Georgia State University
Georgia State University: Hyper Physics: Dispersion
The phenomenon of light dispersion is explained with a formula and a practice form for calculating Abbe's number.
Science Struck
Science Struck: How Do Optical Illusions Work?
Learn how the eyes play tricks on us when we look at optical illusions. This resource explains many of the techniques used to challenge our visual perception.
University of Chicago
University of Chicago: Reflector and Refractor
From the Yerkes Observatory Virtual Tour web site. Compares and contrasts reflecting and refracting telescopes. A link from the page leads to a second page which explains why most modern research telescopes are reflecting telescopes.