ABSTRACT
This chapter aims to show how points in subject/object space are related to points in the image space for ideal lenses. A thin lens is a design tool, used to simulate a real lens during the preliminary stages of optical system design and analysis. The simple thin lens provides a useful model for understanding all lenses. The earliest lenses were made of polished crystals, and it was not until the Middle Ages that glass lenses were produced. By the 13th century, glass lenses were good enough to be used in spectacles for the correction of presbyopia. With the paraxial approximation, it is easy to derive equations for a simple thin lens. The subscripts on the left-hand side can be dropped because the combined set of thin lenses only has one subject distance and one image distance. The conclusion is that the focusing power of a set of lenses can be computed by adding their separate powers.
