Abstract:
A photography device that includes an imaging component, a focusing component, a magnification alteration component, a display component, an acquisition component and a control component is provided. The focusing component focuses a subject image on an imaging surface of the imaging component. The magnification alteration component alters a magnification of the subject image focused by the focusing component. The acquisition component acquires a focusing evaluation value representing a degree of focusing of the subject image by the focusing component. The control component performs focusing control by controlling the focusing component such that the focusing evaluation value acquired by the acquisition component is at a maximum, and controls the magnification alteration component so as to lower a display magnification of the subject image by the display component if the focusing evaluation value is at or below a pre-specified threshold value.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority under 35 USC 119 from Japanese Patent Application No. 2008-068362, the disclosure of which is incorporated by reference herein. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a photography device and photography method that acquire image information representing a subject image by photography. 
     2. Description of the Related Art 
     Heretofore, it has been proposed that cameras be provided with magnifying zoom functions, which magnify subject images that are photographed. In recent years, installation of high magnification zoom functions even in compact cameras has been desired. 
     When photography is performed using a high magnification zoom function, there is a large difference between the viewing angle to be photographed and a person&#39;s own field of view. Consequently, determining a viewing angle, a photograph composition and the like may be difficult. Thus, in an image obtained with high magnification zoom, if the user&#39;s composition technique or movement is even slightly misplaced, the viewing angle and composition are greatly misplaced. 
     Previously, as a technology for facilitating the determination of an image composition, for example, Japanese Patent Application Laid-Open (JP-A) No. 2001-211360 has described that, with the viewfinder of a video camera that is photographing a moving image, a viewing angle wider than the viewing angle that is being photographed is imaged, and display of a viewing angle range that includes the viewing angle range to be photographed and that is wider than this viewing angle is enabled, in order to enable verification of conditions at the outside of the viewing angle being photographed. 
     Similarly, JP-A No. 7-336569 has described that, when a moving image is being photographed, an optical zoom range of a zoom lens is divided into two or more steps, the optical zoom and an electronic zoom are alternately operated, and when a viewing angle switching switch is operated, only a viewfinder screen returns to a wide-angle display. 
     Furthermore, JP-A No. 5-130481 has described limiting a zoom magnification in accordance with an image shake ratio, in order to prevent image shake that exceeds an image shake correction range from occurring during photography. 
     However, the technologies of JP-A Nos. 2001-211360, 7-336569 and 5-130481 have a problem, are not being able to respond to a case of a large displacement from a subject image that is to be photographed. 
     That is, in a case of a large displacement from the subject image that is to be photographed, it is necessary for a photographer to carry out operations of temporarily lowering the zoom ratio until the subject image that is to be photographed re-enters a range in which photography is possible, identifying the subject image that is to be photographed, and then increasing the zoom ratio again. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in order to solve the problem described above, and an object of the present invention is to provide a photography device and photography method capable of assisting in a determination of composition by a photographer when altering a magnification ratio of a subject image and performing photography. 
     In order to achieve the objective described above, a first aspect of the present invention is a photography device including: an imaging component that images a subject and acquires an image representing the subject; a focusing component that focuses a subject image on an imaging surface of the imaging component; a magnification alteration component that alters a magnification of the subject image focused by the focusing component; a display component that displays the subject image in real time on the basis of image information acquired by the imaging component; an acquisition component that acquires a focusing evaluation value representing a degree of focusing of the subject image from the imaging component; and a control component that performs focusing control by controlling the imaging component such that the focusing evaluation value acquired by the acquisition component is at a maximum, and controls the magnification alteration component so as to lower a display magnification of the subject image by the display component if the focusing evaluation value is at or below a pre-specified threshold value. 
     According to the first aspect, the focusing control is carried out on the basis of the focusing evaluation value. If the focusing evaluation value is below the pre-specified threshold, the display magnification of the subject image is lowered. Thus, if the subject image has been excessively magnified, or if the target of photography has been misplaced, or the like, the subject is displayed at the display component in a wider range than the photography range therebefore, and the photographer can more easily ascertain a composition that is to be photographed. Therefore, according to the first aspect, a determination of composition by a photographer when altering a magnification ratio of a subject image and performing photography can be assisted. 
     A second aspect of the present invention is the photography device according to the first aspect, further including a storage component that stores the focusing evaluation value acquired by the acquisition component, wherein the control component controls so as to lower the display magnification of the subject image by the display component if the focusing evaluation value acquired by the acquisition component at a current point in time has fallen by at least a pre-specified threshold value from the focusing evaluation value stored by the storage component a predetermined duration before. 
