There are now quite a few good books on optical design, although curiously there are not so many available on computer-aided optical design. The following is a short list of titles that are especially recommended for OSLO users.
Bruce Walker, "Optical Engineering Fundamentals", SPIE Press Vol. TT30, 1997. This is a general introduction to what might be called traditional optical engineering. It is highly readable and relevant to OSLO users because many of its examples are illustrated using (an old version of) OSLO. The data for several of the examples from the book are supplied in the OSLO lens database.
Warren J. Smith, "Modern Optical Engineering (Second Edition)", McGraw-Hill 1990, ISBN 0-07-059174-1. Also "Modern Lens Design", co-authored with Genesee Optics Software (now Sinclair Optics), McGraw-Hill 1992, ISBN 0-07-059178-4. The first of these has been the standard reference in optical engineering since its first edition was published thirty years ago. If you are able to have only one book on optical engineering, this is the one to have. The second book is more specific to lens design. It describes several of the the lenses contained in the OSLO lens database. It is one of the few places where computer optimization is discussed. Both books are used in Warren Smith’s Modern Lens Design courses.
Robert R. Shannon, "The Art and Science of Optical Design", Cambridge University Press 1997, ISBN 0-521-58868-5. This is a new book that surveys the overall design of image-forming systems, including elementary theory and several examples that show the use of three contemporary optical design programs (one of which is OSLO). The book is an outgrowth of lens design classes taught by the author at the Optical Sciences Center, University of Arizona.
W.T. Welford, "Aberrations of Optical Systems", Adam Hilger 1986, ISBN 0-85274-564-8. This is a more formal description of the theory underlying many of the algorithms used in OSLO. For many years this book was used as a text in the first-year graduate course in geometrical optics at The Institute of Optics, University of Rochester.
A. Walther, "The Ray and Wave Theory of Lenses", Cambridge University Press 1995, ISBN 0-521-45. This is the way geometrical optics should be taught (unfortunately it is not). The book is highly recommended to all who really want to understand how their designs work. While the narrative assumes a level of mathematical competence that will strain the abilities of many optical designers, the author’s felicitous style and penchant for compartmentalization make it quite readable.
Max Born and Emil Wolf, "Principles of Optics", Pergamon Press, ISBN 0-08-018018 3. This is the standard reference for classical optics. It should be a part of every optics library. Although it does not deal with computer algorithms or numerical analysis, it covers most of the optical principles used in OSLO.