As in the case of prisms, a clear understanding of key aspects of mirror design is necessary before we consider the various techniques available for mounting those mirrors. This chapter deals largely with the geometric configurations of different types of mirrors, their functions, and the reasons why they are designed as they are. Because mirror size is a prime driver of design and of material choice, we consider sizes ranging from small ones with diameters of a few millimeters to about 0.5 m (1.6 ft) to large, astronomical-telescope sized ones with diameters as large as about 8.4 m (27.6 ft). How the intended method of manufacture influences design is considered, as appropriate, throughout the chapter. We begin by listing the applications of mirrors, illustrating the uses of mirrors to control image orientation, and defining the relative advantages of first- and second-surface mirror types. How to approximate the minimum aperture dimensions for a tilted reflecting surface located in a collimated or noncollimated beam is considered next. We then describe various substrate configurations that might be employed to minimize mirror weight and/or self-weight deflection. Modern technology for thin facesheet adaptive mirrors is summarized briefly. Selected designs for metallic mirrors are considered. The chapter closes with a few observations about the design and use of pellicles.
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