Through a Fresnel Lens

This portrait of me was taken by Bob Hallock, the professor whose class on the physics of light I am auditing at the University of Massachusetts. I'm holding by far the largest Fresnel lens I have ever seen, which Bob used as a demo in the class. (I would have blipped Bob through the lens, but he was too modest.)

This type of lens was developed by French physicist Augustin-Jean Fresnel (pronounced freh-NELL), originally for lighthouses. It collapses what would otherwise be a thick convex lens into a thin sheet or set of thin rings. It has many uses besides lighthouses, including overhead and other sorts of projectors, reading lenses--and--not least--the "Better Beamer" used by wildlife photographers to channel their flash beam with telephoto lenses.