     A third aspect of the present invention is the photography device according to the second aspect, wherein the control component increases a degree of the lowering of the display magnification by the display component in accordance with a magnitude of a degree of the fall of the focusing evaluation value. 
     A fourth aspect of the present invention is the photography device according to the first aspect, wherein the control component, before controlling so as to lower the display magnification of the subject image by the display component, controls the display component so as to implement a pre-specified display relating to this control. 
     A fifth aspect of the present invention is a photography device including: an imaging component that images a subject and acquires an image representing the subject; a focusing component that focuses a subject image on an imaging surface of the imaging component; a magnification alteration component that alters a magnification of the subject image focused by the focusing component; a display component that displays the subject image in real time on the basis of image information acquired by the imaging component; an acquisition component that divides the subject image represented by the image information into a pre-specified number of divisions, and acquires a focusing evaluation value representing a degree of focusing of the subject image from the imaging component on the basis of the image information that corresponds to at least one region of regions of the divisions; and a control component that performs focusing control by controlling the imaging component such that the focusing evaluation value acquired by the acquisition component is at a maximum, stores a division region that is used when performing the focusing control as a focusing subject, and, if the focusing evaluation value of the focusing subject falls significantly, controls the display component so as to implement a display indicating the fall. 
     A sixth aspect of the present invention is a photography method including: (a) displaying, in real time at a display component, a subject image based on image information that is focused at an imaging surface of an imaging component, which images a subject and acquires an image representing the subject; (b) acquiring a focusing evaluation value representing a degree of focusing of the subject image; and (c) performing focusing control that focuses the subject image at the imaging surface such that the acquired focusing evaluation value is at a maximum and, if the focusing evaluation value is at or below a pre-specified threshold value, controlling so as to lower a display magnification of the subject image by the display component. 
     As described above, according to the present invention, there is an effect in that a determination of composition by a photographer when altering a magnification ratio of a subject image and performing photography can be assisted. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is external views of a digital camera relating to a first exemplary embodiment of the present invention. 
         FIG. 2  is a block diagram showing structure of an electronic system of the digital camera relating to the first exemplary embodiment of the present invention. 
         FIG. 3A  shows an example of a change in an AF evaluation value when image contrast is maximized when a zoom ratio is altered. 
         FIG. 3B  shows magnitudes of viewing angles when the zoom ratio is altered. 
         FIG. 4A ,  FIG. 4B  and  FIG. 4C  show respective images obtained when the same subject image is photographed with different zoom ratios. 
         FIG. 5  is a flowchart showing a flow of photography processing relating to the first exemplary embodiment of the present invention. 
         FIG. 6A  and  FIG. 6B  are a flowchart showing a flow of photography processing relating to a second exemplary embodiment of the present invention. 
         FIG. 7  is a graph showing an example of zoom ratio alteration amounts corresponding to comparison values, for a variant example of the second exemplary embodiment of the present invention. 
         FIG. 8A ,  FIG. 8B ,  FIG. 8C ,  FIG. 8D  and  FIG. 8E  are explanatory views of examples of changes in display states when the control shown in  FIG. 7  is performed. 
         FIG. 9A  and  FIG. 9B  are a flowchart showing a flow of photography processing relating to a third exemplary embodiment of the present invention. 
         FIG. 10A ,  FIG. 10B ,  FIG. 10C  and  FIG. 10D  are explanatory views showing examples of display states in the photography processing relating to the third exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Herebelow, the best embodiment for carrying out the present invention will be described in detail with reference to the drawings. 
     First Exemplary Embodiment 
     Firstly, external structures of a digital camera  10  relating to the first exemplary embodiment will be described with reference to  FIG. 1 . As is shown in  FIG. 1 , a lens  12 , for focusing a subject image, and a viewfinder (an OVF, or optical viewfinder)  58 , which is used for determining the composition of a subject to be photographed, are provided at the front face of the digital camera  10 . A release button (“shutter”)  56 A, which is pressed for operation by a photographer when photography is to be executed, and a power switch  56 B are provided at an upper face of the digital camera  10 . 
     The release button  56 A relating to the present exemplary embodiment is constituted to be capable of detecting two stages of pressing operation: a state of being pressed down to an intermediate position (herebelow referred to as a half-pressed state) and a state of being pressed down beyond the intermediate position to a final lowermost position (below referred to as a full-pressed state). 
     At the digital camera  10  relating to the present exemplary embodiment, when the release button  56 A is put into the half-pressed state, an AE (automatic exposure) function operates and exposure conditions (a shutter speed and an aperture state) are specified, and then an AF (auto focus) function operates to control focusing. Thereafter, when the release button  56 A is further put into the full-pressed state, exposure (photography) is carried out. 
