Newtonian telescope

[8] Diffraction can also be minimized by using a high focal ratio with a proportionally small diagonal mirror mounted on the corrector.

Galileo Galilei and Giovanni Francesco Sagredo had discussed using a mirror as the image forming objective soon after the invention of the refracting telescope,[12] and others, such as Niccolò Zucchi, claimed to have experimented with the idea as far back as 1616.

[15] Newton built his reflecting telescope because he suspected it could prove his theory that white light is composed of a spectrum of colours.

[16] Colour distortion (chromatic aberration) was the primary fault of refracting telescopes of Newton's day, and there were many theories as to what caused it.

[21] He found that the telescope worked without colour distortion and that he could see the four Galilean moons of Jupiter and the crescent phase of the planet Venus with it.

Newton's friend Isaac Barrow showed a second telescope to a small group from the Royal Society of London at the end of 1671.

The surface also tarnished rapidly; the consequent low reflectivity of the mirror and also its small size meant that the view through the telescope was very dim compared to contemporary refractors.

His Newtonian with a mirror diameter of 6 inches (150 mm) compared favourably with the large aerial refracting telescopes of the day.

Woman looking through a Newtonian telescope
Newtonian telescope design
A large Newtonian with ladder to reach the eyepiece
Schmidt–Newtonian telescope.
A replica of a second reflecting telescope Newton presented to the Royal Society in 1672 (the first one he made in 1668 was loaned to an instrument maker but there is no further record of what happened to it). [ 19 ]