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Ophthalmic Optics Handbook of Ophthalmic Optics Published by Carl Zeiss, 7082 Oberkochen, Germany. Revised by Dr. Helmut Goersch ZEISS Germany All rights observed. Achrostigmat®, Axiophot®, Carl Zeiss T*®, Clarlet®, Clarlet The publication may be repro• Aphal®, Clarlet Bifokal®, Clarlet ET®, Clarlet rose®, Clarlux®, duced provided the source is Diavari ®, Distagon®, Duopal ®, Eldi ®, Elta®, Filter ET®, stated and the permission of Glaukar®, GradalHS®, Hypal®, Neofluar®, OPMI®, the copyright holder ob• Plan-Neojluar®, Polatest ®, Proxar ®, Punktal ®, PunktalSL®, tained. Super ET®, Tital®, Ultrafluar®, Umbral®, Umbramatic®, Umbra-Punktal®, Uropal®, Visulas YAG® are registered trademarks of the Carl-Zeiss-Stiftung ® Carl Zeiss CR 39 ® is a registered trademark of PPG corporation. 7082 Oberkochen Optyl ® is a registered trademark of Optyl corporation. Germany Rodavist ® is a registered trademark of Rodenstock corporation 2nd edition 1991 Visutest® is a registered trademark of Moller-Wedel corpora• tion Reproduction and type• setting: SCS Schwarz Satz & Bild digital 7022 L.-Echterdingen Printing and production: C. Maurer, Druck und Verlag 7340 Geislingen (Steige) Printed in Germany HANDBOOK OF OPHTHALMIC OPTICS: Preface 3 Preface A decade has passed since the appearance of the second edition of the "Handbook of Ophthalmic Optics"; a decade which has seen many innovations not only in the field of ophthalmic optics and instrumentation, but also in standardization and the crea• tion of new terms. This made a complete revision of the hand• book necessary. The increasing importance of the contact lens in ophthalmic optics has led to the inclusion of a new chapter on Contact Optics. The information given in this chapter provides a useful aid for the practical work of the ophthalmic optician and the ophthalmologist. The "Handbook of Ophthalmic Optics" is intended both as systematic reading material and - due to its extensive listing of optical terms - a reference work. It is not intended as, and cannot take the place of a textbook. Reference literature, a list of specialist terms and tables are contained in the newly arranged appendix. We would like to extend our gratitude to all those who have contributed to the creation of this third edition of the hand• book. Our special appreciation is due to Dr. Helmut Goersch, who also edited the German edition, Dr. Heinz Baron for the chapter on Contact Optics, and to Mr. M. Jalie, SMS A, FBDO (Hons), Hon CGIA, MBIM, Head of Department of Applied Optics, City and East London College, London, England, with• out whose kind and indefatigable assistance the English edition would not have been possible at all. Carl Zeiss Oberkochen 4 HANDBOOK OF OPHTHALMIC OPTICS: Contents Physical Optics See also page 8 Geometrical optics Components of ray tracing. Reflection of light. Refraction of light. Lenses. Optical image formation with lenses and lens systems. Aberrations. Wave optics Electromagnetic radiation. Interference and diffraction. Polarisation. Light technology Photometry. Material properties.Light sources. Light guides. Physiological Optics See also page 58 The eye Structure of eye. Accommodation. The pupil. Visual performance. Colour vision. Emmetropic eye. Ametropic eye. Monocular correction of eye. Binocular vision Fusion and vergence. Binocular space perception. Phoria and tropia. Anisometropia and aniseikonia. Binocular correction of eye. Spectacle Optics See also page 100 Spectacle lenses Terminology. Single-vision lenses with spherical power. Single-vision lenses with astigmatic power. Single-vision lenses with prismatic power. Bifocal, multifocal and progressive lenses. Special types of spectacle lenses. Lens power determination. Image-forming properties. Light-transmission properties. The lens/eye system Terminology. Monocular centration. Binocular centration. Accommodative effort and amplitude of accommodation. Space perception. Low vision aids. HANDBOOK OF OPHTHALMIC OPTICS: Contents 5 Contact Optics See also page 156 Contact lenses Terminology. Contact lenses with spherical power. Contact lenses with astigmatic power. Bifocal and multifocal contact lenses. Image-forming properties. Light-transmission properties. Contact lens/eye system Terminology. Hard contact lenses and spherical ametropia. Hard contact lenses and astigmatic ametropia. Soft contact lenses. Optical differences from spectacle lens correction. Reasons for use. Instrument Optics See also page 188 Optical instruments Lupes. Microscopes. Telescopes. Photographic lenses. Projection lenses. Endoscopes. Geodetic instruments. Ophthalmic and Focimeters. Instruments for objective vision testing. ophthalmological instruments Instruments for subjective vision testing. Equipment for lens fitting. Equipment for contact lens