(main mirror in a reflecting telescope)
A primary mirror is the main, large mirror
in a reflector telescope, which may have
additional mirrors. The primary mirror
is the first mirror off which the light reflects,
following mirrors called secondary and tertiary.
A telescope with no secondary mirror is called
a prime focus telescope.
Primary mirrors now range up to around 10 meters,
but plans are to build telescopes with primary
mirrors three times that size.
Hobby-Eberly Telescope (HET)
liquid mirror telescope
Origins Space Telescope (OST)
Ritchey-Chrétien telescope (RCT)
Southern African Large Telescope (SALT)