US Patent 7443772 Focus offset calibration

A series of signals is applied to a lens actuator of a disc media marking device to respectively position a lens at a series of distances from an optical disc. A mark is formed on the optical disc at each of the distances of the lens from the optical disc by passing a light beam through the lens and onto the optical disc. The darkest of the marks is determined. The signal applied to the actuator corresponding to the darkest mark is determined.