Any critical review of the technology associated with geometrical optics must certainly include a discussion of optical glass. Optical glass is a material which is familiar to all optical designers; however, few designers are familiar with the manufacturing process. This article considers optical glass from a manufacturer's point of view, with the goal of pre-senting a perspective which may help the designer to better understand why all his desired properties cannot be fulfilled and what compromises must be made. Also discussed is the meaning of terms used to quantify the inhomogeneities found in optical glass.
This tutorial is concerned with system design, more particularly with the first-order design of image-forming systems. I will attempt to survey the basic concepts and methods used in this field, with the exception of radiometric considerations, which will be covered in another tutorial. Much of the material has been extracted from my background notes on the subject(1), which may be consulted, along with the other references, for further detail.
Aberrations occur in all practical image forming systems. Some aberrations are the result of balancing during design, others are intrinsic to a particular image formation system and some are introduced as the result of the fabrication of an actual system. The type and form of these aberrations can be related to the constructional parameters of the system and can be calculated by the process of ray tracing or in some cases by analytic formulae.
Several design approaches are described which feature the use of your head as a design tool. This involves thinking about the design task at hand, trying to break it into separate, easily understood subtasks, and approaching these in a creative and intelligent fashion, as only humans can do. You and your computer can become a very powerful team when this design philosophy is adopted.
A brief outline is given of the development of the more significant types of photographic objective lens that have been introduced since the invention of photography some 145 years ago. Many other forms have been tried, but because they were inferior to, or more expensive than, existing types, they were eventually abandoned. The use of the modern electronic computer has enabled designers to experiment with more complex arrangements, some of which are now regularly manufactured.
Progress in optical design has always been a function of the computational tools available to the designer. In the last half of the Twentieth Century, progress in optical design has been propelled along by vast increases in the power of computing hardware. This development has led to a complete change in the way optical design is actually done.
Thermal, or infrared imaging systems have increased in importance in recent years. This is due to several factors: The applications of IR systems have grown dynamically in importance - IR detector technology has matured substantially, to the point where many IR. detectors are available and economically producible
The design and building of mirror systems, as contrasted with refractors, is flourishing. This is particularly true in the areas of ground-based and spaceborne astronomical telescopes, spaceborne wide-field mapping and surveillance systems, and X-ray telescopes. In the case of large astronomical telescopes, the Cassegrainian 2-mirror configuration, particularly the Ritchey-Chretien form, still is dominant because of its simplicity and versatility for narrow field imaging. Innovations revolve about the areas of cost reduction through the minimization of overall size in the midst of increasing the collecting aperture. In the case of spaceborne applications, all-reflective systems become even more necessary due to the requirements of broader spectral regions and wavelengths for which no suitable transmitting materials are available. Wide-field configurations are increasingly in demand in order to increase the information rate in mapping and surveillance applications. To this is added the spaceborne explorations in the far-UV and X-ray regions with grazing incidence reflective configurations. In all of these pursuits, the designs are seen to originate in the works of Newton, Schwarzschild, and Schmidt.
Basic aspects of visual perception are reviewed with respect to their influence on the design of optical systems whose ultimate receptor is the human eye. General characteristics and design techniques are described for coherently and incoherently coupled visual systems, using simple examples for illustration.
The word trade-off, though in common usage in most engineering fields today, is fairly new in the American language. At least it does not appear in my 1964 dictionary, but it does appear in my 1977 dictionary. It is surmised, therefore, that it must have its origins in either high technology or international diplomacy. In either event, we find that it fits what we've been doing in optical system design for many years. What do we mean by trade-off? It is a balancing of factors or conditions all of which are not attainable at the same time.
During the past 15 years, the importance of stray light control and its evaluation as an integral part of the design process for imaging systems has emerged. There has been substantial progress in the development of both analytical tools and experimental facilities. The problem has become easier and more difficult depending on the scenario. Some scenarios such as detecting point objects within a small field of view have made the problem easier as the background stray light is proportional to the field of view. Extended objects and large fields of view make the problem more difficult as does near field thermal sources. It is for these reasons that a review is in order-to assess our present technology and suggest how we might develop that technology.
The relationships between the characteristics of a source of radiation and its final energy distribution (or image) are presented. The black-body, the inverse square law, the irradiance or illumination produced on a surface, Lambert's law, the radiance or brightness of an image, and the relationship between radiometry and photometry are discussed.
This paper is concerned with the selection of optical glass in the design of imaging systems that are intended for the visible waveband. While the requirements clearly differ from one case to another, there are some general principles which are discussed in this paper. In addition, several common types of lens system are discussed in detail, and some practical examples are given.
A series of six lenses are toleranced for decentering and air spacing. Each design is characterized as requiring commercial, precision, or extra precision mounting. The advantages of edge mounting and cell mounting are compared.
The basis for, and the specific steps involved in, the determination of a suitable tolerance budget are discussed, using an R.S.S. (square Root of the Sum of the Squares) statistical addition of the tolerance effects. A numerical example is given.
In this paper we review the geometrical characteristics of optical components such as plane-parallel plates, flat mirrors, and prisms that serve extremely useful purposes in optical instruments, but nominally do not contribute optical power and, hence, cannot form images by themselves. The principal uses of such components as windows; filters; reticles; beam-folding optics; beamsplitters/combiners; image erectors, rotators and scanners; etc. are addressed. Representative configurations for these components and typical designs for mounting them into common types of instruments also are described.
The modern zoom lens for 35 millimeter photography has a focal length range extending from the wide angle to telephoto, potentially replacing several single focal length lenses or zoom lenses of small range as the standard photographic objective. This recent development appears to be the result of a continuous design evolution; each new design widening the range of power change utilized by the particular configuration. When a particular configuration is extended too far, the lens design necessary for aberration correction becomes complex, and a new configuration is developed.
Holographic Optical Elements (HOEs) are being currently used in an increasing number of applications as components of optical systems, although their use is still relatively rare. HOEs are invaluable for selected optical system applications, inappropriate for most, and potentially useful for others. The most successful applications use one or more of the HOEs' unique attributes to obtain optical system performance not possible with conventional optical elements alone. The purpose of this paper is to summarize the basic concepts involved in the use of HOEs in optical systems, to present several system examples illustrating successful applications of HOEs, and to highlight HOE attributes which are crucial to overall optical system performance.
Geometrical optics can be applied to many other areas of physics. In this paper, a few examples are chosen to illustrate how the ray tracing methods of gradient-index optics can be used for describing the propagation of ocean waves in the deep ocean, the propagation of seismic waves, the paths of sound waves, and the mirage problem. In addition, a short description of the current state of gradient-index optics and the difference between axial and radial gradients is given.