Robert-Aglaé Cauchoix (24 April 1776 – 5 February 1845) was a French optician and instrument maker, whose lenses played a part in the race of the great refractor telescopes in the first half of the 19th century.
At first Cauchoix produced a wide range of scientific instruments including barometers and micrometers, but he soon specialized in optics, making spherometers and objectives.[1] [2] He made a telescope for the Paris Observatory in 1820 and in 1825 he made a 6.5 inch (16.5 cm) refractor for the observatory of the Collegio Romano, a Jesuit academy in Rome. In the Royal Observatory, Greenwich an 1838 instrument named the Sheepshanks telescope includes an objective by Cauchoix.[3] The Sheepshanks had a 6.7 inch (17 cm) wide lens, and was the biggest telescope at Greenwich for about twenty years.[4]
An 1840 report from the Observatory noted of the then-new Sheepshanks telescope with the Cauchoix doublet:[5]
Although the reflector telescope was invented in the second half of the 18th century, technological difficulties made the refractor the telescope of choice until the mid-1850s. Improvements in lens production, like the introduction of the achromatic lens by John Dollond, spawned an aperture size race that started in the early 1820s with a telescope made by the German optician Joseph von Fraunhofer. Cauchoix must be credited holding the lens size record three times this period. In 1831, Cauchoix made a 13.3 inch (almost 33.8 cm) refractor for the Irishman Edward Joshua Cooper, who used it to observe Halley's Comet in 1835 and a solar eclipse in 1836.[6] [2]
In 1829, Cauchoix made an 11.75 inch lens for a French customer, but sold it to the British astronomer James South. South used it for his new telescope, which he found defective due to problems with the equatorial mount.[2] In 1838, this telescope was dismantled, but the lens by Cauchoix served in other instruments until 1989.