Contents

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Preface xiii

Chapter 1 Introduction

1.2. Approach to Subject 4

1.3. Outline of Book 4

Chapter 2 Preliminaries: Definitions and Paraxial Optics 7

2.1. Sign Conventions 8

2.2. Paraxial Equation for Refraction 9

2.3. Paraxial Equation for Reflection 12

2.4. Two-Surface Refracting Elements 14

2.5. Two-Mirror Telescopes 17

2.6. Stops and Pupils 22

2.7. Concluding Remarks 25 Bibliography 26

Chapter 3 Fermat's Principle: An Introduction 27

3.1. Fermat's Principle in General 28

3.2. Fermat's Principle and Refracting Surfaces 31

3.3. Wave Interpretation of Fermat's Principle 36

3.4. Fermat's Principle and Reflecting Surfaces 37

3.5. Conic Sections 41

3.6. Fermat's Principle and the Atmosphere 42

3.7. Concluding Remarks References Bibliography

Chapter 4 Introduction to Aberrations

4.1. Reflecting Conies and Focal Length

4.2. Spherical Aberration

4.3. Reflecting Conies and Finite Object Distance

4.4. Off-Axis Aberrations

4.5. Aberration Compensation References Bibliography

Chapter 5 Fermat's Principle and Aberrations

5.1. Application to Surface of Revolution

5.2. Evaluation of Aberration Coefficients

5.3. Ray and Wavefront Aberrations

5.4. Summary of Aberration Results, Stop

5.5. Aberrations for Displaced Stop

5.6. Aberrations for Multisurface Systems

5.7. Curvature of Field

5.8. Aberrations for Decentered Pupil

5.9. Concluding Remarks Appendix A: Comparison with Seidel References Bibliography

Chapter 6 Reflecting Telescopes

6.1. Paraboloid

6.2. Two-Mirror Telescopes

6.3. Alignment Errors in Two-Mirror Telescopes

6.4. Three-Mirror Telescopes

6.5. Four-Mirror Telescopes

6.6. Concluding Remarks References Bibliography

Chapter 7 Schmidt Telescopes and Cameras

7.1. General Schmidt Configuration

7.2. Characteristics of Aspheric Plate

7.3. Schmidt Telescope Example

7.4. Achromatic Schmidt Telescope at Surface

Theory

7.5. Solid- and Semisolid-Schmidt Cameras 181

References 184

Bibliography 184

Chapter 8 Catadioptric Telescopes and Cameras 185

8.1. Schmidt-Cassegrain Telescopes 18 5

8.2. Cameras with Meniscus Correctors 197

8.3. All-Reflecting Wide-Field Systems 204 References 205

Chapter 9 Auxiliary Optics for Telescopes 206

9.1. Field Lenses, Flatteners 207

9.2. Prime Focus Correctors 210

9.3. Cassegrain Focus Correctors 216

9.4. Cassegrain Focal Reducers 220

9.5. Atmospheric Dispersion Correctors 225

9.6. Fiber Optics 237 References 239 Bibliography 239

Chapter 10 Diffraction Theory and Aberrations 240

10.1. Huygens-Fresnel Principle 241

10.2. Perfect Image: Circular Aperture 246

10.3. The Near Perfect Image 257

10.4. Comparison: Geometric Aberrations and the Diffraction Limit 270

10.5. Diffraction Integrals and Fourier Theory 271 References 275 Bibliography 275

Chapter 11 Transfer Functions; Hubble Space Telescope 277

11.1. Transfer Functions and Image Characteristics 277

11.2. Hubble Space Telescope, Prelaunch Expectations 291

11.3. Hubble Space Telescope, Postlaunch Reality 298

11.4. Concluding Remarks 302 References 303 Bibliography 303

Chapter 12 Spectrometry: Definitions and Basic Principles 304

12.1. Introduction and Definitions 305

12.2. Slit Spectrometers 308

12.3. Fiber-Fed Spectrometers 317

12.4. Slitless Spectrometers 318

12.5. Spectrometers in Diffraction Limit 318 References 320 Bibliography 320

Chapter 13 Dispersing Elements and Systems 321

13.1. Dispersing Prism 321

13.2. Diffraction Grating; Basic Relations 323

13.3. Echelles 327

13.4. Grating Efficiency 331

13.5. Fabry-Perot Interferometer 342

13.6. Fourier Transform Spectrometer 347

13.7. Concluding Remarks 350 References 350 Bibliography 350

Chapter 14 Grating Aberrations; Concave Grating Spectrometers 352

14.1. Application of Fermat's Principle to Grating Surface 353

14.2. Grating Aberrations 357

14.3. Concave Grating Mountings 362 References 367 Bibliography 367

Chapter 15 Plane Grating Spectrometers 368

15.1. All-Reflecting Spectrometers 369

15.2. Pixel Matching 377

15.3. Fast Spectrometers 378

15.4. Fiber-Fed Spectrometers 383

15.5. Echelle Spectrometers 384

15.6. Nonobjective Slitless Spectrometers 396

15.7. Concluding Remarks 407 References 407 Bibliography 407

Chapter 16 Adaptive Optics: An Introduction 409

16.1. Effects of Atmospheric Turbulence 410

16.2. Correction of Wavefront Distortion 415

16.3. Adaptive Optics: Systems and Components 421

16.4. Concluding Remarks 423 References 424 Bibliography 424

Chapter 17 Detectors, Signal-to-Noise, and Detection Limits 425

17.1. Detector Characteristics 426

17.2. Signal-to-Noise Ratio 433

17.3. Detection Limits and Signal-to-Noise Ratio 435

17.4. Detection Limits: Stellar Photometry 438

17.5. Detection Limits: Spectroscopy 440 References 443 Bibliography 443

Chapter 18 Large Mirrors and Telescope Arrays 444

18.1. Large Mirrors 444

18.2. Telescope Arrays; Interferometers 451 References 457 Bibliography 457

Table of Symbols 459

Index 467

This Page Intentionally Left Blank