     An eyepiece portion of the aforementioned viewfinder  58 , a liquid crystal display (below referred to as an LCD)  30 , a mode switch  56 C, a cross-cursor button  56 D and a zoom control  56 E are provided at a rear face of the digital camera  10 . The LCD  30  is for displaying subject images represented by digital image data obtained by photography, and various menu screens, messages and the like. The mode switch  56 C is operated by sliding to set one of a photography mode, which is a mode for carrying out photography, and a replay mode, which is a mode for displaying (replaying) at the LCD  30  subject images represented by digital image data which has been obtained by photography. The cross-cursor button  56 D is structured to include four arrow keys representing four directions of movement-up, down, left and right—in a display region of the LCD  30 . The zoom control  56 E is operated when zooming (magnification or reduction) of the subject image is to be carried out at a time of photography. 
     The cross-cursor button  56 D is structured to include a total of five keys, the four arrow keys representing the four directions of movement up, down, left and right in the display region of the LCD  30 , and a select key disposed at a central portion of the four arrow keys. The zoom control  56 E is structured by a telephoto switch, corresponding to the position of the ‘T’ in  FIG. 1 , which is operated when the subject image is to be magnified, and a wide angle switch, corresponding to the position of the ‘W’ in  FIG. 1 , which is operated when the subject image is to be reduced. 
     Next, structure of an electronic system of the digital camera  10  relating to the present exemplary embodiment will be described with reference to  FIG. 2 . As shown in  FIG. 2 , the digital camera  10  is structured to include a CPU (central processing unit)  32 , a first memory  38  and a second memory  40 . The CPU  32  administers overall operations of the digital camera  10 . The first memory  38  is used as a work memory at times of execution of various processes by the CPU  32 , and the like. The second memory  40  principally stores the digital image data obtained by photography. The CPU  32 , the first memory  38  and the second memory  40  are respectively connected to one another through a bus. 
     The digital camera  10  is further structured to include a media controller  42 , which is for enabling access by the digital camera  10  to a removable recording medium  42 A in the body of the digital camera  10 . The media controller  42  is also connected to the bus. 
     Thus, from the CPU  32 , access to the first memory  38  and the second memory  40 , and access to the recording medium  42 A via the media controller  42 , can be respectively implemented. 
     The first memory  38  may be constituted by, for example, an SDRAM (synchronized dynamic random access memory) and the second memory  40  may be constituted by, for example, a VRAM (video RAM), respectively. 
     As is also shown in  FIG. 2 , an optical unit  13 , a CCD (charge coupled device)  14  and a timing generator  48  are provided in the digital camera  10 . The optical unit  13  is structured to include the aforementioned lens  12 . The CCD  14  is disposed to rearward on the optical axis of the lens  12 . The timing generator  48  principally generates timing signals for driving the CCD  14  and provides the timing signals to the CCD  14 . 
     An input terminal of the timing generator  48  is connected to the CPU  32  and an output terminal of the timing generator  48  is connected to the CCD  14 . Driving of the CCD  14  is controlled by the CPU  32  via the timing generator  48 . 
     The lens  12  included in the optical unit  13  relating to the present exemplary embodiment includes a plurality of lenses, and is constituted to serve as a zoom lens capable of altering the focusing distance (altering magnification). A lens driving mechanism is provided that is structured to include a zoom motor, a focus adjustment motor and an aperture driving motor. Output terminals of motor driving portions  50 A,  50 B and  50 C are connected to a zoom motor  13 A, a focus adjustment motor  13 B and an aperture driving motor  13 C, respectively. 
     The input terminals of the motor driving portions  50 A,  50 B and  50 C are each connected to the CPU  32 . The zoom motor  13 A, focus adjustment motor  13 B and aperture driving motor  13 C are respectively driven by driving signals provided from the respective motor driving portions  50  under the control of the CPU  32 . 
     When an optical zoom magnification is to be altered, the CPU  32  controls to drive the zoom motor  13 A and the focusing distance of the lens  12  included in the optical unit  13  is altered. 
     The digital camera  10  is yet further structured to include a correlated doubled sampling circuit (below referred to as a CDSAMP)  16  and an analog/digital converter (below referred to as an ADC)  18 , which converts inputted analog signals into digital data. An input terminal of the CDSAMP  16  is connected to an output terminal of the CCD  14 , and an output terminal of the CDSAMP  16  is connected to an input terminal of the ADC  18 . 
