BBC
Bbc: Gcse Bitesize: Lenses
Lenses are precisely shaped pieces of glass that have been developed and used in corrective glasses, telescopes, microscopes, binoculars, and magnifying glasses. They can be convex or concave. Links are provided to a video an a test.
Michigan Reach Out
Making a Water Lens
This site provides a basic experiment that shows how a lens works. This lesson plan explains nearsightedness and farsightedness. It also explains concave and convex lenses.