Preface to the Second Edition

Inasmuch as the first edition of this book could be regarded as an extension and modernization of Professor Alexander Eugen Conrady’s Applied Optics and Optical Design, this second edition can be viewed as a further extension and modernization of Conrady’s 80-year-old treatise.1 As was stated in the preface to the first edition, referring to Conrady’s book, “This was the first practical text to be written in English for serious students of lens design, and it received a worldwide welcome.” Until then, optical design was generally in a disorganized state and design procedures were often considered rather mysterious by many.

In 1917, the Department of Technical Optics at the Imperial College of Science and Technology in London was founded. Conrady was invited to the principal teaching position as a result of his two decades of success in designing new types of telescopic, microscopic, and photographic lens systems, and for his work during WWI in designing most of the new forms of submarine periscopes and some other military instruments. Arguably, his greatest achievement was to establish systematic and instructive methods for teaching practical optical design techniques to students and practitioners alike. Without question, Conrady is the father of practical lens design.2,3

Rudolf Kingslake (1903–2003) earned an MSc. degree under Professor Conrady, earning himself a commendable reputation while a student and during his early career. Soon after The Institute of Optics was founded in 1929 at the University of Rochester in New York, Kingslake was appointed an Assistant Professor of Geometrical Optics and Optical Design. His contributions to the fields of lens design and optical engineering are legendary. Most lens designers can trace the roots of their education back to Kingslake. Following in Conrady’s footsteps, Kingslake is certainly the father of lens design in the United States.

1A. E. Conrady, Applied Optics and Optical Design, Part I, Oxford Univ. Press, London (1929); also Dover, New York (1957); Part II, Dover, New York (1960).

2R. Kingslake and H. G. Kingslake, “Alexander Eugen Conrady, 1866–1944,” Applied Optics, 5(1):176–178 (1966).

3Conrady commented that he limited the content of his book to what the great English electrical engineer Silvamus P. Thomson called “real optics” and excluded purely mathematical acrobatics, which Thomson called “examination optics” (see Ref. 1).

Kingslake published numerous technical papers, was awarded an array of patents, wrote a variety of books, and taught classes in lens design for nearly half a century.4 Collectively these have had a major impact on practicing lens designers and optical engineers. Perhaps his most important contribution was the first edition of Lens Design Fundamentals in 1978, followed in 1983 by Optical System Design. In the years since the first edition was published, spectacular advances in optical technology have occurred.

The pervasive infusion of optics into seemingly all areas of our lives, perhaps only dreams in 1978, has resulted in significant developments in optical theory, software, and manufacturing technology. As a consequence, a revised and expanded edition has been produced primarily to address the needs of the lens design beginner, just as was the first edition. Nevertheless, those practitioners desiring to obtain an orderly background in the subject should find this second edition an appropriate book to study because it contains about 50 percent more pages and figures than the first edition by Kingslake.

Revising this book without the participation of its first author presented somewhat of a challenge. The issues of what to retain, change, add, and so on, were given significant consideration. Having taught a number of classes in lens design and optical engineering myself during the past 35 years, often using Lens Design Fundamentals as the textbook, the importance of the student mastering the fundamental elements of practical lens design, rather than simply relying on a lens design program, cannot be overemphasized.

Notation and sign conventions used in lens design have varied over the years, but currently almost everyone is using a right-handed Cartesian coordinate system. In preparing this edition, figures, tables, and equations were changed from a left-handed Cartesian coordinate system with the reversed slope angles used by Conrady and Kingslake into a right-handed Cartesian coordinate system. The student may wonder why different coordinate systems have been used over the years. Minimization of manual computation effort is the answer. Elimination of as many minus signs as possible was the objective to both increase computational speed and reduce errors. Today, manual ray tracing is rarely done, so it makes good sense to use a right-handed Cartesian coordinate system, which also makes interfacing with other modeling, CAD, and manufacturing programs easier.

