restart determination”→“minute drive”.

Next, a detailed description of an AF process performed during the zoom operation by the microcomputer114will be made. First, description will be made of an example of a focus lens electronic cam tracing control method with reference toFIG. 8A. InFIG. 8A, Z0, Z1, Z2, . . . , Z6show positions of the magnification varying lens (hereinafter also referred to as a “zoom lens”)102. Moreover, a0, a1, a2, . . . , a6and b0, b1, b2, . . . , b5show positions of the focus lens105corresponding to two object distances prestored in the microcomputer114. Each of groups of these focus lens positions (a group of a0, a1, a2, . . . , a6and a group b0, b1, b2, . . . , b6) is a representative in-focus cam that is an electronic cam to be traced by the focus lens105in order to maintain an in-focus state at each representative object distance.

Furthermore, p0, p1, p2, . . . , p6are positions on a virtual in-focus cam to be traced by the focus lens105, the virtual in-focus cam being calculated based on the above-described two representative in-focus cams. The position on the virtual in-focus cam is calculated by using the following expression:
pn+1=|pn−an|/|bn−an|×bn+1−an+1|+an+1(1)

With the above expression (1), when for example the focus lens105is located at p0inFIG. 8A, a ratio (internal division ratio) at which p0internally divides a line segment b0−a0is calculated, and a point that internally divides a line segment b1−a1according to this ratio is defined as p1. Then, from a difference p1−p0between the positions p0and p1and from a time required for the zoom lens102to be moved from Z0to Z1, a movement speed of the focus lens105in order to maintain the in-focus state is calculated.

Next, description will be made of a case where a stop position of the zoom lens102is not restricted to positions located on boundaries of zoom areas, the representative in-focus cam data being provided on the boundaries.FIG. 8Bshows a focus lens position interpolation calculation method, wherein part ofFIG. 8Ais extracted and the zoom lens102is located at an arbitrary position. InFIG. 8B, a vertical axis shows the position of focus lens105(focus lens position) and a horizontal axis shows the position of the zoom lens102(hereinafter referred to as a “zoom lens position”). When the zoom lens positions are shown by Z0, Z1, . . . , Zk−1, Zk, . . . , Zn, the focus lens positions on the representative in-focus cams for two representative object distances, which are stored in the microcomputer114, are shown by a0, a1, . . . , ak−1, ak, . . . , anand b0, b1, . . . , bk−1, bk, . . . , bn.

In a case where the zoom lens position is Zx, which is not on the boundary of the zoom area, and the focus lens position is Px, axand bxare calculated as follows:
ax=ak−(Zk−Zx)(ak−ak−1)/(Zk−Zk−1)  (2)
bx=bk−(Zk−Zx)(bk−bk−1)/(Zk−Zk−1)  (3)

In other words, the internal division ratio is calculated from a current zoom lens position and positions of two zoom area boundaries (for example, Zkand Zk−1inFIG. 8B) located on both sides of the current zoom lens position. Then, axand bxcan be calculated by internally dividing two positions corresponding to a same object distance among the prestored four focus lens positions on the representative in-focus cams (ak, ak−1, bkand bk−1inFIG. 8B) with the above-described internal division ratio.

In addition, according to the internal division ratio obtained from ax, pxand bx, pkand pk−1can be calculated by internally dividing two positions corresponding to a same focal length among the prestored four focus lens positions on the representative in-focus cams with the above-described internal division ratio, as shown by the expression (1).

When zooming from the wide-angle side to the telephoto side is performed, the movement speed of the focus lens105to maintain an in-focus state is calculated from the difference between the focus lens position pkthat is a tracing destination and the current focus lens position px, and from the time required for the zoom lens102to be moved from Zxto Zk. Further, when zooming from the telephoto side to the wide-angle side is performed, the movement speed of the focus lens105to maintain an in-focus state is calculated from the difference between the focus lens position pk−1that is a tracing destination and the current focus lens position px, and from the time required for the zoom lens102to be moved from Zxto Zk−1.

