History of the telescope
The earliest known telescope appeared in 1608 in the Netherlands when an eyeglass maker named Hans Lippershey tried to obtain a patent on one. Although Lippershey did not receive his patent, news of the new invention soon spread across Europe. The design of these early refracting telescopes consisted of a convex objective lens and a concave eyepiece. Galileo improved on this design the following year and applied it to astronomy. In 1611, Johannes Kepler described how a far more useful telescope could be made with a convex objective lens and a convex eyepiece lens and by 1655 astronomers such as Christiaan Huygens were building powerful but unwieldy Keplerian telescopes with compound eyepieces.
Leibniz Institute for Astrophysics Potsdam
The first new instruments were delivered in the spring of 1914. The 65 cm refractor — the first big astronomical instrument manufactured by the famous enterprise of Carl Zeiss Jena — was mounted in 1915, whereas the completion of the 122 cm reflector telescope was delayed until 1924 by the First World War. Struve died in 1920 from an accident, and his successor was Paul Guthnick, who introduced in 1913 photoelectric photometry into astronomy as the first objective method of measuring the brightness of stars. When the 122 cm telescope (at this time the second largest in the world) was finished, the Babelsberg Observatory was the best-equipped observatory of Europe.