The twin Keck telescopes are the largest optical telescopes in the world, each with a diameter of 10 meters.  They are located on the summit of an extinct volcano (Mauna Kea) on the Big Island of Hawaii.  These mirrors collect optical and infrared light with wavelengths from 3000 Angstroms to 5 microns.   For more information, visit http://www.keckobservatory.org.