FIG. 8Cshows an example of table data of the representative in-focus cams prestored in the microcomputer114.FIG. 8Cshows in-focus position (focus lens position) data A(n,v) for each object distance, the data changing with the zoom lens position. The object distance shown by a variable n changes in a horizontal (column) direction, and the zoom lens position (focal length) shown by a variable v changes in a vertical (low) direction. In this table, n=0 denotes an infinitely-far object distance, and the object distance changes to the close side as n increases. For, example, n=m denotes an object distance of 1 cm.

On the other hand, v=0 denotes a wide-angle end. In addition, the focal length increases as v increases, and v=s denotes a telephoto end. Therefore, one representative in-focus cam is drawn by the table data in one low. In other words, with the movement of the zoom lens102, selecting one electronic cam corresponding to the object distance among the plural electronic cams shown inFIG. 9so as to move the focus lens105according to the selected electronic cam by the above-described method enables a zoom operation while maintaining an in-focus state, that is, zooming.

However, as described above, when the zoom lens102is moved from the wide-angle side to the telephoto side, one electronic cam to be traced by the focus lens105among the plural electronic cams cannot be determined since the plural electronic cams are mutually converged on the wide-angle side, and therefore it may be impossible to maintain an in-focus state.

Thus, as shown inFIG. 5B, in the above-described in-focus cam tracing control during the zoom operation, this embodiment repeatedly updates the vibration center of the minute drive of the focus lens105in response to increase and decrease of the AF evaluation value to specify one electronic cam to be traced by the focus lens105. Such drive control of the focus lens105is referred to as “modulation operation” of the focus lens105.

The upper part ofFIG. 5Bshows a vertical synchronization signal of the video signal as well asFIG. 5A. InFIG. 5B, a horizontal axis shows time, and a vertical axis shows the focus lens position. In the modulation operation of the focus lens105in the zoom operation, the vibration center is located on one in-focus cam to be traced by the focus lens105(hereinafter referred to as a “reference cam”), and a gradient of the vibration center is changed depending on the object distance corresponding to the reference cam to be traced and the zoom lens position.FIG. 5Bshows a case where the modulation operation is repeatedly performed in a cycle of four vertical synchronization times (4V). The modulation operation includes the following four operation steps.

When a counter of the operation step of the modulation operation is 0, the focus lens105is moved so as to keep a relative positional relationship between the position of the focus lens105obtained when the counter is 3 and the vibration center. When the counter is 1, a position away from the vibration center to the infinitely-far side by the vibration amplitude is set to a target position, and the focus lens105is moved to the target position.

When the counter is 2, the focus lens105is moved so as to keep a relative positional relationship between the position of the focus lens105obtained when the counter is 1 and the vibration center. When the counter is 3, a position away from the vibration center to the close side by the vibration amplitude is set to a target position, and the focus lens105is moved to the target position. The cycle of the modulation operation is not limited to 4V, and may be a cycle corresponding to an integral multiple of 2V, such as 2V and 8V.

As well asFIG. 5A, the AF evaluation value EVAobtained from the video signal produced by using the electric charges accumulated in the image pickup element106during the time period labeled with A is taken into the microcomputer114at the time TA. Moreover, the AF evaluation value EVBobtained from the video signal produced by using the electric charges accumulated in the image pickup element106during the time period labeled with B is taken into the microcomputer114at the time TB. At the time TC, the microcomputer114compares the AF evaluation value EVAwith the AF evaluation value EVB, and moves the vibration center only when EVBis larger than EVA.

As described above, in the zoom operation, moving the vibration center so as to increase the AF evaluation value by using a combination of the reference cam tracing control based on the in-focus cam data and the modulation operation of the focus lens105makes it possible to correctly specify the in-focus cam to be traced. The movement amount of the focus lens105here is set based on the depth of focus to a movement amount that generates no visible defocus in the captured image.

Next, a detailed description will be made of the auto zoom performed by the microcomputer114with reference toFIG. 2. The auto zoom is also executed according to a computer program stored in the memory116.