     At the CDSAMP  16 , with a view to moderating noise and the like included in output signals from the CCD  14 , processing is carried out to obtain accurate image data by taking differences between feed-through component levels and image signal component levels which are included in the output signals of individual pixels, which are solid state imaging elements. 
     Operation portions  56 , including the aforementioned release button  56 A, power switch  56 B, mode switch  56 C, cross-cursor button  56 D and zoom control  56 E, are connected to the CPU  32 . Thus, the CPU  32  can continuously identify operational states of the respective operation portions  56 . 
     The digital camera  10  is structured to include an image input controller  20 , an image signal processing circuit  22 , a compression/expansion processing circuit  24  and a display control circuit  28 . The image input controller  20  incorporates a line buffer with a predetermined capacity and performs control to directly store inputted digital image data in a predetermined region of the second memory  40 . The image signal processing circuit  22  carries out various kinds of image processing on the digital image data. The compression/expansion processing circuit  24  performs compression processing on the digital image data into a predetermined compression format, and performs expansion processing on digital image data that has been compressed. The display control circuit  28  supplies, to the LCD  30 , signals for displaying images represented by digital image data and menu screens and the like at the LCD  30 . Here, an output terminal of the ADC  18  is connected to an input terminal of the image input controller  20 . 
     The digital camera  10  is still further structured to include an AF detection circuit  34 , which detects a physical quantity required for operating the aforementioned AF function, and an AE/AWB detection circuit  36 , which detects physical quantities required for operating the aforementioned AE function and an AWB (automatic white balance) function. 
     As the physical quantity detected by the AF detection circuit  34 , an AF evaluation value which represents a high frequency component of luminance (a contrast value) in an AF region of an image obtained by imaging by the CCD  14  is detected. As the physical quantities detected by the AE/AWB detection circuit  36 , luminance information and color difference information which represent brightness of an image obtained through the CCD  14  are detected. 
     That is, in the present exemplary embodiment, a “TTL” (through the lens) system is used as the above-mentioned AF function. The TTL system sets the position of a focusing lens by controlling driving of the focus adjustment motor  13 B via the motor driving portion  50 A, on the basis of the AF evaluation value detected by the AF detection circuit  34 , so as to maximize contrast in the image obtained by imaging by the CCD  14 . 
     The above-mentioned image input controller  20 , image signal processing circuit  22 , compression/expansion processing circuit  24 , display control circuit  28 , AF detection circuit  34  and AE/AWB detection circuit  36  are respectively connected to one another through the above-mentioned bus that is connected to the CPU  32  and the like. 
     Thus, the CPU  32  can implement control of operations of each of the image input controller  20 , the image signal processing circuit  22 , the compression/expansion processing circuit  24  and the display control circuit  28 , and of acquisition of the physical quantities detected by the AF detection circuit  34  and the AE/AWB detection circuit  36 . 
     Now, in the digital camera  10  relating to the present exemplary embodiment, if the AF evaluation value at which the image contrast is maximized falls below a predetermined threshold value Th, then the zoom ratio is lowered. 
       FIG. 3A  shows an example of a change in AF evaluation value when image contrast is maximized when the zoom ratio is altered. As is shown in  FIG. 3A , the higher the zoom ratio, the more difficult it is to raise the contrast of the image, and the smaller the AF evaluation value tends to be. Note that the trend shown in  FIG. 3A  is an example; changes are not limited to being linear as shown in  FIG. 3A , and will differ in accordance with compositions, shapes and the like of subject images. 
       FIG. 3B  shows magnitudes of viewing angles when the zoom ratio is altered. The viewing angles represent angles of incident light. The larger the viewing angle, the more subjects are included in an imaging region, while the smaller the viewing angle, the fewer subjects are included in the imaging region. 
       FIG. 4A  to  FIG. 4C  show respective images obtained when the same subject image is photographed with different zoom ratios.  FIG. 4A  and  FIG. 4B  show cases in which the subject image is photographed with high zoom ratios, and  FIG. 4C  shows a case in which the subject image is photographed with a low zoom ratio. 
     When the zoom ratio is low, as shown in  FIG. 4C , many subject images are imaged, whereas when the zoom ratio is high, as shown in  FIG. 4A , the imaging region is narrower, the AF evaluation value of a subject image is lower, and there is a tendency for subject images to not be expressed clearly. Furthermore, if the target of photography is misplaced when the zoom ratio is high, due to the effects of hand shake or the like, then there is a tendency for it to be unclear what is being pictured, as is shown in  FIG. 4B . 
     That is, as shown in  FIG. 4A  and  FIG. 4B , when the AF evaluation value is lower than the threshold value Th shown in  FIG. 3A , then, as shown by the broken line arrow in  FIG. 3B , the zoom ratio is lowered and the viewing angle is increased, and a range of visible subject images is widened. 
