Automatic focusing apparatus and control method therefor

Abstract

An automatic focusing apparatus detects presence or absence of change in a distance between an object and the automatic focusing apparatus while operating in an operation mode to continuously perform an adjustment of the position of a focus lens to focus on the object, and stops a movement of the focus lens if a change in the distance is not detected.

What is claimed is: 
     
         1 . An imaging apparatus comprising:
 an image sensor configured to capture an image of an object through a photographic system including a focus lens and output image data;   a scan unit configured to move the focus lens within a predetermined scan range, having a scan center position, defined by a scan-starting point and a scan-ending point;   a calculation unit configured to calculate a focus evaluation value based on the image data while the scan unit moves the focus lens, and to determine a maximal focus evaluation value based on the focus evaluation value;   a control unit configured to adjust the focus lens to a lens position where the maximal focus evaluation value was obtained; and   a setting unit configured to set a scan range for a next scan depending on whether a direction of a lens position where the maximal focus evaluation value was obtained in a previous scan to a scan center position of the scan range in the previous scan is the same as a direction of a lens position where the maximal focus evaluation value is obtained in a present scan to a scan center position of the scan range for the present scan, or not.   
     
     
         2 . The imaging apparatus according to  claim 1 , wherein, if the direction of the lens position where the maximal focus evaluation value was obtained in the previous scan to the scan center position of the scan range for the previous scan is not the same as the direction of the lens position where the maximal focus evaluation value is obtained in the present scan to the scan center position of the scan range for the present scan, the scan range for the next scan is set without using a prediction calculation, and
 wherein, the prediction calculation is based on the lens position where the maximal focus evaluation value has been obtained in the previous scan and the lens position where the maximal focus evaluation value is obtained in the present scan.   
     
     
         3 . A method for controlling an imaging apparatus, comprising:
 capturing an image of an object through a photographic system including a focus lens and outputting image data;   moving the focus lens within a predetermined scan range, having a scan center position, defined by a scan-starting point and a scan-ending point;   calculating a focus evaluation value based on the image data while moving the focus lens, and determining a maximal focus evaluation value based on the focus evaluation value;   adjusting the focus lens to a lens position where the maximal focus evaluation value was obtained; and
 setting a scan range for a next scan depending on whether a direction of a lens position where the maximal focus evaluation value was obtained in a previous scan to a scan center position of previous scan is the same as a direction of a lens position corresponding to the maximal focus evaluation value obtained in a present scan to a scan center position of the present scan, or not. 
   
     
     
         4 . An imaging apparatus comprising:
 an image sensor configured to capture an image of an object through a photographic system including a focus lens and output image data;   a scan unit configured to move the focus lens within a predetermined scan range, having a scan center position, defined by a scan-starting point and a scan-ending point;   a calculation unit configured to calculate a focus evaluation value based on the image data while the scan unit moves the focus lens, and to determine a maximal focus evaluation value based on the focus evaluation value;   a control unit configured to adjust the focus lens to a lens position where the maximal focus evaluation value was obtained; and   a setting unit configured to set a scan range for a (N+1)st scan depending on whether a direction of a lens position where the maximal focus evaluation value was obtained in the (N−1)st scan to a scan center position of the scan range for the (N−1)st scan is the same as the direction of a lens position where the maximal focus evaluation value obtained in a Nth scan to the scan center position of the scan range for the Nth scan, or not,   wherein N is a natural number.   
     
     
         5 . The imaging apparatus according to  claim 4 , wherein, if the direction of the lens position where the maximal focus evaluation value was obtained in the (N−1)st scan to the scan center position of the scan range for the (N−1)st scan is not the same as the direction of the lens position where the maximal focus evaluation value is obtained in the Nth scan to the scan center position of the scan range for the Nth scan, the scan range for the (N+1)st scan is not set based on the prediction calculation, and
 wherein, the prediction calculation is based on the lens position where the maximal focus evaluation value has been obtained in the previous scan and the lens position where the maximal focus evaluation value is obtained in the present scan. 
 
     
     
         6 . A method for controlling an imaging apparatus comprising:
 capturing an image of an object through a photographic system including a focus lens and output image data;   moving the focus lens within a predetermined scan range, having a scan center position, defined by a scan-starting point and a scan-ending point;   calculating a focus evaluation value based on the image data while moving the focus lens;   determining a maximal focus evaluation value based on the focus evaluation value;   adjusting the focus lens to a lens position where the maximal focus evaluation value was obtained; and   setting a scan range for a (N+1)st scan depending on whether a direction of a lens position where the maximal focus evaluation value was obtained in the (N−1)st scan to a scan center position of the scan range for the (N−1)st scan is the same as the direction of a lens position where the maximal focus evaluation value obtained in a Nth scan to the scan center position of the scan range for the Nth scan, or not,   wherein N is a natural number.