John Dollond, English optician, mid 18th century.
© Science Museum / Science & Society Picture Library
Engraving made c 1761 by J R Smith after a painting by B Wilson. John Dollond (1706-1761), the son of a Huguenot refugee, had been a 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 (1642-1727) 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.