Abstract:
The present invention provides an automatic focusing system comprising: a region configuring device which configures a main subject region including a main subject within a photographing screen; a focusing control device which controls focusing so that a focus state of the main subject included in the configured main subject region is a best focus state; a focus state obtaining device which divides the photographing screen into a plurality of regions and obtains a focus state from each region; a focus state storage device which stores the focus state obtained from each region; a movement detecting device which references the stored focus state of each region to detect the movement of a group of regions that are located either within the main subject region and its vicinity or within the main subject region and are in a best focus state; and a region moving device which moves the main subject region in accordance with the movement of the group of regions that are located either within the main subject region and its vicinity or within the main subject region and are in the best focus state.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to an automatic focusing apparatus, and more particularly, to a technique used for detecting correct focus in automatic focusing control of photographic lens.  
         [0003]     2. Description of the Related Art  
         [0004]     Conventionally, in camera systems where an AF area for performing automatic focusing is configured within a photographing screen, either framing is performed so that a subject to be brought into focus enters the AF area, or a position of the AF area within the photographing screen is moved in accordance with the movement of the subject. However, in order to shoot a subject that is either fast-moving or has a drastically changing shape, taking shots while keeping the subject inside the AF area may prove difficult. In order to solve this problem, for example, technologies for tracking a subject within a photographing screen are disclosed in Japanese Patent No. 2663451 and Japanese Patent No. 2675807.  
       SUMMARY OF THE INVENTION  
       [0005]     The technologies disclosed in the above-mentioned Japanese Patent No. 2663451 and Japanese Patent No. 2675807 involved moving a correct focus detection region according to a region configured within a photographing screen where either, a difference in average luminance levels between the inside and the outside of a region or a contrast thereof is maximum. However, with images having a small average luminance difference between a subject and a background, it was difficult to detect the position of the subject based on differences in average luminance levels to track the movement of the subject. In addition, since a region with a high contrast within a photographic screen was not necessarily the region in correct focus, there was the possibility of occurrences of malfunctions such as where the correct focus detection region moves to a subject with high contrast (such as an object, a wall or a billboard and the like with striped patterns) that is not the main subject to be tracked.  
         [0006]     The present invention was made in consideration of these circumstances, and its object is to provide an automatic focusing apparatus capable of maintaining correct focus on a main subject even when the main subject moves within a photographing screen.  
         [0007]     In order to achieve the above object, an automatic focusing apparatus according to a first aspect of the present invention comprises: a region configuring device which configures a main subject region including a main subject within a photographing screen; a focusing control device which controls focusing so that a focus state of the main subject included in the configured main subject region is a best focus state; a focus state obtaining device which divides the photographing screen into a plurality of regions and obtains a focus state from each region; a focus state storage device which stores the focus state obtained from each region; a movement detecting-device which references the stored focus state of each region to detect movement of a group of regions that are located either within the main subject region and its vicinity or within the main subject region and are in a best focus state; and a region moving device which moves the main subject region in accordance with the movement of the group of regions that are located either within the main subject region and its vicinity or within the main subject region and are in the best focus state.  
         [0008]     In the automatic focusing apparatus according to the first aspect, storing a focus state (best focus, front focus, rear focus, blurring or the like) of each region enables accurate detection of a main subject and movement of a main subject region even when a subject with a higher contrast than the main subject exists.  
         [0009]     In an automatic focusing apparatus according to a second aspect of the present invention, the focus state according to the first aspect comprises the respective states of best focus, front focus, rear focus or blurring. The second aspect limits the focus states of the first aspect.  
         [0010]     An automatic focusing apparatus according to a third aspect of the present invention is the automatic focusing apparatus according to the first aspect or the second aspect, further comprising: a subject light separating device which separates a subject light for focus state detection from a main optical path which guides a subject light incident to a photographic lens to a visual image pickup device for obtaining an image signal for either recording or playback; an image pickup device which captures the separated subject light for focus state detection using a plurality of image capturing surfaces placed at positions with optical path lengths that differ from one another; and a focus evaluation value calculation device which calculates, for each region, focus evaluation values of the subject image based on image signals captured and obtained by the plurality of image capturing surfaces of the image pickup device; wherein the focus state obtaining device obtains the focus state of each region based on the focus evaluation values.  
