Optical and scientific instrument makers, including telescopes, binoculars, theodolites, latter cine cameras, projectors and precision engineering equipment; based Munich; founded by Traugott Lebracht Ertel (1778-1858); sons Georg Ertel (1813-63) and Gustav Ertel (b.1829) latter joined firm, becoming T Ertel und Sohn; purchased in 1890 by August Dietz (1848-1920), who retained name; incoroporated 1911 as T Ertel und Sohn GmbH; likely producing cine cameras and projectors as Ertel-Werke or Ertel-Werk fuer Feinmechanik during 1920s and 1930s; produced Enigma code machines during the second world war; supposedly still active in Munich in 1983 producing theodolites.