
2
BASIC GEOMETRIC OPTICS
The concepts of geometric optics were well understood long before the wave nature of light
was fully appreciated. Although a scientic basis was lacking, reection and refraction were
understood by at least the 1600s. Nevertheless, we will follow the modern approach of basing
geometric optics on the underlying wave theory. We will begin by deriving Snell’s law from
Fermat’s principle in Section 2.1. From there, we will develop equations to characterize the
images produced by mirrors (Section 2.3) and refractive interfaces (Section 2.4). Combining
two refractive surfaces, we will develop equations for lenses in Section 2.5,