Giant Fresnel Lens

I found a company that sells giant fresnel lenses. What is a Fresnel lens? Think of a lighthouse or the top of an overhead projector. As light goes through the lens, spiral cut ridges focus the light to a focal point. You end up with the equivalent of a giant magnifying glass or parabolic mirror. There is some really juicy math invovled in calculating how to create a lens, determining the focal length and lens strength.

I framed the lens with some 2“x2“ lumber and secured it with electrical tape. When I carried the lens out of the garage, I knew we were in for a good show. The asphalt driveway started smoking. Our first target was a penny which the lens quickly melted into slag. Next up was a hamburger. We widened the focus and it flash cooked the top of the burger.


What I learned:

  1. You really need welding goggles. I have none so we had to use a spotter from a distance to help us focus. If you knelt down and tried to focus it without eye protection, you would surely suffer eye damage.
  2. If the sun is directly overhead, the lens is easier to focus and burns significantly hotter.
  3. Burgers cooked with a giant death ray don't taste very good. It's about like cooking in a microwave: you don't get the smoky taste that a BBQ gives you.