     Next, operation of the digital camera  10  relating to the present exemplary embodiment will be described. 
     As overall operations of the digital camera  10  at a time of photography, firstly, imaging is carried out by the CCD  14  through the optical unit  13 , and signals representing a subject image are sequentially outputted from the CCD  14 . Hence, the signals outputted from the CCD  14  are sequentially inputted into the CDSAMP  16  and subjected to correlated double sampling processing, and then inputted into the ADC  18 . The ADC  18  converts signals of R (red), G (green) and B (blue) inputted from the CDSAMP  16  into respective 12-bit R, G and B signals (i.e., digital image data), and outputs the same to the image input controller  20 . 
     The image input controller  20  collects the digital image data sequentially inputted thereto from the ADC  18  in the line buffer incorporated therein, and temporarily stores the digital image data in the predetermined region of the second memory  40 . 
     The digital image data stored in the predetermined region of the second memory  40  is read out by the image signal processing circuit  22  under the control of the CPU  32 , and is subjected to white balance adjustment, in which digital gain is applied in accordance with the physical quantities detected by the AE/AWB detection circuit  36 . In addition, gamma processing and sharpness processing are applied and 8-bit digital image data is generated. Further, YC signal processing is applied to generate luminance signals Y and chroma signals Cr and Cb (below referred to as YC signals). The YC signals are stored at a region of the second memory  40  different from the above-mentioned predetermined region. 
     Herein, the LCD  30  is constituted to be employable as a viewfinder (an EVF, which is an electronic viewfinder), displaying a moving image obtained by continuous imaging by the CCD  14  (a through-image). When the LCD  30  is employed as a viewfinder in this manner, the YC signals that are generated are outputted to the LCD  30  via the display control circuit  28 . Hence, the through-image is displayed at the LCD  30 . 
     Now, when the release button  56 A is put into the half-pressed state by a user, as mentioned earlier, the AE function operates and sets exposure conditions, and then the AF function operates and performs focusing control. Thereafter, if the user continues on to the full-pressed state, the YC signals that are stored in the second memory  40  at this time are compressed into the predetermined compression format by the compression/expansion processing circuit  24 , and are then recorded to the recording medium  42 A as an image file. 
       FIG. 5  is a flowchart showing a flow of a photography processing program that is executed by the CPU  32  of the digital camera  10  when a photography mode has been set in accordance with a sliding position of the mode switch  56 C. Herebelow, photography processing relating to the present exemplary embodiment will be described with reference to  FIG. 5 . 
     First, in step  100 , display of the through-image is commenced. Then, in step  102 , it is determined whether or not an operation signal representing operation of the zoom control  56 E has been inputted. If this determination is positive, the processing advances to step  104 . In step  104 , the zoom lens is moved in accordance with an operation direction and operation amount of the zoom control  56 E, after which the processing advances to step  106 . On the other hand, if the determination in step  102  is negative, the processing advances to step  106  without executing the processing of step  104 . 
     In step  106 , it is determined whether or not an operation signal representing the release button  56 A being put into the half-pressed state has been inputted. If this determination is positive, the processing advances to step  108  and the focusing lens position is fixed, after which the processing advances to step  110 . 
     In step  110 , it is determined whether or not the AF evaluation value detected by the AF detection circuit  34  is at or below the pre-specified threshold Th. If this determination is negative, the processing advances to step  118 , and it is determined whether or not the release button  56 A has been put into the full-pressed state. If the determination in step  118  is positive, the processing advances to step  122 , and photography is implemented by image information provided via the CCD  14  being stored in the recording medium  42 A as still image information. Then, the processing advances to step  124 . 
     If the determination of step  118  is negative, the processing advances to step  120 , and it is determined whether or not the half-pressed state of the release button  56 A has been released. If the determination of step  120  is negative, the processing advances to step  116 . If the determination of step  120  is positive, the processing returns to step  102 . 
     Meanwhile, if the determination of step  110  is positive, it is judged that the zoom ratio is excessively high ( FIG. 4A ) or the target to be photographed has been misplaced due to hand shake ( FIG. 4B ), and the processing advances to step  112 . In step  112 , it is determined whether or not the position of the zoom lens is a position at which the viewing angle is maximized (a state in which the subject image is minimally reduced; i.e., the wide-angle end). If this determination is negative, the processing advances to step  114  and the zoom lens is moved toward the low magnification end, after which the processing advances to step  116 . If the determination in step  112  is positive, it is judged that the zoom ratio is not excessively increased and that hand shake is not a factor at this zoom ratio, and the processing advances to step  118 . 
