Newton's reflector
Isaac Newton built his reflecting telescope as a proof for his theory that white light is composed of a spectrum of colours.
[6] He had concluded that the lens of any refracting telescope would suffer from the dispersion of light into colours (chromatic aberration).
[4] He devised means for shaping and grinding the mirror and may have been the first to use a pitch lap[7] to polish the optical surface.
The Eye-glass was Plano-convex, and the diameter of the Sphere to which the convex side was ground was about 1/5 of an Inch, or a little less, and by consequence it magnified between 30 and 40 times.
The concave Metal bore an Aperture of an Inch and a third part, but the Aperture was limited not by an Opake Circle, covering the limb of the Metal round about, but be an opake Circle, placed between the Eyeglass and the Eye, and perforated in the middle with a little round hole for the Rays to pass through to the Eye.
By comparing it with a pretty good Perspective of four Feet in length, made with a concave Eye-glass, I could read at a greater distance with my own Instrument than with the Glass.
The telescope had a flat diagonal secondary mirror bouncing the light at a 90° angle to a Plano-convex eyepiece with a probable focal length of 4.5mm yielding his observed 35 times magnification.
Newton said the telescope was 6.25 inches long; this matches the length of the instrument pictured in his monograph "Opticks".
[8] Newton completed his first reflecting telescope in late 1668 and first wrote about it in a February 23, 1669 letter to Henry Oldenburg (Secretary of the Royal Society).".
[9] Newton found that he could see the four Galilean moons of Jupiter and the crescent phase of the planet Venus with his new little telescope.
[8] Newton's friend Isaac Barrow showed the telescope to small group from the Royal Society of London at the end of 1671.
This was something which Newton proposed as an improvement on his second telescope mirror as he found that the metal was too soft due to the silver.
[15] Two replicas were made in the 1960s from the original, one for the Queen and another for European Northern Observatory at La Palma.
