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Dolland, John

colour telescopes achromatic free

(1706–61) British optician: introduced achromatic lenses for telescopes and microscopes.

Dolland was for many years a silk-weaver; he was the son of a French Huguenot refugee. In 1752, however, he joined his son Peter in his business as an optician. They attacked the problem of chromatic aberration, ie the colour fringes in the images produced by a simple lens, which had considered inherent in lenses. In fact C M Hall (1703–71), a London lawyer, had designed a compound lens of crown and flint glass which was largely achromatic (colour-free) and had telescopes made using them, from 1733. The Dollands almost certainly knew of this; however they did much experimental work, secured improved glass and, after John Dolland’s patent of 1758, produced good quality achromats. This led to nearly colour-free refracting telescopes being made; although the reflecting type ultimately became dominant in astronomy, as a mirror is completely achromatic, requires only one flaw-free surface and can be supported from the back. In microscopy Dolland-type lenses were of great value, as there is no easy alternative to a refracting system for obtaining optical magnification in the microscope.

Dolores Claiborne (1995) - Overview, Synopsis, Critique [next] [back] Doll, Sir Richard

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