At step201, the microcomputer114starts the process of the auto zoom. At step202, the microcomputer114determines whether or not the zoom operation of the image taking optical system is currently performed. This is to perform the above-described AF control in which the in-focus cam tracing control is combined with the modulation operation in the zoom operation, which is different from a case where the zoom operation is not performed. If the zoom operation is not currently performed, the microcomputer114proceeds to step203. If the zoom operation is currently performed, the microcomputer114directly proceeds to step204.

At step203, the microcomputer114performs the AF control to search for the in-focus position based on the AF evaluation value while moving the focus lens105.

At step204, the microcomputer114causes the object detection processing part112to detect a face, which is the specific object, and stores the size S of the face in the memory116.

At step205, the microcomputer114determines whether or not the auto zoom is currently performed. If the auto zoom is not currently performed, the microcomputer114proceeds to step206. If the auto zoom is currently performed, the microcomputer114proceeds to step208.

At step206, the microcomputer114determines whether or not the auto zoom switch115has been turned ON by a user. If the auto zoom switch115has not been turned ON, the microcomputer114proceeds to step220to perform the normal zoom in response to operations of the zoom keys118and119, and then returns to step202. On the other hand, if the auto zoom switch115has been turned ON, the microcomputer114proceeds to step207to store the current size S of the face as the reference size S0, which is the target value of the auto zoom, in the memory116.

At step208, the microcomputer114determines whether or not the auto zoom switch115has been turned OFF by the user. If the auto zoom switch115has been turned OFF, the microcomputer114proceeds to step221to stop the zoom operation, and then returns to step202. On the other hand, if the auto zoom switch115has not been turned OFF, the microcomputer114proceeds to step209.

At step209, the microcomputer114stores an absolute value of a difference between the current size S of the face and the reference size S0as a variable DIFF. Then, the microcomputer114proceeds to step210to determine whether or not the variable DIFF is larger than a predetermined value (hereinafter referred to as a “threshold”) TH. The threshold TH is provided for preventing the zoom lens102being continuously and minutely moved by the auto zoom when the size S of the object is minutely changed due to detection errors in the object detection processing part112or the like. That is, the threshold TH is provided for allowing the auto zoom to be activated when the difference between the current size S of the object and the reference size S0increases to some extent.

The threshold TH may be a fixed value, and may be defined as a ratio to the size S of the object, such as 10% of the size S. Moreover, the threshold TH may be changed depending on a zoom magnification.

If determining at step210that the variable DIFF, which is the difference between the current size S of the face and the reference size S0, is smaller than the threshold TH, the microcomputer114proceeds to step221to stop the zoom operation, and then returns to step202.

On the other hand, if determining that the difference (variable) DIFF is larger than the threshold TH, the microcomputer114proceeds to step211to determine whether or not the current size S of the face is larger than the reference size S0. If the current size S is larger than the reference size S0, the microcomputer114proceeds to step212to determine whether or not the zoom operation in the auto zoom is currently stopped. If the zoom operation is currently stopped, the microcomputer114proceeds to step213. If the zoom operation is not currently stopped, the microcomputer114proceeds to step214.

At step213, the microcomputer114determines whether or not the in-focus counter is larger than a predetermined value th2, in other words, whether or not an in-focus state has been obtained. If determining that the in-focus counter is larger than the predetermined value th2(that is, the in-focus determination is made) while the zoom operation is stopped, the microcomputer114proceeds to step214to start the zoom operation in the auto zoom in the wide-angle direction, and then returns to step202. In other words, this embodiment restricts, as a general rule, the zoom operation in the auto zoom until the in-focus determination is made in the AF, and releases the restriction of the zoom operation in the auto zoom, that is, allows start thereof in response to the in-focus determination.