     In step  116 , the AF evaluation value detected by the AF detection circuit  34  in the current state is acquired, after which the processing returns to step  110 . 
     In step  124 , it is determined whether or not photography is to end. If this determination is negative, the processing returns to step  102  again. If switching into a replay mode has been instructed by operation of the mode switch  56 C or cutting off of the power supply has been instructed by operation of the power switch  56 B, the determination of step  124  is positive and the processing advances to step  126 . In step  126 , through-image display ends, after which the present photography processing ends. 
     As described above, in the digital camera  10  relating to this first exemplary embodiment, if the AF evaluation value when the contrast of the image is maximized is at or below the predetermined threshold Th in the state in which the focusing lens position is fixed by the AF control, the zoom ratio is lowered. Thus, a determination of composition by a photographer when altering a magnification ratio of a subject image and performing photography may be assisted. 
     In this first exemplary embodiment, when the zoom ratio is changed in accordance with the AF evaluation value, a message to that effect, or an icon or the like, may be displayed at the LCD  30 . 
     Second Exemplary Embodiment 
     For the first exemplary embodiment, a mode has been described in which the zoom ratio is lowered if the AF evaluation value when the image contrast is maximized falls to or below the predetermined threshold value Th. For the second exemplary embodiment, a mode will be described in which the zoom ratio is lowered if a comparison value, which is calculated on the basis of AF evaluation values that correspond to a predetermined interval between images acquired via the CCD  14 , is at or below a predetermined threshold value. 
     The structure of a digital camera relating to this second exemplary embodiment is similar to the structure of the digital camera  10  described in the first exemplary embodiment (see  FIG. 1  and  FIG. 2 ), and only the details of the photography processing differ. Herebelow therefore, the same reference numerals are assigned to the same structures and descriptions thereof are not given. Details of the photography processing are described with reference to the drawings. 
       FIG. 6A  and  FIG. 6B  are a flowchart showing a flow of a photography processing program that is executed by the CPU  32  of the digital camera  10  when the photography mode has been set in accordance with the sliding position of the mode switch  56 C. Herebelow, the photography processing relating to the second exemplary embodiment will be described with reference to  FIG. 6A  and  FIG. 6B . 
     First, in step  200 , display of the through-image is commenced. Then, in step  202 , it is determined whether or not an operation signal representing operation of the zoom control  56 E has been inputted. If this determination is positive, the processing advances to step  204 . In step  204 , the zoom lens is moved in accordance with an operation direction and operation amount of the zoom control  56 E, after which the processing advances to step  206 . On the other hand, if the determination in step  202  is negative, the processing advances to step  206  without executing the processing of step  204 . 
     In step  206 , it is determined whether or not an operation signal representing the release button  56 A being put into the half-pressed state has been inputted. If this determination is positive, the processing advances to step  208  and the focusing lens position is fixed, after which the processing advances to step  209 . 
     In step  209 , an acquired AF evaluation value is stored, after which the processing advances to step  210 . In step  210 , it is determined whether or not AF evaluation values corresponding to a predetermined interval have been stored. If this determination is positive, the processing advances to step  211 . In step  211 , a difference between the AF evaluation value that was acquired and stored the predetermined interval before and the AF evaluation value that was most recently acquired and stored is calculated to serve as a comparison value, after which the processing advances to step  212 . In step  212 , it is determined whether or not the calculated comparison value is at or above a pre-specified threshold value (here, the threshold value is positive). If this determination is negative, the processing advances to step  218 , and it is determined whether or not the release button  56 A has been put into the full-pressed state. If the determination in step  218  is positive, the processing advances to step  222 , and photography is implemented by image information provided via the CCD  14  being stored in the recording medium  42 A as still image information. Then, the processing advances to step  224 . 
     Thus, in this second exemplary embodiment, the difference between the AF evaluation value acquired and stored the predetermined interval before and the AF evaluation value acquired and stored immediately before is calculated to serve as the comparison value, and it is judged that the AF evaluation value is falling significantly if this comparison value is at or above the pre-specified threshold value (the threshold value being positive). 
     If the determination of step  218  is negative, the processing advances to step  220 , and it is determined whether or not the half-pressed state of the release button  56 A has been released. If the determination of step  220  is negative, the processing advances to step  216 . If the determination of step  220  is positive, the processing returns to step  202 . 