fitting. Other instruments. Materials See also page 246 Glass Composition and properties. Shaping process. Strengthening techniques. Plastics Composition and classification. Plastics for spectacle lenses. Plastics for contact lenses. Plastics for spectacle frames. Metals and other materials Noble metals. Alloys for spectacle frames. Other materials. Appendix Tables page 277 Specialist terms page 333 Bibliography page 338 Index page 340 PHYSICAL OPTICS 8 PHYSICAL OPTICS Geometrical Optics Components of ray tracing Light ray 11 Bundles and pencils 1 1 Angles, distances and points 11 Optical image formation 12 Reflection of light Law of reflection 12 Total reflection 13 Mirrors 13 Refraction of light Refractive index 15 Law of refraction 15 Dispersion 15 Plane parallel plates 17 Prisms 17 Lenses Lenses with spherical power 20 Surface power 20 Equivalent power and focal length 21 Vertex power and vertex focal length 22 Principal points 23 Lenses with astigmatic power 24 Optical image formation with Optical systems 26 lenses and lens systems Determination of the image 26 Real image formation 30 Virtual image formation 30 Newton's formula 30 Astigmatic image formation 31 Stops 31 Aberrations Requirements on image formation 33 Spherical aberration 33 Coma 33 Astigmatism of oblique incidence 34 Field curvature 34 Distortion 34 Chromatic aberration 35 Corrected optical systems 36 PHYSICAL OPTICS 9 Wave Optics Electromagnetic radiation Light 37 Velocity of light 38 Interference and diffraction Interference 38 Newton's rings 39 Reduction of reflections 39 Interference filters 40 Diffraction 40 Holography 41 Polarisation Brewster's law 41 Bi-refringence 42 Dichroism 43 Optical activity 43 Light Technology Photometry Terminology 44 Luminous efficacy 46 Material properties Terminology 46 Influence of light path 4S Light sources Daylight 49 Incandescent lamps 50 Fluorescent lamps 50 Spectral lamps 50 Lasers 51 Standard illuminants 51 Colour temperature ^2 Light guides Principle 52 Numerical aperture 52 Attenuation 53 Solid and liquid light guides 53 Optical fibres and fibre bundles 54 Image carriers and shape converters 54 Tapered light guides 55 Optical waveguides 55 PHYSICAL OPTICS: Geometrical Optics 11 Geometrical Optics Components of ray tracing Light ray A light ray is an imaginary mathematical line denoting the direction of propagation of light energy; single light rays do not exist in reality. The light rays are perpendicular to the wave fronts of wave optics and in geometrical optics serve to represent changes in light propagation through optical components. Bundles and pencils Light rays with a common point of intersection form a homo- centric bundle. If the rays emanate from this point of intersec• tion which lies at a finite distance, the bundle is divergent; if they run towards the point of intersection, it is convergent. The point of intersection for a parallel ray bundle lies at infinity. A pencil shows the ray path in one plane and contains the point of intersection of the rays. Angles, distances and The angles and distances used in geometrical optics to describe points a ray path are given a mathematical sign in accordance with the following rules. Angles in the anti-clockwise direction are taken to be positive, and those in a clockwise direction to be negative. The correct direction of rotation for the angles of incidence, reflection and refraction is obtained by rotating the normal towards the ray. For the angle of deviation, the direction of the incident ray is rotated towards the refracted ray. For angles between a ray and the optical axis, the ray is rotated towards the axis. Distances are taken to be positive when measured in the direc• tion of the light and negative when measured in the opposite direction; distances perpendicular to the optical axis are taken to be positive when measured upwards, and negative when they are measured downwards. The radius of curvature of an inter• face is measured as the distance from the vertex to the centre of curvature. In graphic representations the direction of light should run from left to right if possible. The parallel displacement of a ray to the right (of the direction of light) is taken to be positive, and negative when to the left. Angles are denoted by small Greek letters, distances by small Roman letters and points by capital Roman letters (Table 1). 12 PHYSICAL OPTICS: Geometrical Optics Optical image formation Optical image formation involves the creation of a related image point O' for each object point O; in the image formation process the position of the point of intersection changes for the rays of each individual bundle. The angle between two bundle rays (the vergence of the ray bundle) can be retained in optical image formation (e.g. in image formation through a
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