Image capturing device and auto-focus method for same

An auto-focus method of an image capturing device comprising the steps of:

• (a) moving a taking lens to a number of positions and capturing an image of an object when the taking lens is located at each of the positions associated therewith;
• (b) comparing the definition of the images of the object to choose the clearest image therefrom and determining the position of the taking lens associated with the clearest image as an in-focus position of the taking lens;
• (c) judging whether the object is moved after the in-focus position of the taking lens is determined;
• and
• (d) repeating the steps (a) and (b) to determine an updated in-focus position of the taking lens and moving the taking lens to the updated in-focus position if the object is moved.

An image capturing device comprising:

• a taking lens movable relative to the image sensor at a plurality of positions;
• an image sensor for capturing an image of an object when the taking lens is located at each of the positions;
• an image processing unit for comparing the definition of the images to chose a clearest image therefrom and determining the position associated with the clearest image as an in-focus position of the taking lens;
• a taking lens driving unit for moving the taking lens to the in-focus position;
• and
• a comparing unit for comparing the definition of an image captured after the in-focus position is determined with that of the clearest image so as to judge whether the object is moved after the in-focus position is determined, and determining an updated in-focus position of the taking lens if the object is moved after the in-focus position is determined.