ABSTRACT
This chapter starts with a few basic rules of optics and show how they work in simple lenses. Of course, science is not just a list of independent rules, and it should be recognized that these rules can be derived from more general laws of physics. The rules are not only consistent with Maxwell's electromagnetic theory, but they can be derived from the quantum theory of photons and electrons. The refractive index depends on the frequency of the light and conditions such as the temperature and pressure that affect the properties of the material. Refractive indices have been measured for all the materials of interest in optics and can be found in tables. The ray through the center of the lens has the shortest path in air but is delayed by passage through the thickest part of lens and so on, and the lens is designed so that optical path lengths and times for all of rays shown are identical.
