Method of automatically focusing using a quadratic function in camera

1231232 1 3 2 A method of automatically focusing a camera determines a position of a focus lens where an amount of a high frequency in an image signal is a maximum. The amount of a high frequency included in an image signal is measured at intervals of multiple focus motor steps. Three of the measured positions (x, x, x) and their corresponding measured high frequency amounts (y, y, y) are identified, where yis the largest of the measured high frequency amounts, and xand xare the nearest measured positions on either side of x. A quadratic function f(x) is determined for the high frequency amount with respect to the focus lens position x. A position at which a derivative of the quadratic function f(x) is zero, is determined to be the position corresponding to maximum high frequency amount. Thus, the driving time of the focus motor can be reduced.