DOLLOND , JOHN

Dollond was born in London, the son of Huguenot refugees. He started life as a silk weaver but later joined his eldest son, Peter, in making optical instruments, and devoted years of experiment to developing an achromatic lens. The problem confronting lens makers at the time was chromatic aberration – the fringe of colors that surrounds and disturbs images formed by a lens. This put a limit on the power of lenses (and of refracting telescopes), for the stronger the lens, the more chromatically disturbed the images became. Chromatic aberration is caused by the different wavelengths that make up white light being refracted to different extents by the glass, each being focused at a different point.

In 1758 Dollond succeeded in making lenses without this defect by using two different lenses, one of crown glass and one of flint glass (one convex and one concave), so made that the chromatic aberration of one was neutralized by the aberration of the other. In fact he was not the first to make such a lens, since Chester Hall had already done so in 1753, but Dollond managed to patent the idea because he was the first to publicize the possibility.

In 1761 he was appointed optician to George III but died of apoplexy later that year.