Introduction

This chapter deals with the properties of mirrors or reflecting surfaces. Two types of mirrors will be looked at: (a) plane mirrors and (b) curved mirrors. So far, we have tended to concentrate on the paraxial properties of optical systems and therefore looked at such phenomena as image formation in terms of paraxial rays, because these rays are aberration free. When we discuss the properties of plane mirrors, we need not restrict ourselves to paraxial rays because plane mirrors are aberration free and therefore we can use either paraxial or finite rays. However, when we discuss the properties of curved mirrors, these are not free of aberration and therefore we must return to paraxial optics.

Optical systems can be constructed solely of mirrors or reflecting elements and such systems are called catoptric systems. Systems that consist of refracting and reflecting elements are called catadioptric systems. In Chapter 4, we showed how to use paraxial ray tracing to study the properties and image formation in such systems. In this chapter, we will look at the properties of single mirrors and simple mirror systems, starting with plane mirrors.

Plane mirrors

In this section, we will investigate the properties of plane mirrors. These properties are useful in their own right, but are also very useful in understanding the properties of systems of plane mirrors or reflecting surfaces, such as occur in some reflecting prisms, which are discussed in Chapter 8.

The optics of plane mirrors can be analysed using Snell's law. For reflection, Snell's law reduces to the statement that the angle of reflection is equal to the angle of incidence.