A short history of the Telescope by Mary Bellis

" Phoenicians cooking on sand discovered glass around 3500BCE, but it took about 5000years more for glass to be shaped into a lens for the first Telescope. A spectacle maker probably assembled the first Telescope. Hans Lippershey(c1570-c1619) of Holland is often credited with the invention, but he was almost certainly not the first to make one. Lippershey was however, the first to make the new device widely know. The Telescope was introduced to Astronomy in 1609 by the great Italian scientistGalileo Galilei, who became the first man to see the craters of the moon, and went on to discover sunspots,the four large moons of Jupiter,and the rings of Saturn.Galileo's Telescope was similar to a pair of opera glasses in that it used an arrangement of glass lenses to magnify objects. This arrangement provided limited magnification- up to 30 times for Galileo-and a narrow field of view;Galileo could see no more than a quarter of the Moon's face without repositioning his Telescope.
In 1704, Sir Issac Newton announced a new concept in Telescope design whereby instead of glass lenses, a curved mirror was used to gather in light and reflect it back to a point of focus.This reflecting mirror acts like a light-collecting bucket: the bigger the bucket,the more light it can collect.The reflecting Telescope which Newton designed open the door to magnifying objects millions of times--far beyond what ever could be obtained with a lens.
Newton's fundamental principle of using a single curved mirror to gather in light remained the same.The major change that took place was the growth in the size of the reflecting mirror, from the 6" mirror used by Newton to the 6-meter(236" in diameter)mirror of the Special Astrophysical Observatory in Russia, which opened in 1974.
The idea of a segmented mirror dated back to the 19th century,but experiments with it had been few and small, and many astronomers doubted its viability.It remained for the Keck Telescope to push the technology forward and bring it into reality the innovative design.