         [0011]     In the automatic focusing apparatus according to the third aspect, since the focus state of each region can be detected from the image signals of one field (or one frame), a main subject region can be moved at high speed and with high precision.  
         [0012]     An automatic focusing apparatus according to a fourth aspect of the present invention is the automatic focusing apparatus according to the first to third aspects, further comprising a movement stopping device which stops the movement of the main subject region by the region moving device, wherein the region configuring device accepts configuration of the main subject region when the movement of the main subject region is stopped.  
         [0013]     In the automatic focusing apparatus according to the fourth aspect, a main subject region can be manually configured, for example, when changing main subjects is desired during shooting.  
         [0014]     An automatic focusing apparatus according to a fifth aspect of the present invention is the automatic focusing apparatus according to the first to third aspects, wherein operation of the region configuration device is preferentially accepted when the region configuration device is executed during the movement of the main subject region by the region moving device.  
         [0015]     In the automatic focusing apparatus according to the fifth aspect, an interruption operation for configuring a main subject region can be performed manually while automatic tracking of the main subject region by the region moving device is in progress.  
         [0016]     According to the present invention, even when a subject with a contrast that is higher than a main subject exists, the main subject can be accurately detected by storing the focus state (best focus, front focus, rear focus, blurring or the like) of each divided region of the photographing screen and moving the main subject region to a best focus position. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]      FIG. 1  is a block diagram showing a main configuration of a television camera system to which an automatic focusing system according to an embodiment of the present invention is applied;  
         [0018]      FIGS. 2A and 2B  are diagrams showing a drive apparatus for an automatic focusing system according to an embodiment of the present invention;  
         [0019]      FIG. 3  is a block diagram showing a main configuration of a photographing lens  11 ;  
         [0020]      FIG. 4  is a graph illustrating focus evaluation values;  
         [0021]      FIG. 5  is a plan view showing an AF operating section  12 ;  
         [0022]      FIG. 6  is a diagram showing a photographing screen;  
         [0023]      FIG. 7  is a graph illustrating a focus state of a subject within the photographing screen of  FIG. 6 ; and  
         [0024]      FIG. 8  is a flowchart showing a flow of processing by a CPU  72  during automatic tracking mode. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0025]     A preferred embodiment of an automatic focusing apparatus according to the present invention will now be described with reference to the accompanying drawings.  
         [0026]      FIG. 1  is a block diagram showing a main configuration of a television camera system to which an automatic focusing system according to an embodiment of the present invention is applied. The television camera system  1  shown in  FIG. 1  comprises a camera main body  10 , a photographing lens  11  and an AF frame operating section  12 . The AF frame operating section  12  will be described later.  
         [0027]     The camera main body  10  includes a visual image pickup device or the like for photographing images to be broadcasted, and outputting or recording image signals of a predetermined format onto a storage medium. The photographing lens  11  is detachably mounted onto a mount section of the camera main body  10 .  
         [0028]     An optical system of the photographing lens  11  comprises a focusing lens group  14 , a zoom lens group  16 , an iris (diaphragm)  18 , a relay lens group  20 , and an extender  21  or the like.  
         [0029]     The extender  21  is provided between the iris  18  and the relay lens group  20 , and comprises a plurality of lens units  21   a  capable of advancing and retreating in regards to an optical axis O. Each lens unit  21   a  consists of, for instance, a plurality of lenses at magnifications of 2×, 1×, 0.8× and the like.  
         [0030]     The relay lens group  20  is composed of affront-side relay lens  20 A and a rear-side relay lens  20 B. A half mirror  22  for separating a subject light for focus state detection from a subject light incident via the photographic lens  11  is placed on the optical axis O between the front-side relay lens  20 A and the rear-side relay lens  20 B. The half mirror  22  is positioned so that its mirror surface  22   a  is roughly at 45 degrees to the optical axis O of the photographing lens  11 , and reflects subject light passing through the front-side relay lens  20 A at roughly a right angle, thereby dispersing as an optical axis O′ from the visual image subject light.  