     Meanwhile, if the determination of step  212  is positive, it is judged that the target to be photographed has been misplaced due to hand shake ( FIG. 4B ), and the processing advances to step  213 . In step  213 , it is determined whether or not the position of the zoom lens is the position at which the viewing angle is maximized (the state in which the subject image is minimally reduced; i.e., the wide angle end). If this determination is negative, the processing advances to step  214  and the zoom lens is moved toward the low magnification end, after which the processing advances to step  216 . If the determination in step  213  is positive, it is judged that hand shake is not a factor at this zoom ratio, and the processing advances to step  218 . 
     Here, when the zoom lens is moved toward the low magnification end, a movement amount may be so as to move the zoom lens toward the wide angle end by a fixed amount, or so as to move the zoom lens to a predetermined position. 
     In step  216 , the AF evaluation value detected by the AF detection circuit  34  in this state is acquired, after which the processing returns to step  209 . 
     In step  224 , it is determined whether or not photography is to end. If this determination is negative, the processing returns to step  202  again. If switching into the replay mode has been instructed by operation of the mode switch  56 C or cutting off of the power supply has been instructed by operation of the power switch  56 B, the determination of step  224  is positive and the processing advances to step  226 . In step  226 , the through-image display ends, after which the present photography processing ends. 
     As described above, in the digital camera  10  relating to this second exemplary embodiment, the zoom ratio is lowered if, in the state in which the focusing lens position is fixed by the focusing control, the comparison value calculated on the basis of the AF evaluation values corresponding to the predetermined interval between images acquired via the CCD  14  is at or below the predetermined threshold. Thus, a determination of composition by a photographer when altering a magnification ratio of a subject image and performing photography may be assisted. 
     Here, a difference between an average value of AF evaluation values corresponding to the predetermined interval and the AF evaluation value acquired and stored most recently may be employed as the comparison value. 
     Further, as shown in  FIG. 7 , when the zoom ratio is to be changed by the zoom lens being moved toward the low magnification end, an amount of the change in the zoom ratio may vary in a stepwise manner with respect to the comparison value. The zoom ratio change amount that corresponds to a comparison value may be determined using a pre-specified table, a function, plural thresholds or the like. 
     That is, as shown in  FIG. 8A  to  FIG. 8E , the comparison value in a case of going from the state shown in  FIG. 8A  to the state shown in  FIG. 8B  is smaller than a comparison value in a case of going from the state shown in  FIG. 8A  to the state shown in  FIG. 8D . Therefore, in the case of going from  FIG. 8A  to  FIG. 8B , there is a high likelihood of the target of photography not being greatly displaced, or of the target of photography being displaced but a subject image included in the photography region being identifiable. Therefore, as shown in  FIG. 8C , even if the zoom ratio is changed a little, a user can easily re-adjust the viewing angle. In contrast, in the case of going from  FIG. 8A  to  FIG. 8D , there is a high likelihood of the target of photography being greatly displaced or of it being difficult to identify a subject included in the photography region because the AF evaluation value is too low. Therefore, as shown in  FIG. 8E , the zoom ratio is greatly changed to facilitate identification of the subject image by the user. 
     In this second exemplary embodiment, when the zoom ratio is changed in accordance with the comparison value, a message to that effect, or an icon or the like, may be displayed at the LCD  30 . 
     Third Exemplary Embodiment 
     For the first exemplary embodiment and the second exemplary embodiment, modes have been described in which the zoom ratio is lowered in accordance with AF evaluation values at which image contrast is maximized. For the third exemplary embodiment, a mode will be described in which, in accordance with change amounts of AF evaluation values of division regions, a display of advice that shows a direction to a subject image to a user is implemented. 
     The structure of a digital camera relating to this third exemplary embodiment is similar to the structure of the digital camera  10  described in the first exemplary embodiment (see  FIG. 1  and  FIG. 2 ), and only the details of the photography processing differ. Herebelow therefore, the same reference numerals are assigned to the same structures and descriptions thereof are not given. Details of the photography processing are described with reference to the drawings. 
       FIG. 9A  and  FIG. 9B  are a flowchart showing a flow of a photography processing program that is executed by the CPU  32  of the digital camera  10  when the photography mode has been set in accordance with the sliding position of the mode switch  56 C. Herebelow, the photography processing relating to the third exemplary embodiment will be described with reference to  FIG. 9A  and  FIG. 9B . 
     First, in step  300 , display of the through-image is commenced. Then, in step  302 , it is determined whether or not an operation signal representing operation of the zoom control  56 E has been inputted. If this determination is positive, the processing advances to step  304 . In step  304 , the zoom lens is moved in accordance with an operation direction and operation amount of the zoom control  56 E, after which the processing advances to step  306 . On the other hand, if the determination in step  302  is negative, the processing advances to step  306  without executing the processing of step  304 . 
