1. Field of the Invention
The present invention relates to a focus adjustment apparatus and a focus adjustment method. More specifically, the present invention relates to an automatic focusing technique.
2. Description of the Related Art
According to a conventional method, an electronic still camera (or video camera) can perform automatic focusing (hereinafter, referred to as “AF”) processing by setting an in-focus position to a lens position where a high frequency component of a luminance signal obtained from an image sensor using a charge coupled device (CCD) can be maximized.
A conventional scan method includes storing a focus evaluation value based on a high frequency component of a luminance signal obtained from the image sensor while driving the lens in each scanning and designating a lens position corresponding to a maximum value of the stored value as an in-focus position.
As another method, a hill-climbing (hereinafter, referred to as “continuous AF”) method includes moving a lens in a predetermined direction so as to increase the focus evaluation value and designating a position where the focus evaluation value can be maximized as an in-focus position.
As discussed in Japanese Patent No. 04106485, the time consumed for an AF operation can be reduced by performing the continuous AF processing so as to keep an in-focus state before instructing preparation for a shooting operation, because a moving range of the focusing lens in an AF scan operation to be performed in response to the shooting preparation instruction can be reduced effectively.
In the above-described continuous AF processing, if the lens is moved in the predetermined direction to increase the focus evaluation value, an object to be photographed may not be quickly focused in a case where a region to be focused on the image plane is not identified.
According to the method discussed in Japanese Patent No. 04106485, the continuous AF processing is performed in combination with the scan processing to quickly accomplish the focusing operation. However, in this case, a target object to be focused (hereinafter, referred to as a “main object”) is not identified on the image plane to be focused by a user. Therefore, there may be a shooting scene in which the main object cannot be focused.