         [0031]     The subject light transmitted through the half mirror  22  is projected as the visual image subject light from the rear end-side of the photographing lens  11 , and enters an image capturing section  24  of the camera main body  10 . While a detailed description of the image capturing section  24  will be omitted, subject light incident to the image capturing section  24  is separated into, for instance, light of the three colors of red, green and blue by a color separation optical system, and are then incident to image capturing surfaces of the visual image pickup device respectively provided for each color. Color visual images for broadcasting or the like are thereby photographed. The reference character P in the drawing designates a focus surface P, which is a position on the optical axis O that is optically equivalent to the photographing surface of the visual image pickup device.  
         [0032]     The subject light reflected by the half mirror  22  proceeds as a focus state detection subject light along an optical axis O′ roughly perpendicular to the optical axis O, and is incident to a focus state detecting section  30  via a formed image position changing lens  26 .  
         [0033]     The focus state detecting section  30  comprises a beam splitter  32  which bisects the focus state detection subject light, two focus state detection image pickup devices A and B to which the focus state detection subject light bisected by the beam splitter  32  enters, and drive apparatuses  34  which drive the focus state detection image pickup devices A and B.  
         [0034]     The beam splitter  32  is composed of two prisms  32   a  and  32   b . As described above, the focus state detection subject light separated from the subject light by the half mirror  22  proceeds along the optical axis O′, and first enters the prism  32   a . At the prism  32   a , the focus state detection subject light is divided into a reflected light and a transmitted light by a half mirror  32   c , and the reflected light proceeds along an optical axis O″ to enter the focus state detection image pickup device A, while the transmitted light is incident to the prism  32   b  before entering the focus state detection image pickup device B.  
         [0035]     For instance, CCDs (Charge Coupled Devices) for photographing black and white or color images are used as the focus state detection image pickup devices A and B.  
         [0036]     The drive apparatuses  34  respectively drive the focus state detection image pickup devices A and B along the optical axes O″ and O′. The drive apparatuses  34  respectively provided for the focus state detection image pickup devices A and B have similar structures. Therefore, the drive apparatus  34  for the focus state detection image pickup device A will now be described in detail.  
         [0037]      FIGS. 2A and 2B  are diagrams showing a:drive apparatus for an automatic focusing system according to an embodiment of the present invention.  FIG. 2A  is a side view, while  FIG. 2B  is a plan view. As shown in  FIGS. 2A and 2B , the drive apparatus  34  comprises a holding frame  40  provided on a photographing lens  11  side, a frame  42  for supporting the focus state detection image pickup device A (B), a spring  44 , a motor  46 , a potentiometer  48 , and a rotating shaft  50  with a male screw provided on its circumferential surface.  
         [0038]     Guide grooves  40   a  and  40   b , roughly parallel to the optical axis O′ (O″), are formed on the holding frame  40 . These guide grooves  40   a  and  40   b  support the frame  42  to move slidably in a direction parallel to the optical axis O′ (O″). By sliding the frame  42  along the guide grooves  40   a  and  40   b , the focus state detection image pickup device A supported by the frame  42  can be moved back and forth along the optical axis O′ (O″) (arrow in  FIG. 2A ).  
         [0039]     A screw  44  that applies biasing force to the frame  42  is provided on an edge of the guiding groove  40   b  of the holding frame  40 . Due to the screw  44 , the frame  42  is constantly biased in a direction corresponding to the right side in  FIG. 2A .  
         [0040]     On the other hand, a support hole  52  which supports the rotating shaft  50  to be rotationally movable is formed on an edge of the guide groove  40   b  that faces the screw  44  of the holding frame  40 . A female screw which screws on to the male screw of the rotating shaft  50  is formed on the inner circumferential surface of the support hole  52 . A front end section (left in  FIG. 2A ) of the rotating shaft  50  is in contact with the frame  42 , and biases the frame  42  against the biasing force of the screw  44  towards the left in  FIG. 2A  by the feeding effect of the screw caused by the rotational movement of the rotating shaft  50  and the translatory effect of the rotating shaft  50 .  
