Big Optics interactive, Science Museum, London, 1992.
© Science Museum / Science & Society Picture Library
The giant lens in the Big Optics exhibit can be used as a magnifying glas. Unlike a normal lens which is curved, it is made from a flat sheet of plastic. This has tiny steps in it to bend the light as it comes through. This sort of lens is used in car headlights to make the beam of light spread in the right direction.