Without doubt, this is the best general survey of optical engineering, in or out of print. The book shows both the author's broad experience as well as his ability to apply theory to practice. The book is far superior in its selection of topics and in clarity and accuracy of presentation to the alternatives, particularly Shannon's book. The book is useful for engineers or scientists from other fields who need to learn some optics, and for experienced practitioners who need a reference and refresher on particular topics. For example, try to calculate the spectral radiance of a blackbody at a particular wavelength and temperature using the formula in your college physics text, then see how Smith treats the same topic; if you got within an order of magnitude of Smith's correct answer from the college text, give yourself a gold star. The second edition's only weakness was its sparse references; I haven't seen the third edition so this may have been improved. However, this still puts Smith's book ahead of Shannon's, which has no references whatever. If you only buy one book on optics, this should be it.