Applied Photographic Optics

Sidney Ray

• Publisher: Routledge
• Year: 2002
• ISBN:
  9781136097010
• Edition: 3
• Topic: Media & Performing Arts
• Subtopic: Digital Media

Selected by the American Library Association's 'Choice' magazine as "best technical book", the first edition of this book soon established itself as the standard reference work on all aspects of photographic lenses and associated optical systems. This is unsurprising, as Sidney Ray provides a complete, comprehensive reference source for anyone wanting information on photographic lenses, from the student to the practitioner or specialist working with visual and digital media worldwide. This third edition has been fully revised and expanded to include the rapid progress in the last decade in optical technology and advances in relevant electronic and digital forms of imaging. Every chapter has been revised and expanded using new figures and photographs as appropriate, as well as extended bibliographies. New chapters include details of filters, measurements from images and the optical systems of digital cameras. Details of electronic and digital imaging have been integrated throughout. More information is given on topics such as aspherics, diffractive optics, ED glasses, image stabilization, optical technology, video projection and new types of lenses.A selection of the contents includes chapters on: optical theory, aberrations, auto focus, lens testing, depth of field, development of photographic lenses, general properties of lenses, wide-angle lenses, telephoto lenses, video lenses, viewfinder systems, camera movements, projection systems and 3-D systems.

1 Introduction

The efficient and effective use of visual media such as photography, film, video and digital imaging is enhanced by an understanding and working knowledge of the optical principles involved in visual perception, image formation and subsequent recording processes for access, duplication and dissemination of images. These principles find application at every stage, from viewing and lighting the subject to the choice and use of suitable optical equipment and the evaluation of the final image.

The topic of photographic optics is taken to cover not only lenses but also viewfinder systems, focusing arrangements and the numerous ancillary optical systems found not only in cameras but also to varying extents in associated apparatus for the projection and viewing of images. The topic also now includes optical aspects of electronic and digital imaging using electro-optical and opto-electronic systems that have replaced or enhanced traditional optical and mechanical arrangements. This electronic enrichment of equipment extends both their imaging and functional capabilities.

This book is intended primarily for the student, general practitioner or specialist actively working with visual, digital and electronic media, and much less so for the optical designer or engineer. Its primary objectives are to give a selective overview and explanation of relevant optical theory and technology, to explain the capabilities and limitations of contemporary lenses and optical systems, and finally, to demonstrate the integration of both theory and optical systems into a range of imaging applications and craft skills. To develop this approach, the contents are divided into three major sections that detail optical theory, lens properties and optical systems.

The design of lenses and optical systems is a specialist subject and has been excluded; this is deliberate, as excellent texts are available elsewhere, but numerous formulae, data and examples have been included to permit calculation of the first-order and more general properties of lenses and the layout of optical systems. To this end, both the simplified notation and the sign convention used give most formulae in their traditional form so as to relate to other frequently used texts. Any necessary departures from these are clearly indicated to avoid possible ambiguities.

Where appropriate and useful, proofs or derivations are provided of various important relationships and formulae, especially if these are not readily accessible elsewhere. Only a modest knowledge of science and mathematics is necessary to obtain useful insights from the text. Various practical situations are described to provide numerical examples and explanations.

The historical development of photographic optics is not covered in depth, only the significant developments of the nineteenth century are discussed and their later optimized realization in contemporary designs. However, some topics require some evolutionary background to be explained. Regrettably, the very large number of individual lens designs now available excludes the possibility of a contemporary directory of lens types and makes, but designs of technological importance are detailed where possible.

The comprehensive lists of both references and further reading provide details of primary source material and much fuller mathematical or theoretical treatments, together with case histories and extensive notes on usage. Tables of data, graphs and specific details of practical situations are given in the hope that these may make this book a useful companion rather than just a reference volume.

This third edition has been revised and enlarged to cover the numerous advances in most topics in the last decade, particularly in optical technology, as well as photographic, video, electronic and digital imaging systems. Where possible, new material has been integrated with the original text to keep intact the original structure of the book but inevitably some rearrangement of material has been necessary. The only significant removal has been a chapter on holography, but this has been replaced by material on the optics of digital cameras. To reflect the increasing use of digital photography, relevant material has been integrated throughout the chapters. The number of relevant references and suggestions for additional reading has been increased significantly and numerous new diagrams and illustrations are provided. A number of plates have been used to complement the text and diagrams. The opportunity has been taken to correct any errors and omissions in the previous edition. The level and objectives of the contents have not been changed, and by detailing contemporary equipment and practices this book should remain useful for both study and reference purposes.

2 The role of the lens in photography

2.1 Imaging

The lens-based media of photography, cinematography, video and digital imaging in all their aspects make use of various radiation-sensitive systems in general and light-sensitive emulsions, surfaces, materials or photodetector arrays in particular.

The lens of a camera (including a motion picture camera, video camera, or electronic and digital imaging systems) is the ‘front end’ of the system in that it acts as an interface between the scene or subject and the viewing or recording system. The prime function of the lens is to form a sharp optical image on the surface of the recording medium or display system. The image must have sufficient detail or resolution for the situation, and an adequate illuminance to permit a convenient exposure duration by the shutter or scanning system used. Some recording systems may dispense with imaging lenses as such, e.g. those used for holography, or assemble an image composed of pixels (picture elements) by sequential scanning of the subject or optical image as in thermography and video respectively, but associated optical components are usually needed.

