ABSTRACT
A Model for the Geometry of Camera Lenses Although there are a number of models describing the behavior of light, the one used by lens designers is the simplest, namely the ray model. Before there were computers, the designing of a new lens was a complicated business involving months of laborious ray tracing. Today, designers can optimize a lens design in a few minutes using an off-the-shelf computer program. The variables to juggle are the refractive indices of the components; the color dispersions of the glasses; the number of components and their curvature, thickness, and separation; and the position of the stop. This all represented a heavy meal for the old-time designer equipped with only a slide-rule and a set of tables of glass types. But to a modern computer they signify no more than a light breakfast. The result still doesn’t predict everything about the performance of the final lens; this demands a more sophisticated model, as we will see in Chapter 6. However, a simple ray model is sufficient to describe how a lens forms an image, and to explain why it is necessary to have more than one element in a camera lens. To begin with we will look at the properties of a simple convex lens.