Although this embodiment describes the case where the restriction of the zoom operation restricts the start of the zoom operation to disable the entire zoom operation, the restriction of the zoom operation is not limited thereto. For example, the restriction of the zoom operation may include restriction of a lens movable range for the zoom operation and restriction a lens movement speed in the zoom operation. In these cases, until the in-focus determination is made, the lens movable range may be set to be narrower and the lens movement speed may be set to be slower than those before the restriction is made.

On the other hand, when directly proceeding to step214due to a determination that the zoom operation in the auto zoom is not currently stopped at step212, the microcomputer114continues the auto zoom in the wide-angle direction.

Moreover, if determining that the in-focus counter is smaller than the predetermined value th2at step213(that is, the in-focus determination cannot be made), the microcomputer114proceeds to step215to determine whether or not that situation has continued for a predetermined time. If an in-focus state is not obtained even though the predetermined time has elapsed, since the object may be an object on which no in-focus state can be obtained, the microcomputer114proceeds to step214to start the zoom operation in the auto zoom in the wide-angle direction. If the situation where the in-focus determination cannot be made has not yet continued for the predetermined time, the microcomputer114proceeds to step221to keep the zoom operation stopped.

Thus, this embodiment releases, as an exception to the general rule, the restriction of the zoom operation in the auto zoom in the wide-angle direction, that is, allows the start thereof, when that restriction has continued for more than the predetermined time, even though no in-focus determination is made.

On the other hand, if determining that the current size S is smaller than the reference size S0at step211, the microcomputer114proceeds to step216to determine whether or not the zoom operation in the auto zoom is currently stopped. If determining that the zoom operation in the auto zoom is currently stopped, the microcomputer114proceeds to step217to determine whether or not the in-focus counter is larger than a predetermined value th1, in other words, whether or not an in-focus state has been obtained. Then, if determining that the in-focus counter is larger than the predetermined value th1(that is, the in-focus determination is made) while the zoom operation is currently stopped, the microcomputer114proceeds to step218to start the zoom operation in the auto zoom in the telephoto direction, and then returns to step202. In other words, as well as in the above-described auto zoom in the wide-angle direction, also in the auto zoom in the telephoto direction, as a general rule, this embodiment restricts the zoom operation until the in-focus determination is made in the AF, and releases the restriction of the zoom operation, that is, allows start thereof in response to the in-focus determination.

When directly proceeding to step218due to a determination that the zoom operation in the auto zoom is not currently stopped at step216, the microcomputer114continues the auto zoom in the telephoto direction.

Moreover, if determining that the in-focus counter is smaller than the predetermined value th1(that is, the in-focus determination cannot be made) at step217, the microcomputer114proceeds to step219to determine whether or not that situation has continued for the predetermined time. If the in-focus state is not obtained even though the predetermined time has elapsed, since the object may be an object on which no in-focus state can be obtained, the microcomputer114proceeds to step218to start the zoom operation in the auto zoom in the telephoto direction. If the situation where the in-focus determination cannot be made has not yet continued for the predetermined time, the microcomputer114proceeds to step221to keep the zoom operation stopped.

Thus, also in the auto zoom in the telephoto direction, this embodiment releases, as an exception to the general rule, the restriction of the zoom operation, that is, allows the start thereof when that restriction has continued for more than the predetermined time, even though no in-focus determination is made.

Next, description will be made of the relationship between the predetermined values th1and th2. In the inner focus type zoom lens unit, even though an in-focus state is not obtained on the telephoto side, a zoom operation to the wide-angle side brings the zoom lens unit into a near in-focus state. Therefore, this embodiment sets the predetermined value th2that is a threshold for the in-focus determination in the wide-angle direction to a small value or 0 so as to allow the zoom operation in the auto zoom even if a certain in-focus state may not be actually obtained. On the other hand, this embodiment sets the predetermined value th1that is a threshold for the in-focus determination in the telephoto direction to a value larger than the predetermined value th2so as to allow the zoom operation in the auto zoom after a certain in-focus state is obtained in order to enable maintaining of the in-focus state during the auto zoom. Thus, the predetermined values th1and th2satisfy the following relationship:
th2<th1.

