New computer technology is changing lens design from a unique profession to a branch of optical engineering. However, the fundamental problem of optical design remains: the construction of a suitable merit function (mathematical or otherwise) to specify the properties of the optimal design. As the scope of optical design expands, the number and variety of data to be included grow correspondingly. The conventional image quality specifications of an optical design are too simplistic to characterize a lens: tolerances, operating conditions, and manufacturing data must also be included. It is useful to think of optical design as a process of documentation preparation, in which the document consists of the lens data and all the other data needed to construct the merit function.