An optical system is provided, including a movable part, a fixed part, a first sensor, a second sensor, and a control unit, wherein an optical element is disposed on the movable part. The first and second sensors detect the movement of the movable part relative to the fixed part in a first dimension and a second dimension, and thus they respectively generate a first sensing value and a second sensing value. The control unit generates an error value according to the first sensing value and an error curve, and then calibrates the second sensing value according to the error value.