Abstract:
An apparatus, such as a focus adjusting apparatus, includes a focus adjusting system, a driving device which drives the focus adjusting system from one of a state in which a near-distance object is in focus and a state in which a far-distance object is in focus to the other, and a control device which repeatedly performs determination of a focusing state of the focus adjusting system while causing the driving device to drive the focus adjusting system, and, if the focus adjusting system has been driven in one direction until the number of times of the determination repeatedly performed reaches a predetermined number of times, restrains the focus adjusting system from being driven in the one direction, so that a focus adjusting operation can be appropriately performed.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a focus adjusting apparatus and a focus adjusting method for use in a variety of video cameras, etc.  
         [0003]     2. Description of Related Art  
         [0004]     In recent years, video apparatuses such as video cameras have made remarkable progress and are ordinarily provided with an automatic focusing control function, an automatic iris control function, a zooming function, etc., so that the improvements of operability and the increase of functions have been attempted in every part thereof.  
         [0005]     With regard to an automatic focusing apparatus, the main trend of nowadays is to use such a method that focus adjustment is performed by detecting, as an AF evaluation value, the sharpness of an image plane from within a video signal obtained by photoelectrically converting an object image with an image sensor or the like, and controlling the position of a focusing lens in such a way as to make the AF evaluation value maximum.  
         [0006]     The above-mentioned AF evaluation value is obtained generally by using the level of a high-frequency component of video signal extracted by a band-pass filter for a certain pass band, or the like. In a case where an ordinary object is taken for image pickup, the AF evaluation value becomes larger accordingly as a picked-up image becomes sharper, as shown in  FIG. 2 , and a point at which the level of the AF evaluation value becomes maximum is determined to be an in-focus point.  
         [0007]     In the case of a practical video camera, as shown in  FIG. 1 , an AF microcomputer  115  performs an automatic focus adjusting operation by causing a focusing lens  105  to move in such a way as to make the output signal level of an AF evaluation value processing circuit  114  maximum.  
         [0008]     Then, as shown in  FIG. 3 , the AF microcomputer  115  performs a minute driving action on the focusing lens  105 , and if an in-focus state is determined to have been attained, performs an in-focus processing operation. When no in-focus state is determined to have been attained, if a direction according to which the AF evaluation value becomes larger has been determined, the AF microcomputer  115  drives the focusing lens  105  in that direction, i.e., performs the so-called hill-climbing driving action. When the focusing lens  105  has reached such a position as to correspond to the peak of the AF evaluation value, the AF microcomputer  115  again performs the minute driving action on the focusing lens  105 . After that, if an in-focus state is determined to have been attained, the AF microcomputer  115  makes a comparison between the AF evaluation value obtained at that time and the newest AF evaluation value. If a difference between the two AF evaluation values is found to be greater than a predetermined level, the AF microcomputer  115  decides that the driving of the focusing lens  105  be re-started, and performs the minute driving action on the focusing lens  105 .  
         [0009]     The conventional minute driving action will be described below with reference to  FIG. 9 . Referring to  FIG. 9 , which is a flow chart showing a processing operation of the AF microcomputer  115  for the minute driving action, the processing operation starts in step S 901 . In step S 902 , an AF evaluation value is taken in from the AF evaluation value processing circuit  114 . In step S 903 , a check is made to find if the AF evaluation value taken in step S 902  is larger than an AF evaluation value taken in for the last time. If not, i.e., if the AF evaluation value taken in step S 902  is smaller than the AF evaluation value taken in for the last time, the flow proceeds to step S 904 . If so, i.e., if the AF evaluation value taken in step S 902  is larger than the AF evaluation value taken in for the last time, the flow proceeds to step S 905 . In step S 904 , the focusing lens  105  is driven by a predetermined amount in a direction reverse to the direction in which the focusing lens has been driven for the last time. On the other hand, in step S 905 , the focusing lens  105  is driven by the predetermined amount in the same direction as the direction in which the focusing lens  105  has been driven for the last time.  