         [0041]     A gear  54  is mounted to a rear end section of the rotating shaft  50 . A gear  58  mounted to a rotation detecting input shaft  56  of the potentiometer  48  meshes with the gear  54 . In addition, the gear  58  meshes with a gear  62  mounted on an output shaft  60  of the motor  46 .  
         [0042]     In the drive apparatus  34  thus configured, the focus state detection image pickup device A (B) can be driven back and forth along the optical axis O′ (O″), supported by the frame. 42 , by driving the motor  46 . In addition, rotation of the gear  58  is detected by the potentiometer  48 . The rotation detection by the potentiometer  48  enables detection of the position of the focus state detection image pickup device A (B), to be described in detail later.  
         [0043]      FIG. 3  is a block diagram showing a main configuration of a photographing lens  11 . Images photographed by the focus state detection image pickup devices A and B are inputted to a signal processing section  70 . The signal processing section  70  detects focus states of the photographing lens  11  based on the inputted image signals, and comprises a central processing unit (CPU)  72  which functions as a control device, as well as an A/D converter  74 , a D/A converter  76 , a focusing demand  78 , a zoom demand  80  and the like.  
         [0044]     The CPU  72  functions both as a control device which controls according to a predetermined program devices such as the focusing lens group  14  or the zoom lens group  16  within the photographing lens  11 , and as a control device for controlling the focus state detection image pickup devices A and B. The CPU  72  comprises a ROM storing a control program and various data tables necessary for control or calculations, a RAM to be used as a working storage area, and the like.  
         [0045]     Focus of the photographing lens  11  is controlled by manual focusing (MF) or automatic focusing (AF).  
         [0046]     During MF, a focusing demand  78  outputs focusing demand data which instructs a moving position of the focusing lens group  14  via the A/D converter  74  to the CPU  72  in response to an amount of rotational operation of a focus knob, not shown, provided on a periphery of the photographing lens  11 . Based on the focusing demand data, the CPU  72  outputs a control signal to a drive circuit  84  of a focusing motor  82 , and drives the focusing lens group  14  of the photographing lens  11 . At the CPU  72 , movement speed of the focusing lens group  14  and the like is calculated based on the loaded focusing demand data and positional data of the focusing lens group  14  inputted via the A/D converter  74  from a focusing potentiometer  86 .  
         [0047]     On the other hand, a zoom demand  80  outputs zoom demand data which instructs moving speed of the zoom lens group  16  via the AID converter  74  to the CPU  72  in response to a direction and an amount of rotation of a zoom ring which is provided to be rotationally movable on a periphery of the photographing lens  11 . Based on the zoom demand data, the CPU  72  outputs a control signal to a drive circuit  90  of a zoom motor  88 , and drives the zoom lens group  16  of the photographing lens  11 . At the CPU  72 , movement of the zoom lens group  16  and the like is calculated based on the loaded zoom demand data and positional data of the zoom lens group  16  inputted via the A/D converter  74  from a potentiometer  92 .  
         [0048]     The CPU  72  also calculates a drive amount of an iris motor  96  based on an diaphragm value data inputted from a potentiometer  94  for the iris  18  via the A/D converter  74 , and an iris control signal provided by the camera main body  10 , and outputs a control signal for the iris motor  96  to a drive circuit  98  of the iris motor  96  via the D/A converter  76 .  
         [0049]     The CPU  72  further outputs a lens unit change signal for the extender  21  to a drive circuit  102  of the extender  21  via the D/A converter  76 , depending on operation of an extender select lever, not shown, provided on the exterior of the photographing lens  11 . Receiving this signal, the drive circuit  102  drives a drive motor  104  of the extender  21 , and advances a selected lens unit onto the optical axis O (refer to  FIG. 1 ). The reference numeral  106  designates a sensor for detecting the type of the lens unit advanced onto the optical axis O.  
