Modern reflecting telescopes have mirrors up to 355 inches (8.4 meters) in diameter. A number of telescopes have one primary mirror of approximately that size. Examples include the Subaru Telescope and Gemini North telescopes on Mauna Kea, 240 Hawaii, and the Gemini South telescope on Cerro Pachon, Chile.

The largest telescopes, though, combine smaller mirrors together, using them to create an optical system that is equivalent to a telescope with a single large mirror. The Keck 1 and Keck 2 Telescopes on Mauna Kea, Hawaii, each have thirty-six hexagonal mirrors that fit together to create the equivalent of a telescope 394 inches (10 meters) in diameter. The Gran Telescopio Canarias on the Spanish island of La Palma also has thirty-six mirrors, combining to create a 410-inch (10.4 meter) telescope. The Large Binocular Telescope on Mount Graham, Arizona, has two eight-meter mirrors on a single mount, creating the equivalent of a single telescope 440 inches (11.2 meters) across. The Very Large Telescope on Cerro Paranal, Chile, is actually four separate telescopes, each eight meters across, positioned side-by-side on the same mountain peak. They are designed to work separately, and eventually astronomers hope to have them work together as a single telescope with an equivalent diameter of 630 inches (16 meters) across.