Viewfinder systems permit an image to be seen in real time for subject location, focusing and composition.

2.2 Recording

There are many ways of recording a subject, from a pencil drawing to storage in various digital formats on tape or disc. Of these, photography using a lens and film can still be one of the most cost-effective and convenient, and is potentially capable of having a very high information content.

A highly corrected lens can give an image of the subject full of detail down to the natural limits set by the physical nature of light. A photographic record can be obtained from a brief exposure to this image followed by development, and may then be examined and evaluated at leisure. No other system seems to offer such a combination of convenience, sensitivity, unbiased recording, wealth of detail and image permanence for a factual representation of a complex scene.

An electronic or digital imaging system offers in addition near-immediate access (real time) to a stored image that may be recorded in analogue or digital form for archiving purposes. Post-recording image management processes include editing, manipulation, enhancement, extraction and analysis of data, principally by techniques of digital image processing.

In many instances, the most useful features of both photographic and digital systems are combined to form hybrid systems with enhanced practical convenience.

2.3 Measurement

The convenience and advantages of photographic and digital images mean that they can be used to obtain temporal and spatial data concerning or related to the subject from suitable measurements of an image or sequence of images. For fidelity and accuracy of results, any lens used in this way as a measurement tool must give an image free of any distortions, and must be capable of resolving the finest necessary detail in the subject.

2.4 Extension of visual perception

The human visual system has definite limitations to its perception in terms of spatial and temporal resolution as well as in its frequency bandwidth. Other familiar limitations include the field of view, closest focusing distance, and the lack of retention of retinal images in permanent form with complete fidelity.

Photographic and digital imaging offer significant extensions to this limited perception by the use of suitably sensitized materials and detectors, together with special-purpose lenses designed to work, for example, either in particular spectral bands, or with maximum resolution, or with extreme angles of view, or by giving magnified images of a subject inaccessible other than by optical means. Temporal behaviour may be recorded by optical dissection of a scene or by visual integration of successive optical images.

2.5 Self-expression

Photography and digital imaging are leisure activities and a means of artistic self-expression to many who lack more conventional skills of draughtmanship or artistry. The camera gives a means of presenting images in a highly subjective manner.

Furthermore, prior to the use of digital image processing routines, the subject can be manipulated optically in novel ways by the choice of viewpoint, the particular imaging properties of the lens used and by various means of distorting the final image after recording. Optical manipulation offers a variety of possibilities and the resultant image can often be inspected and approved before recording.

Lenses also offer a means of isolating, juxtaposing or combining subjects and suggesting spatial and tonal relationships of aesthetic interest, giving an artistic extension to vision in addition to the more technical purpose of recording. Habitual use of particular lenses, viewpoints or manipulated imagery may even give a recognizable style to the photography of individual practitioners.

Further reading

Burgin, V. (ed.) (1982) Thinking Photography, The Macmillan Press, London

Clark, G. (1997) The Photograph, Oxford University Press, Oxford

Darius, J. (1984) Beyond Vision, Oxford University Press, Oxford

Sontag, S. (1979) On Photography, Penguin Books, Harmondsworth

Stroebel, L., Todd, H. and Zakia, R. (1980) Visual Concepts for Photographers, Focal Press, London

Webster, F. (1980) The New Photography, John Calder, London

Williams, J. (1989) Image Clarity, Focal Press, Boston

Zakia, R. (1997) Perception and Imaging, Focal Press, Boston

3 Optical requirements

Photographic lenses and associated optics are commonplace examples of very advanced technology. In common with users of other types of optical equipment, the photographer or ‘image manager’ requests from the designer and manufacturer lenses which will satisfy stringent demands, some of which are not realizable in a single design. After analysis, however, a number of valid optical requirements may be identified for photography which may differ from those of other optical systems, e.g. as for astronomy.

A significant difference in optical terms is the unusually large acceptance angle of a photographic lens, usually called the field of view (FOV) or angle of view, as compared with, say, telescopes, microscopes or spectroscopes. For example, a ‘standard’ lens for a given format may have a field angle of some 53°, but there are legitimate demands for angles up to 220° and as little as 1° or less, or for a variable angle as given by a zoom lens.

The image plane or focal plane of a lens must normally approximate closely to a plane orthogonal to the optical axis. This minimization of curvature of field requires some balancing of the anastigmatic corrections. For some applications, devices such as an optically flat plate, reseau plate or vacuum platen may be used to ensure coincidence of image surface and planar recording medium.

Ideally, the image illumination should be independent of field angle at any point in the image plane, or not less than 70 per cent of its axial value, to contend with the contrast and exposure latitude of the recording medium. Complex optical means have been devised to approximate to this requirement, particularly so in wide-angle lenses.

The ‘drawing’ of the lens should be orthoscopic in that the image should not display curvilinear distortion of the pincushion or barrel variety, especially for applications such as architectural photography and photogrammetry. Such distortion correction is difficult to achieve in designs with significant asymmetrical optical configurations.

A lens should normally have as large an aperture as possible to provide a bright image to facilitate viewing, focusing and picture taking, especially in low levels of ambient lighting. Unlike other optical systems, which may be diffraction-limited with high resolvin...