         [0050]     During AF, images photographed by the focus state detection image pickup devices A and B are outputted to the CPU  72  of the signal processing section  70 . The CPU  72  detects the focus state of the photographing lens  11  based on visual image signals obtained from the focus state detection image pickup devices A and B. The CPU  72  next outputs a control signal to the drive circuit  84  of the focusing motor  82  based on the detected focus state via the D/A converter  76 , and performs AF control of the photographing lens  11 . This AF control will be described later.  
         [0051]     A motor  46  of the drive apparatus  34  of the focus state detection image pickup device A is activated based on a drive signal from a drive circuit  110 . The drive circuit  110  drives the motor  46  based on a control signal outputted from the D/A converter  76  of the signal processing section  70 . Thus, the movement of the focus state detection image pickup device A is controlled.  
         [0052]     The potentiometer  48  detects the position of the focus state detection image pickup device A based on the number of rotations of the input shaft  56  (refer to  FIG. 2 ), and outputs the positional data thereof to the A/D converter  74  of the signal processing section  70 .  
         [0053]     The drive apparatus  34  of the focus state detection image pickup device B is similar in configuration to that of the focus state detection image pickup device A, and the motor  46  is driven based on a control signal outputted from the D/A converter  76  to control movement of the focus state detection image pickup device B. In addition, the position of the focus state detection image pickup device B is detected by the potentiometer  48 , and positional data thereof is outputted to the A/D converter  74  of the signal processing section  70 .  
         [0054]     Processing for focus state detection will now be described specifically. Images of a subject captured by the focus state detection image pickup devices A and B are respectively outputted to the signal processing section  70  as video signals with a predetermined format, and are inputted to the CPU  72  after being converted to focus evaluation value (VA, VB) signals that indicate sharpness or contrast of the images by bypass filters  120   a  and  120   b , A/D converters  122   a  and  122   b , gate circuits  124   a  and  124   b , and adding machines  126   a  and  126   b  of the signal processing section  70 . For instance, when CCDs which photograph black and white images are used as the focus state detection image pickup devices A and B, video signals outputted from the focus state detection image pickup devices A and B to the signal processing section  70  become luminance signals indicating luminance of each pixel composing each screen.  
         [0055]     Processing for obtaining the focus evaluation values VA and VB will now be explained. The video signals outputted from the focus state detection image pickup devices A and B are respectively inputted to the bypass filters  120   a  and  120   b , and their high frequency components are extracted. The signals of the high frequency components extracted by the bypass filters  120   a  and  120   b  are respectively converted into digital signals by the A/D converters  122   a  and  122   b . Next, among the one screen&#39;s worth (one field&#39;s worth) of the digital signals of the images photographed by the focus state detection image pickup devices A and B, only the digital signals corresponding to pixels within a predetermined focus area (for instance, the center portion of the screen) are respectively extracted by the gate circuits  124   a  and  124   b . The values of digital, signals of the extracted range are added by the adding machines  126   a  and  126   b . A total sum of the values of the high frequency components of the video signals within the predetermined focus area is thereby obtained, and the obtained values become the focus evaluation values VA and VB, which indicate a level of sharpness of the image within the predetermined focus area.  
         [0056]     Various synchronization signals are applied from a synchronization&#39;signal generating circuit, not shown, to the focus state detection image pickup devices A and B and the respective circuits such as the gate circuits  124   a  and  124   b  to achieve synchronization of processing performed at each circuit. In addition, a vertical synchronization signal (V signal) for each field of the video signal is applied from the synchronization signal generating circuit to the CPU  72 .  
         [0057]     Based on the focus evaluation values VA and VB obtained in this manner, the CPU  72  detects a current focus state of the photographing lens  11  in relation to the photographing surface (the focus surface P shown in  FIG. 1 ) of the visual image pickup device.  