In particular, in a case where the predetermined value th2is set to 0, the in-focus determination is made when the zoom operation is performed on the telephoto side, but the in-focus determination is not substantially made when the zoom operation is performed on the wide-angle side. This case corresponding to a case where steps212,213and215are omitted from the flowchart shown inFIG. 2.

Setting the predetermined value th2to a small value makes it possible to prevent the start of the zoom operation in the auto zoom from being delayed more than necessary.

The above-described auto zoom performs the zoom operation so as to make the size of the specific object equal or closer to the reference size (target value). The size close (closer) to the reference size means that, for example, the size is included within a range having a slight difference from the reference size.

Next, description will be made of an AF process performed during the zoom operation by the microcomputer114with reference to a flowchart shown inFIG. 10. This AF process is executed at steps214and218in the flowchart shown inFIG. 2.

At step1001, the microcomputer114starts the process of the AF. At step1002, the microcomputer114determines whether or not the zoom operation is currently performed. If the zoom operation is currently performed, the microcomputer114proceeds to step1003. If the zoom operation is not currently performed, the microcomputer114proceeds to step1023to end this process.

At step1003, the microcomputer114sets a drive speed Zsp of the zoom motor110, and then proceeds to step1004.

At step1004, the microcomputer114estimates a distance to an object (object distance) whose image is to be captured, from the current positions of the zoom lens102and the focus lens105. Then, the microcomputer114stores information on the object distance in a memory area such as a RAM, as three cam parameters (data for obtaining a target position) α, β and γ. At this step, a process shown inFIG. 11is performed. In order for simplification, description of the process shown inFIG. 11will be made as if an in-focus state is maintained at the current zoom and focus lens positions.

At step1101inFIG. 11, the microcomputer114calculates which zoom area (v) among plural (s) zoom areas on the table data shown inFIG. 8Cthe current zoom position Zxis included in. The plural zoom areas are formed by equally dividing an entire zoom range from the wide-angle end to the telephoto end into s segments. The calculation method will be described with reference toFIG. 12.

At step1201inFIG. 12, the microcomputer114clears a zoom area variable v. At step1202, the microcomputer114calculates a zoom lens position Z(v) on the boundary of the zoom area v according to the following expression (4). This Z(v) corresponds to the zoom lens positions Z0, Z1, Z2, . . . , shown inFIG. 8A.
Z(v)=(D−E)×v/s+E(4)
where D represents the zoom lens position at the telephoto end, and E represents the zoom lens position at the wide-angle end.

At step1203, the microcomputer114determines whether or not Z(v) calculated at step1202is equal to the current zoom lens position Zx. If Z(v) is equal to the current zoom lens position Zx, the microcomputer114proceeds to step1207to regard that the current zoom lens position Zxis located on the boundary of the zoom area v, and therefore to set 1 to a boundary flag. Then, the microcomputer114proceeds to step1102shown inFIG. 11.

On the other hand, if Z(v) is not equal to the current zoom lens position Zxat step1203, the microcomputer114proceeds to step1204to determine whether or not Zx<Z(v), that is, whether or not the current zoom lens position Zxis closer to the wide-angle end than the zoom area Z(v). If Zx<Z(v), the microcomputer114proceeds to step1206to regard that the current zoom lens position Zxis located between Z(v−1) and Z(v), and therefore to set 0 to the boundary flag. Then, the microcomputer114proceeds to step1102shown inFIG. 11. If not Zx<Z(v), the microcomputer114proceeds to step1205to shift the zoom area v by +1, and then returns to step1202.

Repeating the process ofFIG. 12can provide, at the time of completing the repeated processes, information on whether or not the current zoom lens position Zxis included in the v(=k)-th zoom area (hereinafter referred to as a “current zoom area”) on the data table shown inFIG. 8Cand information on whether or not Zxis located on the boundary of the zoom area.

Returning to the flowchart shown inFIG. 11, since the current zoom area has been determined by the process shown inFIG. 12at step1101, the microcomputer114calculates which focus area among plural focus areas on the table data shown inFIG. 8Cthe current focus position is included in.

