This is a basic tutorial on simple lenses suitable for non-physics majors.  It explains how lenses are classified according to their curvature and the type of refraction that occurs when light travels through them.

This item is an advanced tutorial for students of introductory optics on simple lenses and the geometry involved in tracing light rays through lenses.  It explores lens structure, convergence and divergence, optical distortion, and contains links to 15 related Java simulations.