         [0058]     Effects of the automatic focusing apparatus according to the present invention will now be described. First, a description will be provided on focus evaluation values.  FIG. 4  is a graph illustrating focus evaluation values. In  FIG. 4 , a horizontal axis represents focus positions of the photographing lens  12 , while a vertical axis represents focus evaluation values. Curved lines SA and SB indicated by continuous lines represent focus evaluation values respectively obtained from the automatic focusing image pickup devices A and B, while a curved line SC indicated by a dotted line is a focus evaluation value obtained from an visual image pickup device (P). On the curved line SC, a position F 1  where the focus evaluation value reaches maximum (maximal) is the correct focus position of the visual image pickup device C.  
         [0059]     When the focus position of the photographing lens  11  is set to the correct focus position F 1 , the focus evaluation values obtained from each focus state detection image pickup devices A and B are values VA 1  and VB 1  corresponding to the position F 1  on the respective curved lines SA and SB. In this case, as for the relationships between each focus evaluation value, the focus evaluation value VA 1  obtained from the focus state detection image pickup device A and the focus evaluation value VB 1  obtained from the focus state detection image pickup device B are equal to each other, while a focus evaluation value VC 1  of the focus state detection image pickup device C assumes a different value (VA 1 =VB 1 , VA 1 ≠VC 1 , VB 1 ≠VC 1 ). Therefore, it can be-understood, that when-the focus evaluation value VA 1  obtained from the focus state detection image pickup device A and the focus evaluation value VB 1  obtained from the focus state detection image pickup device B are equal to each other, while a focus evaluation value VC 1  of a focus state detection image pickup device C assumes:a different value, the focus position of the photographing lens  11  is set at the correct-focus position F 1 .  
         [0060]     On the other hand, when the focus position of the photographing lens  11  is set to a position F 2  on the near side of the correct focus position F 1 , the focus evaluation values obtained from each focus state detection image pickup devices A and B are values VA 2  and VB 2  corresponding to the position F 2  on the respective curved lines SA and SB. In this case, as for the relationship between the focus evaluation value VA 2  obtained from the focus state detection image pickup device A and the focus evaluation value VB 2  obtained from the focus state detection image pickup device B, the focus evaluation value VA 2  obtained from the focus state detection image pickup device A is greater than the focus evaluation value VB 2  obtained from the focus state detection image pickup device B (VA 2 &gt;VB 2 ). Therefore, it can be understood that when the focus evaluation value VA 2  obtained from the focus state detection image pickup device A is greater than the focus evaluation value VB 2  obtained from the focus state detection image pickup device B, the focus position of the photographing lens  11  is set to the near side of the correct focus position F 1 , i.e., at a front-focus position.  
         [0061]     Similarly, when the focus position of the photographing lens  11  is set to a position F 3  on the infinity side of the correct focus position F 1 , the focus evaluation values obtained from each focus state detection image pickup devices A and B are values VA 3  and VB 3  corresponding to the position F 3  on the respective curved lines SA and SB. In this case, as for the relationship between the focus evaluation value VA 3  obtained from the focus state detection image pickup device A and the focus evaluation value VB 3  obtained from the focus state detection image pickup device B, the focus evaluation value VA 3  obtained from the focus state detection image pickup device A is smaller than the focus evaluation value VB 3  obtained from the focus state detection image pickup device B (VA 3 &lt;VB 3 ). Therefore, it can be understood that when the focus evaluation value VA 3  obtained from the focus state detection image pickup device A is smaller than the focus evaluation value VB 3  obtained from the focus state detection image pickup device B, the focus position of the photographing lens  11  is set to the infinity side of the correct focus position F 1 , i.e., at a rear focus position.  
         [0062]     As the zoom lens group  16  of the photographing lens  11  is operated to shift the focal length to a wide angle side (i.e., shortened), the amount of displacement of the focus position corresponding to the optical path length increases, and the curved lines SA and SB become more spaced in relation to the focus position. When a difference in focus evaluation values is not detected, the positions of the focus state detection image pickup devices A and B can be moved so that the optical path length difference decreases, making the curved lines SA and SB approach each other, and thereby enabling detection of a focus state.  
