Abstract: A method includes: a) measuring individual parts K1-KN of an optical system to provide measurement data, N being greater than one; b) using the measurement data to virtualize the individual parts K1-KN and using the virtualized individual parts K1-KN to generate an actual assembly model by geometrically stringing together a plurality of the virtualized individual parts K1-KN, the actual assembly model comprising virtual actual positions of the virtualized individual parts K1-KN in a virtually assembled state; c) using the actual assembly model and a target assembly model to determine a correction measure, the target assembly model comprising virtual target positions of one or more of the virtualized individual parts K1-KN in the virtually assembled state; and d) using the correction measure, assembling the individual parts K1-KN to form the optical system.