Since the first edition, a number of books have been published on the topic of aberration theory. Some authors of these books tend to suggest that wavefront aberrations are preferable to longitudinal or transverse ray aberrations. In reality, these aberration forms are directly related (see Chapter 4). The approach used by Conrady and Kingslake to study aberrations was to use real ray errors,

4A selected bibliography of the writings of Rudolf Kingslake is provided in the Appendix of this book.

optical path differences (OPD), and (D d) for chromatic correction, in contrast to wavefront aberrations expressed by a polynomial or Zernike expansion. In this second edition, the same approach is continued for various reasons, but primarily because experience has shown that beginning lens design students more intuitively comprehend ray aberrations.

The content here has been revised and expanded to reflect the general changes that have occurred since the first edition. Chapter titles remain the same except that a new overview chapter about aberrations has been added. All the chapters have been revised to some extent, often including new examples, significantly more literature references, and additional subject content. The final chapter, discussing automatic lens design, was completely rewritten. Although the types of optical systems had been limited to rotationally symmetric systems, the chapter on mirrors and catadioptric systems was expanded to include a variety of newer systems with some having eccentric pupils. Some material from Optical System Design has been incorporated without attribution. The reader will notice that trigonometric ray tracing is still discussed in this edition. The reason is that many concepts are profitably discussed using ray trace information. These discussions and examples contain the ray trace data for students to consider without having to generate it themselves.

The lack of explanations about how to use any particular computer-based lens design program was intentional because such a program is not required to learn the fundamentals; however, the student will find significant benefit in exploring many of the examples using a lens design program to replicate what is shown and perhaps to improve on or change the design. Much can be learned from such experimentation by the student. Following the philosophy of Conrady and Kingslake, this book contains essentially no problems for the student to work since there are numerous fully worked examples of the principles for students to follow and expand on themselves. Instructors can develop their own problems to supplement their teaching style, computational resources, and course objectives.

Lens design is based not only on scientific principles, but also on the talent of the designer. Shannon appropriately titled his book The Art and Science of Optical Design.5 A new feature in this edition is the occasional insertion of a Designer Note; these provide the student with additional relevant information that is somewhat out of the flow of the basic text. Reasonable effort has been given to making this edition have improved clarity and to being more comprehensive.

Although many new technologies have become available for lens designers to employ, such as diffractive surfaces, free-form surfaces, systems without

5Robert R. Shannon, The Art and Science of Optical Design, Cambridge University Press, Cambridge (1997).

symmetry, holographic lenses, polarization, Fresnel surfaces, gradient index lenses, birefringent materials, superconic surfaces, Zernike surfaces, and so on, they intentionally have not been included. Once students and self-taught practitioners have mastered the fundamentals taught in this edition, they should be able to quickly develop the ability to use these other technologies, surfaces, and materials through study of the literature and/or the manual for the lens design program of their choice.

Acknowledgments

In 1968, it was my good fortune to meet Professor Kingslake when he gave a series of lectures on lens design at Texas Instruments and, with his encouragement, I soon went to The Institute of Optics for graduate studies. Not only was he my teacher, but he also became a good friend and mentor for decades. Without question, his teaching style and willingness to share his extraordinary knowledge positively impacted my career in optical design as it did for the multitude of others who had the occasion to study under Kingslake. I am humbled and appreciative to have had the opportunity to prepare this second edition of his book and hope that he would have approved of my revisions.

My sincere gratitude is given to Dr. Jean Michel Taguenang and Mr. Allen Mann whose careful reading of, and comments about, the manuscript resulted in a better book; to Professor Brian Thompson and Mr. Martin Scott for providing access to early documents containing Kingslake’s work; and to Thompson for writing “A Special Tribute to Rudolf Kingslake.” I acknowledge, with thanks, Professor Jose Sasian, who suggested that I undertake the project of preparing this second edition, and Dr. William Swantner for many constructive discussions on practical optical design. The tireless efforts and professionalism of Marilyn E. Rash, an Elsevier Inc. Project Manager, during the editing, proofreading, and production stages of this book are sincerely appreciated.

R. Barry Johnson

Huntsville, Alabama