When I began thinking about and working on this second edition, it became clear early on that substantive additions to the first edition were in order. Although the optical principles upon which the earlier text was based have not changed, the ingenuity and resourcefulness of astronomers in the intervening years have led to many exciting new instrumental developments. These developments, in turn, have meant a greatly increased efficiency in gathering data from celestial sources. As one example to illustrate this change, note the use of optical fibers to feed light from a hundred or more galaxies at a time into a spectrometer, rather than the traditional one galaxy at a time approach.

Other dramatic developments within the past decade include implementing or planning for techniques of adaptive optics to compensate for the atmosphere, and the almost total adoption of solid-state detectors arrays. But the biggest change of all is only starting to become reality, that of a significant number of ground-based telescopes of near diffraction-limited quality and apertures greater than six meters in diameter. This greatly increased light gathering power will undoubtedly revolutionize observational astronomy.

In view of these developments, and in response to the many comments I received on the first edition, my thrust in this rework has been two-fold. First, many portions of the text were rewritten or amended to make the explanations more clear and to correct errors. In some cases this meant adding additional material, such as spot diagrams or wavefront maps; in other cases words and figures were removed. Second, new sections were added to many chapters and one new chapter, on adaptive optics, was added. The overall format of the first edition has not been changed, and I hope the reader will find the changes in this edition to be positive ones.

As in the first edition, my intent is to emphasize basic principles of optics and how these principles are used in the designs of specific types of instruments. The treatment is limited to telescopes and cameras that use near-normal incidence optics and spectrometers with dispersive elements or interferometers. Numerous examples of system characteristics are given to illustrate the optical performance that can be expected. An outline of the topics covered is given in Chapter 1.

The level of presentation and approach are appropriate for a graduate student in astronomy approaching the subject of astronomical optics for the first time. Although the basic principles of optics are discussed, it is assumed that the reader has the equivalent of an intermediate-level optics course at the undergraduate level. This book should also serve as a useful reference for active researchers.

Because the presentation is not simply a compilation of types of telescopes and spectrometers, the reader should consult the original sources for details on specific instruments or telescopes. I have given an expanded bibliography and list of references, including conference proceedings, to facilitate further exploration. I have also added a table of symbols and their meanings as an aid to the reader.

A number of persons contributed directly or indirectly to the writing of the first edition and this revision. First and foremost I thank Arthur Code, who gave me the opportunity of participating in the development of the Wisconsin Experiment Package of the first Orbiting Astronomical Observatory. Since that time I have been privileged to draw upon his wealth of knowledge and to teach jointly with him on one occasion a course on astronomical optics. For his contributions I am especially grateful. My thanks also to Arthur Hoag, Robert Bless, and Donald Osterbrock for their help and support over the years, and to Robert O'Dell for his encouragement to take part in NASA's Hubble Space Telescope Project.

Although many persons contributed to this rework, I mention only a few by name. Robert Lucke gave several pedagogical suggestions, especially on my discussion of distortion, that have been incorporated into the text. Derek Salmon asked some questions about misaligned telescopes and that section has been greatly expanded in this edition. The excellent book Reflecting Telescope Optics I by Raymond Wilson has been an important resource during the revision process. For their input, and the numerous other comments I have received, I am grateful.

Finally, and most importantly, I acknowledge the support, encouragement, and patience of my wife LaVern while I worked on both editions of this book.

Daniel J. Schroeder

Errata: ASTRONOMICAL OPTICS, 2nd Edition, by Daniel J. Schroeder, ISBN 0-12-629810-6, © 2000 by Academic Press

Page Location

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Correction

Replace K with K ... i = / = /? =-1000 mm ... Replace (3m2 - 2) in ADI with Delete entire line

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Reference is Code (1973)

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