The rebirth of the MMT

At the time of its dedication in 1979, the 4.5-m Multiple Mirror Telescope was the third largest optical telescope in the world. It featured ambitious design innovations including lightweight, multiple primary mirrors, a corotating building and an altitude-azimuth mount. The successful completion of the MMT heralded the beginning of the current generation of telescope design. The telescope was decommissioned in March 1998 and is being replaced with a 6.5-m, single-primary telescope, which will see first light in mid-1999. The new telescope will be the first to use a very large spin-cast borosilicate primary mirror produced in the Steward Observatory Mirror Lab. The conversion of the MMT will provide: (1) an increase of more than a factor of two in light gathering power, (2) a factor of 15 increase in the diameter of the field of view and (3) a two-reflection adaptive focus for diffraction-limited imaging at wavelengths longer than 1 μm