Alvan Clark & Sons

Alvan Clark & Sons was an American maker of optics that became famous for crafting lenses for some of the largest refracting telescopes of the 19th and early 20th centuries. Founded in 1846 in Cambridgeport, Massachusetts, by Alvan Clark (1804–1887, a descendant of Cape Cod whalers who started as a portrait painter, and his sons George Bassett Clark (1827–1891) and Alvan Graham Clark (1832–1897). Five times, the firm built the largest refracting telescopes in the world. The Clark firm gained "worldwide fame and distribution", wrote one author on astronomy in 1899.

The 18.5 in Dearborn telescope (housed successively at the University of Chicago, Northwestern University and Adler Planetarium) was commissioned in 1856 by the University of Mississippi. The outbreak of the Civil War prevented them from ever taking ownership. As a result, it was being tested in Cambridgeport when Alvan Graham observed Sirius B in 1862.

In 1873 they built the 26 in objective lens for the refractor at the United States Naval Observatory. In 1883, they build the 30 in telescope for the Pulkovo Observatory in Russia, the 36 in objective for the refractor at Lick Observatory was made in 1887, and the 40 in lens for the Yerkes Observatory refractor, in 1897, only ever exceeded in size by the lens made for Great Paris Exhibition Telescope of 1900.

The company also built a number of smaller instruments, which are still highly prized among collectors and amateur astronomers.

The company's assets were acquired by the Sprague-Hathaway Manufacturing Company in 1933, but continued to operate under the Clark name. In 1936, Sprague-Hathaway moved the Clark shop to a new location in West Somerville, Massachusetts, where manufacturing continued in association with the Perkin-Elmer Corporation, another maker of precision instruments. Most of Clark's equipment was disposed of as scrap during World War II, and Sprague-Hathaway itself was liquidated in 1958.

File:Alvan Clark 4 Inch Refractor Engraving.jpg|4" telescope at Rockford University, 2021. File:Alvanclark-leah.jpg|8" telescope at Chabot Space and Science Center File:Percival Lowell observing Venus from the Lowell Observatory in 1910.jpg|24" telescope at Lowell Observatory File:Usno-telescope-equalized-1.png|26" telescope at United States Naval Observatory File:Yerkes 40 inch Refractor Telescope-1897.jpg|40" telescope at Yerkes Observatory, 1897 File:Yerkes 40 inch Refractor Telescope-2006.jpg|40" telescope at Yerkes Observatory, 2006 File:Harvard Clark 9-inch.jpg|The 9-inch Clark Refractor at Harvard Observatory, 2015 File:HarvardClark7.jpg|The 7.5-inch Clark telescope dome at Harvard, in 2016 File:Jewett Observetory 12 inch telescope.jpg|12" telescope at Jewett Observatory at Washington State University, 2024