         [0010]     In step S 906 , a check is made to find if the direction for driving the focusing lens  105  has been determined continuously for a predetermined number of times to be the same direction. If so, i.e., if the focusing lens  105  has been driven in the same direction continuously for the predetermined number of times, the flow proceeds to step S 907 . If not, i.e., if the focusing lens  105  has not been driven in the same direction continuously for the predetermined number of times, the flow proceeds to step S 908 . In step S 908 , a check is made to find if the focusing lens  105  remains in the same area for a predetermined period of time, i.e., if the lens position stays within a predetermined range for a predetermined period of time. If so, the flow proceeds to step S 909 . If not, the flow proceeds to step S 910  to bring the processing operation to an end. In step S 907 , it is considered that the determination of the direction has been attained, and, then, the flow proceeds to step S 910  to bring the processing operation to an end. In step S 909 , it is considered that the determination of an in-focus state has been attained, and, then, the flow proceeds to step S 910  to bring the processing operation to an end.  
         [0011]     As described above, while repeatedly performing the decision of re-starting→the minute driving→the hill-climbing driving→the minute driving→the decision of re-starting, the AF microcomputer  115  causes the focusing lens  106  to move in such a way as to always make the AF evaluation value maximum.  
         [0012]     However, the above-described conventional focus adjusting apparatus has the following drawbacks.  
         [0013]     Since the AF evaluation value is generally the level of a high-frequency component of a video signal extracted by a band-pass filter having a certain pass band, the peak level of the AF evaluation value obtained at an in-focus point does not become constant with respect to individual objects for image pickup.  
         [0014]     Thus, there is a possibility that, even if the AF evaluation values for the respective objects are the same value, one object is in focus and the other object is out of focus.  
         [0015]     Therefore, for example, when the luminance level of an object has changed, even if the AF evaluation value is increasing with the focusing lens being moved, in some cases, an image of the object is blurred in reality. Then, if the focusing lens remains being moved in the same direction, considering that the AF evaluation value is increasing, the image of the object would become conspicuously blurred.  
       BRIEF SUMMARY OF THE INVENTION  
       [0016]     In accordance with one aspect of the invention, there is provided an apparatus, such as a focus adjusting apparatus, comprising a focus adjusting system, a driving device which drives the focus adjusting system from one of a state in which a near-distance object is in focus and a state in which a far-distance object is in focus to the other, and a control device which repeatedly performs determination of a focusing state of the focus adjusting system while causing the driving device to drive the focus adjusting system, and, if the focus adjusting system has been driven in one direction until the number of times of the determination repeatedly performed reaches a predetermined number of times, restrains the focus adjusting system from being driven in the one direction, so that a focus adjusting operation can be appropriately performed.  
         [0017]     In accordance with another aspect of the invention, there is provided a focus adjusting method comprising the steps of repeatedly performing determination of a focusing state of a focus adjusting system while driving the focus adjusting system from one of a state in which a near-distance object is in focus and a state in which a far-distance object is in focus to the other, and, if the focus adjusting system has been driven in one direction until the number of times of the determination repeatedly performed reaches a predetermined number of times, restraining the focus adjusting system from being driven in the one direction, so that a focus adjusting operation can be appropriately performed.  
         [0018]     The above and further aspects and features of the invention will become apparent from the following detailed description of a preferred embodiment thereof taken in conjunction with the accompanying drawings.  
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
       [0019]      FIG. 1  is a block diagram showing the arrangement of a video camera according to an embodiment of the invention.  
         [0020]      FIG. 2  is a diagram showing the relationship between the position of a focusing lens and a focus voltage level.  
         [0021]      FIG. 3  is a flow chart showing a main AF processing operation in the embodiment.  
         [0022]      FIG. 4  is a flow chart showing a minute driving action in the embodiment.  
         [0023]      FIG. 5  is a diagram showing the position of the focusing lens relative to the lapse of time.  