First at step1102, the microcomputer114clears an object distance variable n. Next at step1103, the microcomputer114determines whether or not the current zoom lens position is located on the boundary of the zoom area, that is, whether or not the boundary flag is set to 1. If the boundary flag is 0, the microcomputer114regards that the current zoom lens position is not located on the boundary to proceed to processes from step1105. If the boundary flag is 1, the microcomputer114regards that the current zoom lens position is located on the boundary to proceed to processes from step1104.

At step1105, the microcomputer114sets Z(v) to Zkand sets Z(v−1) to Zk−1. Next, at step1106, the microcomputer114retrieves, from the table data shown inFIG. 8C, four in-focus position data A(n,v−1), A(n,v), A(n+1,v−1) and A(n+1,v). Then, at step1107, the microcomputer114calculates axand bxby using the above-described expressions (2) and (3).

On the other hand, at step1104, the microcomputer114retrieves, from the table data, two in-focus position data A(n,v) and A(n+1,v) for the zoom lens position v at the object distances n and n+1. Then, the microcomputer114stores A(n,v) and A(n+1,v) as axand bx, respectively.

At step1108, the microcomputer114determines whether or not the current focus lens position pxis equal to or greater than ax, that is, whether or not the current focus lens position pxis equal or closer to a close end than ax. If pxis equal to or greater than ax, the microcomputer114proceeds to step1109to determine whether or not the current focus lens position pxis equal to or greater than bx, that is, whether or not the current focus lens position pxis equal or closer to the close end than bx. If pxis not equal to or greater than bx, that is, the current focus lens position pxis located between the in-focus positions corresponding to the object distances n and n+1, the microcomputer114stores the cam parameters for this situation in the memory area at steps1113to1115. Specifically, the microcomputer114sets α=px−axat step1113, sets β=bx−axat step1114, and sets γ=n at step1115. Then, the microcomputer114proceeds from step1115to step1005shown inFIG. 10.

If determining that pxis not equal to or greater than axat step1108, the current focus lens position pxis located at a position exceeding an infinitely-far end. In this case, the microcomputer114proceeds to step1112to set α=0, and then proceeds to processes from step1114to store the cam parameters for the infinitely-far end.

If determining that pxis equal to or greater than bxat step1109, the current focus lens position pxis located further on the close side than bx. In this case, the microcomputer114proceeds to step1110to increase the object distance n by 1, and then proceeds to step1111to determine whether or not the object distance n is further on the infinitely-far side than a closest object distance m. If the object distance n is further on the infinitely-far side than the closest object distance m, the microcomputer114returns to step1103. If the object distance n is not further on the infinitely-far side than the closest object distance m, the current focus lens position pxis located at a position exceeding the close end. In this case, the microcomputer114proceeds to step1112to store the cam parameters for the close end. Specifically, the microcomputer114sets α=0 at step1112, sets β=bx−axat step1114, and sets γ=n at step1115. Then, the microcomputer114proceeds from step1115to step1005shown inFIG. 10.

Returning toFIG. 10, as described above, the microcomputer114at step1004stored the cam parameters showing which in-focus cam among the plural in-focus cams shown inFIG. 9the current zoom lens position and the current focus lens position are located on. Next at step1005, the microcomputer114calculates a position Zx′ that is a destination position at which the zoom lens102will arrive from the current position Zxafter one vertical synchronization time (1V). Then, the microcomputer114proceeds to step1006.

When the zoom speed decided at step1003is denoted by Zsp (pps), the zoom lens position Zx′ after 1V is given by the following expression (5). In the expression (5), pps represents a unit showing a rotational speed of a stepping motor as the zoom motor110, which shows a rotation step amount per one second (one step corresponds to one pulse). Moreover, signs (+ and −) in the expression (5) indicate the movement direction of the zoom lens102, + indicating the telephoto direction and − indicating the wide-angle direction,
Zx′=Zx±Zsp/vertical synchronization frequency.  (5)

Next, at step1006, the microcomputer114calculates a focus lens position px′ on the reference cam for the zoom lens position Zx′ from the cam parameters α, β and γ stored at step1004and from the in-focus position data (table data). Then, the microcomputer114proceeds to step1007. Description will hereinafter be made of the calculation of the focus lens position px′ with reference toFIG. 13.

