Cardinal Points

We have learned about the formation of image by a single lens. Now, we want generalization of image formation by a complex optical system having a number of lenses and mirrors. In general, we have a number of refracting surfaces 1, 2, 3, ..., m in sequence, each one of which forms image under well-defined laws of refraction. To find final image of an object after refractions through these surfaces, we have to apply m relations. Doing so is tedious and complex job. It is however possible to deal with m refractions together if we define some points, called the cardinal points. These cardinal points enable us to find final image of an object in a single step. In the present chapter, we have discussed about the cardinal points and their application for formation of image of an object.