John Dollond, English optician, c 1750s.
© Science Museum / Science & Society Picture Library
Later engraving by J Poselwhite from a mid-18th century original of John Dollond (1706-1761). The son of a Huguenot refugee, Dollond had been silk-weaver but in 1752 he joined his son Peter in busines as an optician. Dollond invented achromatic (almost colour-free) lenses for refracting telescopes and microscopes. Isaac Newton had thought chromatic aberration (colour fringes in images produced by a simple lens) were inherent. Dollond also invented the heliometer, a telescope used for finding the angular distance between two stars.