History of the Newtonian Reflector from 1669The Newtonian Reflector was invented by Sir Isaac Newton in 1672 and was the first to feature the revolutionary 45deg; mirror.
When the telescope was introduced to England by Thomas Harriot in 1609 it transformed classical science. For the first time, people could see the lunar mountains, Jupiter's moons, Saturn's rings, and numerous wonders in the Milky Way.
Although these telescopes have been a leap forward, the obstacles imposed by glass-making at the time restricted telescopes to a single lens, no more than 3 inches in diameter with focal lengths around 18m. They had tiny fields of view, dim aberrated images, and low magnification.
For this reason, astronomers began experimenting with mirrors instead. In 1614, Niccolo Zucchi experimented with concave mirrors and concave eyeglasses in search of better pictures than could be obtained with refractors. By the 1660s James Gregory in Scotland and Robert Hooke in London were also testing mirrors, however, it was Isaac Newton's self-made presentation to the Royal Society in 1672 that constituted the real breakthrough.
Stimulated by the works of Gregory and Hooke, Newton set about his research and produced a 1.5-inch tin and copper allow mirror in 1669 and devised a more efficient optical configuration to make use of it. Instead of tilting the mirror or using secondary concave curved mirrors that required several optical surfaces to create an image, Newton had an excellent idea. Why not intercept the light reflected from the concave mirror just short of focus with a second flat mirror set at 45°? The light could then exit the tube through an eyepiece at the side. Newton's primary mirror only had a focal length of 165mm, however with its impressive ball joint mounts and a delicate screw focuser, it performed brilliantly. The Newtonian reflector was born.
Newton's reflector had another huge benefit, that being there was no chromatic aberrations. Without chromatic aberrations, you get an image free from false colour and by bringing all the rays of light into a single focus, it can give sharper results. Chromatic aberrations happen as different wavelengths of light travel at different speeds through the glass - hence the rainbow from a prism.
By 1721, the design had not changed, it just got larger. John Hadley demonstrated a Newtonian reflector with a 6-inch mirror and 6 ft. focal length and boasted a 200x magnification. By 1846, William Lassell discovers Neptune's moon Triton using a homemade editorially mounted 24-inch Newtonian reflector.
More recently, Sir Patrick Moore used his 12.5-inch Newtonian reflector to finish his iconic lunar cartographic work.
