A method of characterizing an optical system of a laser processing system includes directing an energy beam through a plurality of portions of a sample by adjusting an orientation of an adjustable beam redirection element of the optical system in accordance with a predetermined movement pattern to form a plurality of test patterns in the sample at each portion. The optical system comprises an imaging system having an expected focal position. In the movement pattern, the energy beam is directed in a plurality of different directions in the sample in the formation of each test pattern. At least two of the plurality of test patterns are formed at different calibration distances from an expected focal position of the optical system. An accuracy of the expected focal position is determined by detecting a level of modification in the sample caused by the energy beam at the plurality of test patterns.