At step1301ofFIG. 13, the microcomputer114calculates which zoom area v′ the zoom lens position Zx′ is included in. At step1301, the microcomputer114performs processes similar to those shown inFIG. 12. Specifically, the microcomputer114performs the processes shown inFIG. 11using Zx′ instead of Zxand using v′ instead of v.

Next at step1302, the microcomputer114determines whether or not the zoom lens position Zx′ after 1V is located on the boundary of the zoom area, in other words, whether or not the boundary flag is set to 1. If the boundary flag is set to 0, the microcomputer114regards that the zoom lens position Zx′ is not located on the boundary to proceed to process from step1303. If the boundary flag is set to 1, the microcomputer114regards that the zoom lens position Z40′ is located on the boundary to proceed to step1306.

Next, at step1304, the microcomputer114retrieves from the data table shown inFIG. 8Cfour in-focus position data A(γ,v′−1), A(γ,v′), A(γ+1,v′−1) and A(γ+1,v′) in which the object distance γ is specified by the process shown inFIG. 11. Then, at step1305, the microcomputer114calculates ax′ and bx′ by using the above-described expressions (2) and (3). The microcomputer114thereafter proceeds to step1307.

On the other hand, at step1306, the microcomputer114retrieves from the data table two in-focus position data A(γ,v′) and A(γ+1,v′) for the object distances γ and γ+1 in the zoom area v′, and then stores A(γ,v′) and A(γ+1,v′) in the memory area as ax′ and bx′, respectively.

At step1307, the microcomputer114calculates an in-focus position (target focus lens position) px′ of the focus lens105for the zoom lens position Zx′ after 1V. By using the expression (1), the target focus lens position px′ after 1V can be expressed as the following expression (6):
px′=(bx′−ax′)×α/β+ax′.  (6)

Accordingly, a difference ΔF between the target focus lens position px′ and the current focus lens position pxis shown by the following expression:
ΔF=(bx′−ax′)×α/β+ax′−px.

A drive speed of the focus lens105can be obtained by dividing the focus lens position difference ΔF by a movement time of the zoom lens102required to be moved by a distance corresponding to ΔF. When the zoom lens102is driven from the wide-angle side to the telephoto side at a fixed (constant) speed, the drive speed of the focus lens105can be regarded as same as a gradient of the cam shown inFIG. 9. Therefore, the drive speed of the focus lens105increases as the zoom lens position becomes closer to the telephoto end and as the object distance becomes closer to an infinitely far distance.

Returning toFIG. 10, at step1007, the microcomputer114sets the vibration amplitude M and the center movement amplitude W in the above-described modulation operation, on the basis of information on the depth of focus at the zoom lens position Zx′ and the like. Then, the microcomputer114proceeds to step1008.

At step1008, the microcomputer114determines whether or not the auto zoom is currently performed. If the auto zoom is currently performed, the microcomputer114proceeds to step1009. If the auto zoom is not currently performed, the microcomputer114proceeds to step1010.

At step1009, the microcomputer114multiplies the center movement amplitude W by a coefficient c smaller than 1 to decrease the center movement amplitude W, in order to stably perform the AF control in the zoom operation with a small center movement amplitude W. Then, the microcomputer114proceeds to step1010.

At step1010, the microcomputer114determines whether or not a current mode of the modulation operation is 0. If the mode is 0, the microcomputer114proceeds to step1011. If the mode is not 0, the microcomputer114proceeds to step1012.

At step1011, the microcomputer114sets a drive target position Fx′ of the focus lens105after 1V as follows so as to keep a relative positional relationship between the current focus lens position and the reference cam,
Fx′=px′+M.

