James Clerk Maxwell telescope. View of the primary and secondary mirrors of the James Clerk Maxwell Telescope (JCMT). JCMT is a 15 metre telescope designed for observations at millimetre and sub- millimetre wavelengths (between radio & infrared). The primary or main mirror, paraboloid in shape, is composed of 276 adjustable panels. Radiation is focused from this mirror onto a small secondary hyperboloid mirror held above the main mirror by a metal frame. Infrared detectors then receive the signal from a cabin located below the main mirror. The telescope is seen housed in its observatory. JCMT is located at 4200 metres altitude on the summit of the dormant volcano Mauna Kea in Hawaii.