         [0063]     As seen, the automatic focusing apparatus according to the present embodiment enables optimum configuration of optical path lengths by moving focus state detection image pickup devices back and forth along the direction of an optical axis of a focus state detection subject light, thereby constantly enabling detection of appropriate focus states.  
         [0064]     The AF frame operating section  12  will now be described.  FIG. 5  is a plan view showing the AF operating section  12 . As shown in  FIG. 5 , the AF operating section  12  comprises a joystick  130 , an AF start switch  132  and a tracking starting switch  134 . The joystick  130  is a member that is operated to designate AF area positions within the photographing screen. The AF start switch  132  is a member that is operated to perform automatic focusing so that a subject within the AF area designated by the joystick  130  achieves best focus. The tracking starting switch  134  is a switch for initiating an automatic tracking mode that automatically tracks the AF area in accordance with the movement of the subject in best focus in the photographing screen.  
         [0065]      FIG. 6  is a diagram showing a photographing screen. As shown in  FIG. 6 , the photographing screen  140  is divided into a plurality of regions  140 A. Reference numeral  142  designates an AF frame, which indicates an AF area within the photographing screen. The automatic focusing apparatus according to the present embodiment respectively detects a focus state for each region  140 A. In  FIG. 6 , a “0” sign is displayed for a region  140 A that includes a subject in best focus, a “+” sign is displayed for a region  140 A that includes a subject in front focus, and a region  140 A that includes a subject in rear focus is displayed by a “−” sign. A region  140 A displayed by none of the signs “0”, “+” or “−” is either a region with a blurred subject or a region without a subject.  
         [0066]     In the present embodiment, as shown in  FIG. 6 , an input is first provided by operating the joystick  130  to move the AF frame  142  to the position of a main subject  144  (person). When the AF start switch  132  is pressed, automatic focusing is performed so that the main subject  144  in the AF frame  142  comes into best focus. At this point, as shown in  FIGS. 6 and 7 , a group of regions including the subject  144  (person) near the AF frame  142  is now in best focus, and a group of regions including a subject  146  (tree), shown to the right of the subject  144  in  FIG. 6 , is now in rear focus, while a subject  148  (a subject with high contrast, such as an multi-colored object with a significant difference in luminance), shown to the left of the subject  144  in  FIG. 6 , is now in front focus. Each focus state of the regions  140 A is detected by the CPU  72  and stored in a RAM.  
         [0067]     Next, when the tracking starting switch  134  is pressed and the mode is set to automatic tracking mode, the focus state of each region  140 A stored in the RAM by the CPU  72  is referenced, and a movement of a group of regions in best focus (in  FIG. 6 , the group of regions displayed by “0” signs in the AF frame  142  and its vicinity) is detected. Then, the AF frame  142  moves in accordance with the movement of a group of regions in best focus, while automatic focusing is simultaneously performed so that the subject  144  in the AF frame  142  comes into best focus.  
         [0068]     In the present embodiment, for instance, when the tracking starting switch  134  is pressed during automatic tracking mode, the automatic tracking mode is deactivated, thereby stopping the movement of the AF frame  142  that has been moving in accordance with the movement of the main subject  144 . In this case, the position of the AF frame  142  can be manually designated using the joystick  130 .  
         [0069]     In addition, when the joystick  130  is operated during automatic tracking mode, automatic tracking can be arranged to terminate to preferentially accept manual operation by the joystick  130 .  
         [0070]      FIG. 7  is a graph illustrating a focus state of a subject within the photographing screen of  FIG. 6 . A horizontal axis of  FIG. 7  represents focus positions of the focusing lens group  14 , while a vertical axis represents focus evaluation values. In  FIG. 7 , the focus evaluation values of the three subjects  144  to  148  respectively detected for each region  140 A are shown on the same graph. As shown in  FIG. 7 , although the focus evaluation value of the main subject  144  is lower than those of the subjects  146  and  148 , by respectively detecting a focus state (best focus, front focus, rear focus, blurring or the like) for each region  140 A, the AF frame  142  can be tracked so that the main subject  144  comes into best focus.  