At step1012, the microcomputer114determines whether or not the current mode of the modulation operation is 1. If the mode is 1, the microcomputer114proceeds to step1013. If the mode is not 1, the microcomputer114proceeds to step1014.

At step1013, the microcomputer114sets the drive target position Fx′ of the focus lens105after 1V as follows such that a position where the modulation amplitude (drive amplitude) (M+W) is superimposed on px′ in the infinitely-far direction becomes the drive target position Fx′,
Fx′=px′−(M+W).

At step1014, the microcomputer114determines whether or not the current mode of the modulation operation is 2. If the mode is 2, the microcomputer114proceeds to step1015. If the mode is not 2, the microcomputer114proceeds to step1016.

At step1015, the microcomputer114sets the drive target position Fx′ of the focus lens105after 1V as follows so as to keep the relative positional relationship between the current focus lens position and the reference cam,
Fx′=px′−M.

At step1016, the microcomputer114sets the drive target position Fx′ of the focus lens105after 1V as follows such that a position where the modulation amplitude (M+W) is superimposed on px′ in the close direction becomes the drive target position Fx′,
Fx′=px′+(M+W).

At step1017, the microcomputer114calculates the drive speed (focus drive speed) Fsp when moving the focus lens105to the drive target position Fx′ set at step1011,1013,1015or1016. The focus drive speed Fsp can be obtained by dividing a difference between the drive target position Fx′ on which the modulation amplitude (M+W) has been superimposed and the current focus lens position pxby a movement time of the zoom lens102required to be moved by a distance corresponding to the above positional difference.

This embodiment sets the movement time of the zoom lens102to a same time as one vertical synchronization time because this embodiment also moves the zoom lens102in synchronization with the vertical synchronization time. In other words, the focus drive speed Fsp is calculated by the following expression:
Fsp=|Fx′−px|/one vertical synchronization time.

At step1018, the microcomputer114shifts the mode to 0 if the current mode is 3 or increases the mode by 1 if the current mode is not 3, and then proceeds to step1019.

At step1019, the microcomputer114produces driving signals on the basis of the target positions and the drive speeds of the zoom lens102and the focus lens105calculated in the above-described processes, and controls the zoom motor110and the focus motor111by supplying the driving signals thereto to move the zoom lens102and the focus lens105. Then, the microcomputer114proceeds to step1020to end the process.

Thus, in the auto zoom that is started after the in-focus determination is made, the center movement amplitude W is set to be smaller than that in the normal zoom. That is, the focus drive speed in the image taking optical system during the auto zoom is made to be slower than that during the normal zoom. This speed setting can prevent the focus lens105from significantly deviating from the in-focus cam even if the focus lens105is moved in a wrong direction by the autofocus.

The above-described embodiment waits for the in-focus determination before the start of the zoom operation in the auto zoom, which makes it easy to obtain and maintain an in-focus state during the zoom operation in the auto zoom. Therefore, generation of defocus during the zoom operation in the auto zoom can be prevented.

Moreover, the above-described embodiment changes the condition for the in-focus determination (that is, the condition for determining whether or not the in-focus state has been obtained) depending on the zoom direction, which can prevent the zoom operation in the auto zoom from becoming slow due to needless waiting for the in-focus determination.

Although the above embodiment described the case of performing the auto zoom by using the optical zoom operation, the auto zoom may be performed by electronic zoom operation that enlarges part of the captured image. Moreover, the auto zoom may be performed by a combination of the optical zoom operation and the electronic zoom operation. In other words, embodiments of the present invention include image pickup apparatuses capable of performing at least one of the optical zoom operation and the electronic zoom operation.

In addition, although the above embodiment described the image pickup apparatus integrally provided with the image taking optical system, alternative embodiments of the present invention include an image pickup apparatus in which the image taking optical system is interchangeable.

This application claims the benefit of Japanese Patent Application No. 2010-134079, filed on Jun. 11, 2010, which is hereby incorporated by reference herein in its entirety.