Making a simple convex lens from rock crystal has been known from before recorded history, and various descriptions exist of early isolated attempts to make usable telescopes. The effects of pinhole and concave lenses were writen about in the Book of Optics by Arabian astronomer and mathematician, Ibn al-Haytham (Alhazen), around 1020 CE.[1][2] The idea of an "observation tube" without lenses also dates back to the works of Albatenius and al-Biruni.[3]
The telescope reached a state of development that led to rapid and spectacular advances in astronomy only when Dutch-made telescopes, following Lippershey's design of a convex main lens and a concave eyepiece lens, became widely available in Europe in 1608. Galileo greatly improved upon this same design the following year. In 1611, Kepler scientifically explained how a telescope could be made with two convex lenses. A telescope made using his design was first built in 1630, and by 1655 Huygens was building powerful and unwieldy Keplerian telescopes with compound eyepieces, to study the planets.
The reflecting telescope was invented earlier, in the 16th century, by English surveyor Leonard Digges. But it did not become widespread at the time. Digges also probably put together two lenses to make a refracting telescope, but if so it was not commonly used. In 1616, Nichoḷ Zucchi constructed a reflecting telescope with which he discovered the bands of Jupiter in 1630. But it was relatively impractical.
Newton designed a reflector in about 1668 with a small flat diagonal mirror to reflect the light 90 degrees to an eyepiece mounted on the side of the telescope tube. He presented a working example to the Royal Society in 1672, with a spherical mirror of 1 1/2 inch diameter and 6 inch focal length, made of low reflectivity (about 16%) bronze speculum metal. Laurent Cassegrain in the same year described the design of a reflector with a small convex hyperboloidal secondary mirror placed near the prime focus, to reflect light through a central hole in the main mirror.
But it wasn't until 49 years later in 1721, when mathematician John Hadley showed how, in practice rather than in theory, to produce much larger paraboloidal mirrors (initially about 6 inches in diameter), that Newtonian reflectors began to proliferate. And it was much later that anyone made telescopes to Cassegrain's design. Cassegrain's and Newton's are still among the most commonly used types of reflecting telescopes today.
The doublet achromatic lens, the kind still used in most modern refracting telescopes, first appeared in a 1733 telescope made by Chester Moore Hall, who did not publicize it. John Dollond independently developed achromatic lenses, and produced telescopes using them in commercial quantities starting in 1758.
The first radio telescope went into operation in 1937. Since then a tremendous variety of complex astronomical instruments have been developed.
