That would be the Keck I and II telescopes on Mauna Kea, Hawaii. Each telescope consists of 36 hexagonal mirrors, each four times bigger than the Palomar telescope mirror ( 200 inches) and the total size of the segmented mirror is 10 meters ( 400 inches). It can study galaxies with apparent magnitudes of nearly +28m and when the two telescopes operate in an interferometer mode, they have a resolving power at 2 microns wavelength of 0.005 arc seconds or 8 times better than the Hubble Space Telescope. They have been operating in research-mode since 1997.