UC San Diego engineers have devised an ultra-thin digital camera by folding up the telephoto lens into a slim component. The design, based on that of Cassegrain telescopes, bends and focuses light back and forth inside a 5 millimeter optical crystal. The result is a thin digital camera that can zoom in and take telephoto shots. Today’s cell phone cameras may get the job done for wide angle shots, but zooming them in often creates images of poor quality. This technology could improve the photo-taking experience for cell phones.