Achromatic telescope c. 1770 Dollond London
Inv V08699

Telescopes with lenses had problems with colour mixing, making the image blurred. This is called technically chromatic aberration.
As a solution Newton devised the reflecting telescope. He was convinced that the lens problem could not be solved. Still the lens telescope retained its appeal.
In around 1740 the English jurist Chester Moor Hall discovered that the problem could be solved by placing two lenses, one concave and one convex, close behind each other in the eyepiece. He himself could not grind lenses and had to subcontract the work. So as not to reveal his discovery he had the convex lens ground by one optician and the concave by another. Unfortunately the opticians were not very co-operative and the desired result was not achieved.
As a result the name of John Dollond is linked to the invention of the telescope without chromatic aberration. This former silk weaver made his first telescope in 1758.