American Science & Surplus: Optics – Lenses and Lens Cleaners:
The Mother Of All Fresnel Lenses
It came from either outer space, or a projection TV. Our largest Fresnel lens measures 49-1/8″ x 37-1/8″ x 1/16″ thick, with a 42″ focal length. Build your own lighthouse or projection TV, teach optical properties to students, or just turn your 21-inch model into one with a tavern-size picture. Held in the sun, the lens will concentrate rays enough to cook eggs or torch lumber. And, under adult supervision in the parking lot, employees of a certain un-named scientific and surplus purveyor actually melted pennies in seconds. Extremely cool and done strictly, we assure you, to determine the lens’s focal length. Do not, we shouldn’t have to remind you, store this puppy in direct sunlight. Or let the underage or under-mature sneak it into the sunlight.
Couple this with a solar heating system or a Stirling engine (who knows how little sunlight it could make use of?). Melting pennies in seconds? Yikes! Even an old-fashioned steam engine could be run off something like this: the inefficiency of it isn’t such a big deal when the cost of your main input is zero.