Page "Newtonian telescope" Paragraph 6

Like Gregory before him, Newton found it hard to construct an effective reflector.

It was difficult to grind the speculum metal to a regular curvature.

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.

Because of these difficulties in construction, the Newtonian reflecting telescope was initially not widely adopted.

It wasn't until 50 years later in 1721 that John Hadley showed a much-improved model to the Royal Society.

Hadley had solved many of the problems of making a parabolic mirror.

His Newtonian with a mirror diameter of 6 inches (~ 15 cm ) compared favorably with the large aerial refracting telescopes of the day.

The size of reflecting telescopes would subsequently grow rapidly, with designs doubling in primary mirror diameter about every 50 years.