Largest primary mirror (non-segmented)

The largest observatory mirrors are those in the dual-tube Large Binocular Telescope, but the largest single primary mirror forms part of Japan’s Subaru Telescope on Mauna Kea, Hawaii, USA. The 8.2-m-wide (26-ft 10-in) mirror is made from 20‑cm-thick (8‑in) glass weighing 22.8 tonnes (50,265 lb). With the help of 261 actuators to constantly keep the mirror focused, warping is limited to less than 0.1 microns (0.00001 millimetres). The largest reflector telescope in our 1955 edition was the Hale Telescope of the California Institute of Technology on Palomar Mountain, USA, with its 5.1-m-wide unsegmented mirror. The record today is now categorized as the Largest primary mirror (non-segmented).

The largest land-based telescope in absolute terms is the segmented Gran Telescopio Canarias, at 10.4 m wide.