         [0071]     Next, a flow of processing during automatic tracking mode will be described with reference to  FIG. 8 .  FIG. 8  is a flowchart showing a flow of processing by a CPU  72  during automatic tracking mode. First, an input is provided by operating the joystick  130  to configure the AF frame  142  to overlap with the main subject  144  (step S 10 ). The step S 10  can be arranged so that the size and shape of the AF frame  142  is adjustable according to the size and shape of the main subject  144 . Then, when the AF start switch  132  is pressed, automatic focusing is performed so that the main subject  144  in the AF frame  142  comes into best focus (step S 12 ).  
         [0072]     Next, if not set to automatic tracking mode (No in step S 14 ), the process returns to step S 10  to continue manual configuration of the AF frame. On the other hand, if the tracking starting switch has been pushed and the automatic tracking mode is set (Yes in step S 14 ), a focus state is respectively detected for each region  140 A in the photographing screen  140  and stored in the RAM (step S 16 ). Then, the focus state of each region  140 A stored in the RAM are referenced, and a movement of a group of regions in best focus (in  FIG. 6 , the group of regions displayed by “0” signs) is detected. Then, the AF frame  142  moves in accordance with the movement of a group of regions in best focus (step S 18 ), while automatic focusing is simultaneously performed so that the subject  144  in the AF frame  142  comes into best focus (step S 20 ). In step S 18 , the AF frame  142  can be arranged, for instance, to move so as to entirely include the group of regions in best focus, or to move so that the center (or the center of gravity) of the AF frame  142  is congruent with the center of gravity of the group of regions in best focus. In addition, when the size of the group of regions in best focus changes, the size of the AF frame  142  can be arranged to change accordingly.  
         [0073]     Then, if photographing under the automatic tracking mode is ongoing (No in step S 22 ), the process returns to step S 16 . On the other hand, if the tracking starting switch  134  is pressed and either the automatic tracking mode is deactivated or photographing is concluded (Yes in step S 22 ), the above processing is terminated.  
         [0074]     According to the present embodiment, by respectively detecting a focus state (best focus, front focus, rear focus, blurring or the like) for each region  140 A in the photographing screen  140 , the main subject  144  can be accurately detected and the AF frame  142  can be tracked even when a subject with a higher contrast than the subject  144  exists.  
         [0075]     In the above-described step S 18 , when the group of regions in best focus in the photographing screen  140  separates into a plurality of groups, for instance, it is conceivable that a plurality of subjects (persons) in the AF frame  142  has started to move independently from each other. In such cases, the AF frame  142  is preferably moved in accordance with a group of regions with the biggest or smallest size, or with a group of regions with a high contrast. In addition, the step S 18  may be arranged so that an indication prompting manual configuration of the AF frame  142  using the joystick  130  is displayed.  
         [0076]     In addition, when zooming is performed during the automatic tracking mode, the present embodiment may be arranged so that the size of the AF frame  142  is adjusted in accordance with such zooming.  
         [0077]     Furthermore, while the present embodiment has been configured so that, a focus state is respectively detected for each region  140 A in the photographing screen  140  by providing a plurality of focus state detection image pickup devices A and B with different optical path lengths, the present invention is not limited to this configuration. For instance, wobbling of the focusing lens group  14  may be performed to detect focus evaluation values, thereby detecting a focus state for each region  140 A.  
         [0078]     Additionally, the configuration of the automatic focusing apparatus according to the present embodiment is not limited to the above. While the present embodiment is configured so that the focus state detection image pickup devices A and B are driven by motors  46 , a configuration in which the focus state detection image pickup devices A and B are driven by an actuator using piezoelectric elements or the like is also possible.  
         [0079]     Moreover, while the present embodiment has been described with respect to an example where the automatic focusing apparatus of the present invention is applied to the photographing lens of a television camera system for purposes of broadcasting or the like, the scope of application of the present invention is not limited to these purposes. For instance, the present invention can also be applied to the photographing lenses of conventional cameras such as digital cameras.