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.

1 . An automatic focusing apparatus comprising:
 an imaging unit configured to capture an object image that is input via a focus lens to output image data;   a detection unit configured to detect a focus signal that indicates a focusing state of the focus lens based on the image data;   a focus adjustment unit configured to adjust a position of the focus lens based on the focus signal detected by the detection unit;   a control unit configured to cause the focus adjustment unit to operate in an operation mode to continuously perform an adjustment of the position of the focus lens; and   a distance change detection unit configured to detect, when the focus adjustment unit is operating in the operation mode, presence or absence of change in a distance between the object and the automatic focusing apparatus,   wherein the control unit stops the adjustment of the position of the focus lens if a change in the distance is not detected by the distance change detection unit.   
     
     
         2 . The automatic focusing apparatus according to  claim 1 , wherein the control unit resumes the adjustment of the position of the focus lens if a change in the distance is detected by the distance change detection unit after stopping the adjustment of the position of the focus lens. 
     
     
         3 . The automatic focusing apparatus according to  claim 1 , wherein the distance change detection unit detects the presence or absence of change in the distance between the object and the automatic focusing apparatus based on an amount of change in a focus signal continuously acquired while the focus adjustment unit is operating in the operation mode. 
     
     
         4 . The automatic focusing apparatus according to  claim 1 , further comprising a luminance acquisition unit configured to acquire a luminance value of the object based non the image data,
 wherein the distance change detection unit detects the presence or absence of change in the distance between the object and the automatic focusing apparatus based on an amount of change in a luminance value continuously acquired by the luminance acquisition unit while the focus adjustment unit is operating in the operation mode.   
     
     
         5 . The automatic focusing apparatus according to  claim 1 , further comprising a first movement amount detection unit configured to compare, in time series, the image data continuously acquired while the focus adjustment unit is operating in the operation mode to detect an amount of movement of the object,
 wherein the distance change detection unit detects the presence or absence of change in the distance between the object and the automatic focusing apparatus based on the amount of movement of the object detected by the first movement amount detection unit.   
     
     
         6 . The automatic focusing apparatus according to  claim 1 , further comprising a face detection unit configured to detect a face region of a person included in the image data based on the image data,
 wherein the distance change detection unit detects the presence or absence of change in the distance between the object and the automatic focusing apparatus based on a size change of the face region continuously acquired by the face detection unit while the focus adjustment unit is operating in the operation mode.   
     
     
         7 . The automatic focusing apparatus according to  claim 1 , further comprising a second movement amount detection unit configured to detect an amount of movement of the automatic focusing apparatus,
 wherein the distance change detection unit detects the presence or absence of change in the distance between the object and the automatic focusing apparatus based on the amount of movement of the automatic focusing apparatus detected by the second movement amount detection unit.   
     
     
         8 . The automatic focusing apparatus according to  claim 1 , wherein the distance change detection unit detects that there is no change in the distance between the object and the automatic focusing apparatus if a case where a position of the focus lens at which the focus signal becomes maximal is included within a range set in advance relative to a reference position determined based on a latest adjustment result by the focus adjustment unit is repeated a predetermined number of times. 
     
     
         9 . A method for controlling an automatic focusing apparatus including a focus adjustment unit configured to calculate a focus evaluation value that indicates a contrast of a predetermined focus detection area based on image data of an image of an object formed and captured by a photographic optical system including a focus lens, and to adjust a position of the focus lens so that the focus evaluation value becomes maximal, and a control unit configured to cause the focus adjustment unit to operate in an operation mode to continuously perform an adjustment of the position of the focus lens, the method comprising:
 detecting presence or absence of change in a distance between the object and the automatic focusing apparatus when the focus adjustment unit is operating in the operation mode; and   stopping the adjustment of the position of the focus lens if a change in the distance is not detected.