     In step  306 , it is determined whether or not an operation signal representing the release button  56 A being put into the half-pressed state has been inputted. If this determination is positive, the processing advances to step  307  and the focusing lens position is fixed, after which the processing advances to step  308 . In step  308 , division regions that are used by the AF function are stored to serve as positions of focusing subjects, after which the processing advances to step  309 . 
     As is shown in  FIG. 10A  to  FIG. 10C , in the present exemplary embodiment, positions and numbers of the division regions that are used by the AF function and the AE function are linked in relation with the size of a focusing subject included in the photography region. That is, as shown in  FIG. 10A , when the zoom ratio is low, positions of the division regions used by the AF function and the AE function are set to positions of the focusing subject, and the number of division regions is set to 4 in accordance with the size of the focusing subject. Then, as the zoom ratio is increased, as shown in  FIG. 10B  and  FIG. 10C , the size of the subject included in the photography region increases, and accordingly the positions of the division regions that are used by the AF function and the AE function are set to positions of the focusing subject and the number of division regions increases in accordance with the size of the focusing subject. 
     In step  309 , AF evaluation values of the regions stored as positions of the focusing subject are respectively stored, after which the processing advances to step  310 . In step  310 , it is determined whether or not AF evaluation values that correspond to a predetermined interval have been stored. If this determination is positive, the processing advances to step  311 . In step  311 , differences between the AF evaluation values that were acquired and stored the predetermined interval before and the AF evaluation values that were most recently acquired and stored are calculated to serve as comparison values, after which the processing advances to step  312 . In step  312 , it is determined whether or not any of the calculated comparison values is at or above a pre-specified threshold value (here, the threshold value is positive). If this determination is negative, the processing advances to step  318 , and it is determined whether or not the release button  56 A has been put into the full-pressed state. If the determination in step  318  is positive, the processing advances to step  322 , and photography is implemented by image information provided via the CCD  14  being stored in the recording medium  42 A as still image information. Then, the processing advances to step  324 . 
     Thus, in this third exemplary embodiment, the differences between the AF evaluation values acquired and stored the predetermined interval before and the AF evaluation values acquired and stored immediately before are calculated to serve as the comparison values, and it is judged that an AF evaluation value is falling significantly if the comparison value thereof is at or above the pre-specified threshold value (the threshold value being positive). 
     If the determination of step  318  is negative, the processing advances to step  320 , and it is determined whether or not the half-pressed state of the release button  56 A has been released. If the determination of step  320  is negative, the processing advances to step  321 . If the determination of step  320  is positive, the processing returns to step  302 . 
     Meanwhile, if the determination of step  312  is positive, it is judged that the target to be photographed has been misplaced due to hand shake ( FIG. 4B ), and the processing advances to step  314 . In step  314 , display of advice recommending that the lens be turned to the direction opposite from the region at which the difference in the AF evaluation value is largest is performed, after which the processing advances to step  318 . 
     If the image obtained via the CCD  14  goes from the state shown in  FIG. 10C  to the stage shown in  FIG. 10D , the region at which the difference in the AF evaluation value is largest is the division region that appears as solid white in  FIG. 10D . In the example shown in  FIG. 10D , an arrow indicating the opposite direction from the region at which the difference in the AF evaluation value is largest is employed as the advice display. 
     In step  321 , the AF evaluation values of the division regions detected by the AF detection circuit  34  in this state are acquired, after which the processing returns to step  309 . 
     In step  324 , it is determined whether or not photography is to end. If this determination is negative, the processing returns to step  302  again. If switching into the replay mode has been instructed by operation of the mode switch  56 C or cutting off of the power supply has been instructed by operation of the power switch  56 B, the determination of step  324  is positive and the processing advances to step  326 . In step  326 , the through-image display ends, after which the present photography processing ends. 
     As described above, in the digital camera  10  relating to this third exemplary embodiment, an AF evaluation value of the image acquired via the CCD  14  is calculated for each of plural division regions, and advice display showing the direction of a subject to the user is performed on the basis of amounts of change of the AF evaluation values of the division regions. Thus, a determination of composition by a photographer when altering a magnification ratio of a subject image and performing photography may be assisted. 
     Note that the constitution of the digital camera  10  described in the above exemplary embodiments (see  FIG. 1  and  FIG. 2 ) and the flows of photography processing (see  FIG. 5 ,  FIG. 6A  and  FIG. 6B ,  FIG. 9A  and  FIG. 9B ) are examples; suitable modifications are applicable within a scope not departing from the spirit of the present invention.