Dollond, John (1706–1761)
John Dollond was an English optician who introduced achromatic lenses for telescopes and microscopes. A London-born son of immigrant Huguenots
from France, Dollond took up the weaving trade of his father, but at the
age of 46 joined his son Peter in the optical business. In 1752 he became
involved in a controversy over the question of whether Isaac Newton had been correct in asserting that it was not possible to combine two lenses
of different materials to obtain an achromatic lens (a lens that focuses
all colors of light equally). Even though Dollond was supposedly an uneducated
optical worker, he stood up to Leonhard Euler, one of Europe's most learned
mathematicians. And when he did experiments with prisms of different materials
he proved Newton wrong by demonstrating that a prism combination could be
found that gave refraction without dispersion.
This opened the door to making greatly improved telescopes. By combining
two lenses with the proper curvatures, one of crown
glass and the other of flint glass,
he and his son could make telescope objectives that didn't have the usual
blurring that results from a variation of the focal length with color.
There was a controversial claim that, in 1729, an English barrister named
Chester Moor Hall had designed the first achromatic lens and that Dollond
may have known about it. However, Hall never submitted a claim for his invention
nor did he attempt to publicize it, and there is no doubt that Dollond was
the first to make successful achromatic telescopes in quantity and offer
them commercially. The firm of Dollond & Son became the preeminent English
telescope-makers and telescopes made by them went to all parts of the world.
After John died in 1761 the business flourished through four more generations
of Dollonds. In 1871 the business went out of the family but continues to
this day as Dollond & Aitchison.