This resource is the full index of materials by the same authors on the topic of Light and Color.  It includes introductory tutorials on lenses, electromagnetic radiation, refraction, reflection, diffraction, polarization of light, light filtration, and properties of light.  This page also links to more than 25 related interactive Java simulations within the broad category of Light.

This item is a full tutorial for introductory optics on the topic of lenses.  It explains how lenses are classified based upon their refractive properties, and contains multiple drawings of various lens types within a focal plane.