Early Telescope Designers
William Herschel (1738 - 1822)
Replica of Herschel's favorite telescope-- the 6-inch,
7-foot reflector he used to discover Uranus.
William Herschel was a music teacher when, in the spring of 1781, he discovered the planet Uranus. The following year, an impressed King George III appointed him King's Astronomer. From then on, he devoted most of his time to astronomy, supplementing his income by constructing and selling telescopes. He built over four hundred during his lifetime.
Herschel's early telescopes were simple Newtonian reflectors, including his favorite instruments, a six-inch reflector with a focal length of seven feet and an 18½" reflector. It was the smaller of these scopes that he used to discover Uranus. But as Herschel's scope projects grew in aperture size, he began experimenting with the design. He was dissatisfied with speculum metal's low reflectivity and its tendency to tarnish.
With his largest telescope, the 40-foot reflector pictured, he solved the problem by eliminating the secondary mirror entirely, looking directly at the primary's image. He tilted the 49½" mirror so that it could be viewed without blocking the light path. Despite the telescope's nearly unmanageable size and weight, it was an immediate success in terms of production. Within its first month of operation, Herschel had discovered two new moons orbiting Saturn.
William Herschel's largest telescope had a 49½" primary
mirror. It saw first light on August 28, 1789. During that first
session, Herschel described a previously unseen moon
of Saturn.
A little over 150 years after his death, The William Herschel Telescope saw first light in 1987. With an aperture of 165" it was at the time the world's third largest single aperture mirror.