ABSTRACT
These are intrinsic faults of lenses whose surfaces are portions of spheres, and they can all be constructed geometrically by drawing rays following Snell’s law of refraction, which says that when a light ray moves from one medium to another it will change direction according to the formula
sin i/sin r = n
where i and r are the angles made by the light rays to a line normal to the surface and n is the refractive index (Figure 7.1).
