A built-in self-calibration system and method for a micro-mirror array device, for example, operating as a variable focal length lens is described. The calibration method comprises determining a capacitance value for each micro-mirror element in the array device at a number of predetermined reference angles to provide a capacitance-reference angle relationship. From the capacitance values, an interpolation step is carried to determine intermediate tilt angles for each micro-mirror element in the array. A voltage sweep is applied to the micro-mirror array and capacitance values, for each micro-mirror element in the array, are measured. For a capacitance value that matches one of the values in the capacitance-reference angle relationship, the corresponding voltage is linked to the associated tilt angle to provide a voltage-tilt angle characteristic which then stored in a memory for subsequent use.