         [0024]      FIG. 6  is a flow chart showing a hill-climbing driving action in the embodiment.  
         [0025]      FIG. 7  is a diagram showing the movement of the focusing lens in the embodiment.  
         [0026]     FIGS.  8 ( a ) and  8 ( b ) are diagrams for comparison between the movement positions of the focusing lens.  
         [0027]      FIG. 9  is a flow chart showing a conventional minuter driving action. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0028]     Hereinafter, a preferred embodiment of the invention will be described in detail with reference to the drawings.  
         [0029]      FIG. 1  is a block diagram showing the arrangement of a video camera according to the embodiment of the invention. In  FIG. 1 , reference numeral  101  denotes a first fixed lens group, reference numeral  102  denotes a variator lens for varying magnification, reference numeral  103  denotes an iris, reference numeral  104  denotes a second fixed lens group, and reference numeral  105  denotes a focusing-compensation lens (hereinafter referred to as the focusing lens) having both the function of compensating for the shift of a focal plane caused by the variation of magnification and the function of focusing.  
         [0030]     Reference numeral  106  denotes a CCD (charge-coupled device) serving as an image sensor, and reference numeral  107  denotes an AGC (automatic gain control) for amplifying the output of the CCD  106 , the amplification factor of which is controlled by the output signal of an AF microcomputer  115  (to be described later). Reference numeral  108  denotes a camera signal processing circuit. Reference numerals  110  and  112  denote actuators (motors) for respectively moving the variator lens  102  and the focusing lens  105 , and reference numerals  111  and  113  denote drivers for respectively driving the actuators  110  and  112  in accordance with the output signals of the AF microcomputer  115 .  
         [0031]     Reference numeral  114  denotes an AF evaluation value processing circuit for extracting, as a focus voltage level (AF evaluation value) shown in  FIG. 2 , a high-frequency component for focus detection from the output signal of the image sensor  106 , and reference numeral  115  denotes the AF microcomputer for collectively controlling the entirety of the video camera and for controlling the actuators  110  and  112  on the basis of the output of the AF evaluation value processing circuit  114 .  
         [0032]     In the video camera having the above-described construction, the AF microcomputer  115  performs a focus adjusting operation by causing the motor  112  and the driver  113  to move the focusing lens  105  in an optical axis direction in such a way as to make the AF evaluation value maximum. Then, the AF microcomputer  115  determines a direction in which the focusing lens  105  is so moved as to increase the AF evaluation value, by making a comparison between AF evaluation values respectively obtained before and after the focusing lens  105  is moved by a predetermined amount, and causes the focusing lens  105  to move in the thus-determined direction by the predetermined amount at each time. If the thus-determined direction is the same continuously for a predetermined number of times, the AF microcomputer  115  inhibits the focusing lens  106  from being moved in that direction, and reverses the moving direction of the focusing lens  105 .  
         [0033]     A control operation to be performed by the AF microcomputer  115  will be described in detail with reference to FIGS.  3  to  7 . First, referring to  FIG. 3 , which is a flow chart showing a main AF processing operation, the processing operation starts in step S 301 . In step S 302 , a minute driving action is performed to determine whether an in-focus state is attained, or, if an in-focus state is not attained, in which direction an in-focus point is located. The details of the minute driving action are described later. In step S 303 , a check is made to find if an in-focus state has been attained in step S 302 . If so, the flow proceeds to step S 309 . If not, the flow proceeds to step S 304 .  
         [0034]     In step S 304 , a check is made to find if the determination of the direction has been attained in step S 304 . If so, the flow proceeds to step S 305 , where a hill-climbing driving action is performed. If not, the flow returns to step S 302 , where the minute driving action is continued. In the hill-climbing driving action in step S 305 , the focusing lens  105  is driven at high speed in such a direction as to increase the AF evaluation value in the so-called hill-climbing manner. The details of the hill-climbing driving action are described later.  
