1. A method for focusing a lens, comprising the steps of: setting a focus sampling frequency to a first sampling frequency and setting a shutter speed to a first shutter speed; determining a first amount of light passing through the focusing lens; determining a first focus evaluation value using the first amount of light passing through the focusing lens; changing a position of the focusing lens by driving a motor by an amount calculated using the first focus evaluation value; changing at least one of the focus sampling frequency and the shutter speed when the first focus evaluation value is greater than a reference value; determining a second amount of light passing through the focusing lens, after the step of changing said at least one of the focus sampling frequency and the shutter speed; determining a second focus evaluation value using the second amount of light passing through the focusing lens; and changing a position of the focusing lens by driving the motor by an amount calculated using the second focus evaluation value and a previously determined focus evaluation value.