Another essential guide to many aspects of the optics encountered in amateur astronomy. Topics covered include different telescope designs and their respective merits and short comings, descriptions of the common aberrations encountered in optical systems, eyepiece designs and the trade offs in correcting different aberrations, field flattener and coma corrector design, focal reducers and extenders. A most highly recommended book with thorough explanations. An understanding of the basic principles contained here arms the reader with the necessary knowledge to make decisions about choosing equipment based on facts rather than marketing hype or unfounded emotion. This book will both arouse your curiosity and answer your questions. Why are there so many different kinds of telescopes? What does each type have to offer? What makes one telescope better than another? Which are best? Why? What are the tradeoffs? As a telescope buyer, you will be better informed; as a telescope maker, you will be able to design custom optics. Many readers will find the analyses of existing designs the most valuable part of the book. Newtonians, Cassegrains, Maksutovs, Schmidt cameras and more are described and analyzed so that you can easily compare them. What's your dream telescope? This book will help you choose it. Others will make use of the power they now have to check, test, and analyze new telescope designs. The design and raytrace programs available as an option to this book will give you the tools you need to begin with a basic design and work systematically until you have created an optimized optical system that meets your personal design criteria. You'll be able to try new types of glass, design a telescope around that corrector shell you have parked in the basement, even compare the performance of many different eyepieces on your telescope. No longer must you, as an amateur astronomer, meekly accept someone else's opinion about a telescope design. You can scrutinize existing designs and improve them to meet your own standards.