         [0035]     In step S 306 , a check is made to find if the AF evaluation value has passed across a peak thereof in step S 305 . If so, the flow proceeds to step S 307 . If not, the flow returns to step S 305 , where the hill-climbing driving action is continued. In step S 307 , the focusing lens  105  is made to return to the position corresponding to the peak of the AF evaluation value obtained in the hill-climbing driving action. In step S 308 , a check is made to find if the focusing lens  105  has returned to the position corresponding to the peak of the AF evaluation value. If so, the flow returns to step S 302 , where the minute driving action is again performed. If not, the flow returns to step S 307 , where the operation for causing the focusing lens  105  to return to the position corresponding to the peak is continued.  
         [0036]     Next, the focusing operation to be performed from step S 309  is described. In step S 309 , the AF evaluation value is memorized. In step S 310 , the AF evaluation value memorized in step S 309  and the newest AF evaluation value are compared with each other, and, if a difference therebetween is found to be larger than a predetermined level, it is decided that the driving of the focusing lens  105  be re-started. In step S 311 , a check is made to find if it has been decided that the driving of the focusing lens  105  be re-started in step S 310 . If so, the flow returns to step S 302 , where the minute driving action is started again. If not, the flow proceeds to step S 312 . In step S 312 , the focusing lens  105  is brought to a stop, and the flow returns to step S 310 , where the decision of the re-start of the focusing lens  105  is continued.  
         [0037]     Here, the minute driving action (low-speed driving action) to be performed in the above step S 302  is described in detail with reference to Fig.  FIG. 4 , which is a flow chart showing the control operation of the AF microcomputer  115 . The control operation shown in  FIG. 4  corresponds to that shown in  FIG. 9  described in the foregoing with regard to the conventional minute driving action. In  FIG. 4 , steps similar to those shown in  FIG. 9  are denoted by the same step numbers as in  FIG. 9 .  
         [0038]     In the minuter driving action shown in  FIG. 4 , the processing operation starts in step S 901 . In step S 902 , an AF evaluation value is taken in from the AF evaluation value processing circuit  114 . In step S 903 , a check is made to find if the AF evaluation value taken in step S 902  is larger than an AF evaluation value taken in for the last time. If not, i.e., if the AF evaluation value taken in step S 902  is smaller than the AF evaluation value taken in for the last time, the flow proceeds to step S 904 . If so, i.e., if the AF evaluation value taken in step S 902  is larger than the AF evaluation value taken in for the last time, the flow proceeds to step S 401 .  
         [0039]     In step S 401 , a check is made to find if the focusing lens  105  has been moved in the same direction continuously for a predetermined number of times. If so, the flow proceeds to step S 904 . If not, the flow proceeds to step S 905 . In step S 904 , the focusing lens  105  is driven by a predetermined amount in a direction reverse to the direction in which the focusing lens has been driven for the last time. In step S 905 , the focusing lens  105  is driven by the predetermined amount in the same direction as the direction in which the focusing lens  105  has been driven for the last time. In other words, when the focusing lens  105  has been moved in the same direction for the predetermined number of times or more, even if the AF evaluation value is increasing, the direction in which to drive the focusing lens  105  is reversed. By this arrangement, in a case where an object is varied to cause an increase of the AF evaluation value, it is possible to prevent the focusing lens  105  from being erroneously moved in such a direction as to make an image of the object blurred.  
         [0040]     In step S 906 , a check is made to find if the direction for driving the focusing lens  105  has been determined continuously for a predetermined number of times to be the same direction. If so, i.e., if the focusing lens  105  has been driven in the same direction continuously for the predetermined number of times, the flow proceeds to step S 907 . If not, i.e., if the focusing lens  105  has not been driven in the same direction continuously for the predetermined number of times, the flow proceeds to step S 908 . In step S 908 , a check is made to find if the focusing lens  105  remains in the same area for a predetermined period of time, i.e., if the lens position stays within a predetermined range for a predetermined period of time. If so, the flow proceeds to step S 909 . If not, the flow proceeds to step S 910  to bring the processing operation to an end. In step S 907 , it is considered that the determination of the direction has been attained, and, then, the flow proceeds to step S 910  to bring the processing operation to an end. In step S 909 , it is considered that the determination of an in-focus state has been attained, and, then, the flow proceeds to step S 910  to bring the processing operation to an end.  
