Nasmyth telescope

A Nasmyth telescope is a type of reflector telescope that has a secondary mirror reflecting straight back toward the primary and a flat tertiary mirror reflecting the light at a right angle before it reaches the primary. This is useful for handling heavy or bulky instruments, and some major telescopes can be configured in this manner, including:

• Keck Observatory
• Subaru Telescope
• Thirty Meter Telescope (TMT)

The Nasmyth design is common for bulky instruments on large telescopes using an altazimuth mount, whereas a variant, the coudé design, is common for those using an equatorial mount.