What is the origin of 'sleep tight'?
Read moreOne of the mysteries of the English language finally explained.
A type of catadioptric telescope used solely for wide-angle astronomical photography, with a thin glass plate at the front to correct for spherical aberration. A curved photographic plate is placed at the prime focus inside the telescope.
1930s: named after Bernhard V. Schmidt (1879–1935), the German inventor.