         [0041]     The position of the focusing lens  105  relative to the lapse of time in the above-described control operation is illustrated in  FIG. 5 . Referring to  FIG. 5 , an AF evaluation value A obtained from electric charges accumulated in the CCD  106  during a period of time A is taken in at a point of time T A , and an AF evaluation value B obtained from electric charges accumulated in the CCD  106  during a period of time B is taken in at a point of time T B . At the point of time T B , the AF evaluation values A and B are compared with each other, and if A&lt;B, the focusing lens  105  is moved in the same direction. On the other hand, if A&gt;B, the focusing lens  105  is made to be moved in the reverse direction.  
         [0042]     Next, the hill-climbing driving action (high-speed driving action) to be performed in steps S 305  and S 306  is described with reference to  FIG. 6 . In the flow chart of  FIG. 6 , the processing operation starts in step S 601 . In step S 602 , an AF evaluation value is taken in from the AF evaluation value processing circuit  114 . In step S 603 , a check is made to find if the AF evaluation value taken in step S 602  is larger than an AF evaluation value taken in for the last time. If so, i.e., if the AF evaluation value taken in step S 602  is larger than the AF evaluation value taken in for the last time, the flow proceeds to step S 604 . If not, i.e., if the AF evaluation value taken in step S 602  is smaller than the AF evaluation value taken in for the last time, the flow proceeds to step S 605 .  
         [0043]     In step S 604 , the focusing lens  105  is driven at a predetermined speed in the same direction as that for the last time, and the flow returns to step S 602 . In step S 605 , a check is made to find if the AF evaluation value has passed across a peak thereof. If the AF evaluation value has decreased without passing across any peak thereof, the flow proceeds to step S 606 . If the AF evaluation value has decreased after passing across a peak thereof, the flow proceeds to step S 607  to bring the processing operation to an end. In step S 606 , the focusing lens  105  is driven at the predetermined speed in the direction reverse to that for the last time, and the flow returns to step S 602 .  
         [0044]     The movement of the focusing lens  105  in respect of the AF evaluation value in the above control operation is illustrated in  FIG. 7 . Referring to  FIG. 7 , in the case of a locus A, since the AF evaluation value is decreasing after passing across a peak thereof, it is considered that an in-focus point exists, and the hill-climbing driving action is ended and the minute driving action is started. On the other hand, in the case of a locus B, since the AF evaluation value is decreasing without passing across any peak thereof, it is considered that the direction for driving the focusing lens  105  is erroneous, and the direction for driving the focusing lens  105  is reversed and the hill-climbing driving action is continued.  
         [0045]     It is to be noted that the processing operations shown in  FIGS. 3, 4  and  6  are executed by the instructions of the AF microcomputer  115  on the basis of programs which are beforehand stored in a ROM (not shown).  
         [0046]     As has been described above, in the minute driving action, when the AF evaluation value is increasing, the conventional control method would cause the focusing lens  105  to continue moving in the same direction with the processing operation of step S 902 →step S 903 →step S 905 . On the other hand, in the control method according to the embodiment of the invention, if the processing operation of step S 902 →step S 903 →step S 401 →step S 905  has been performed continuously for a predetermined number of times, after that, the processing operation of step S 902 →step S 903  step S 401 →step S 904  is performed. Thus, by once reversing the driving direction of the focusing lens  105  in a case where the focusing lens  105  has been moved continuously in the same direction, it is possible to prevent the driving direction of the focusing lens  105  from being erroneously determined due to a change in the AF evaluation value caused by the variation of an object.  
