In a standard camera lens, light is focused onto a single point in order to magnify a scene. In telescopes, on the other hand, lenses work differently, by reflecting light back and forth to achieve greater magnification. This idea can also be thought of as "folding" light.
Scientists have discoverd that, in medieval churches, stained glass windows painted with gold purify the air when heated by the sun. The researchers hope that this discovery could also be used for modern technologies, since the chemical reaction involved is very energy-efficient.