         [0047]     The above movement of the focusing lens  105  is further explained with reference to FIGS.  8 ( a ) and  8 ( b ). In a case where the AF evaluation value is increasing regardless of the movement of the focusing lens  102 , according to the conventional control method, the processing operation of step S 902 →step S 903 →step S 905  is performed, so that the focusing lens  105  would continue being moved in the same direction, as shown in  FIG. 8 ( a ). On the other hand, according to the embodiment of the invention, if the processing operation of step S 902 →step S 903 →step S 401 →step S 905  has been performed continuously three times, after that, the processing operation of step S 902 →step S 903 →step S 401 →step S 904  is performed. Accordingly, it becomes possible to cause the focusing lens  105  to stay at a particular position as shown in  FIG. 8 ( b ), so that a reliable focus adjusting operation can be performed.  
         [0048]     Thus, according to the embodiment of the invention, by once reversing the driving direction of the focusing lens  105  in a case where the focusing lens  105  has been moved continuously in the same direction, it is possible to prevent the driving direction of the focusing lens  105  from being erroneously determined due to a change in the AF evaluation value caused by the variation of an object. For example, in a case where the AF evaluation value is increasing regardless of the movement of the focusing lens  102 , according to the conventional control method, the focusing lens  105  would be continuously moved in the same direction as shown in  FIG. 8 ( a ). On the other hand, according to the embodiment of the invention, it becomes possible to cause the focusing lens  105  to stay at a particular position as shown in  FIG. 8 ( b ), so that a reliable focus adjusting operation can be performed.  
         [0049]     As has been described in the foregoing, according to the embodiment of the invention, by once reversing the driving direction of the focusing lens  105  in a case where the focusing lens  105  has been moved continuously in the same direction, it is possible to prevent the driving direction of the focusing lens  105  from being erroneously determined due to a change in the AF evaluation value caused by the variation of an object, so that a reliable focus adjusting operation can be performed.  
         [0050]     The individual components shown in schematic or block form in the drawings are all well-known in the camera arts and their specific construction and operation are not critical to the operation or best mode for carrying out the invention.  
         [0051]     While the present invention has been described with respect to what is presently considered to be the preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiment. To the contrary, the invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.  
         [0052]     For example, in the above-described embodiment, when the lens has been minutely driven continuously in the same direction, the lens is made to be driven in the reverse direction. However, the driving of the lens in the same direction may be restrained in various fashions other than the driving in the reverse direction, such as the slowing of the driving speed of the lens, the stopping of the driving of the lens, etc.  
         [0053]     Further, in the above-described embodiment, when the lens has been driven continuously in the same direction during the minute driving action, the lens is made to be driven in the reverse direction. However, the invention is applicable to any driving action other than the minute driving action.  
         [0054]     Further, a focus adjusting system in the above-described embodiment is a type for adjusting focus by moving the lens. However, the invention is applicable to other types of focus adjusting systems, such as a type for adjusting focus by moving the image pickup plane.  
         [0055]     Further, the software arrangement and the hardware arrangement in the above-described embodiment may be adaptively replaced with each other.  
         [0056]     Further, in the invention, the technical elements of the above-described embodiment may be combined with each other according to necessity.  
         [0057]     Further, the invention also applies to cases where each claim or the whole or a part of the arrangement of the embodiment constitutes one apparatus or is used in combination with another apparatus or as a component element of an apparatus.  
         [0058]     Further, the invention is also applicable to various types of cameras, such as an electronic still camera, a video camera and a camera using a silver-halide film, various image pickup apparatuses other than cameras, various optical apparatuses, such as a lens barrel, and other types of apparatuses, and, moreover, to apparatuses adapted for the cameras, the image pickup apparatuses, optical apparatuses and the other types of apparatuses, a method, a computer program product, such as a storage medium, having the method stored therein, and elements constituting the above-mentioned apparatuses, the method or the computer program product.