Question: What Japanese brand-name lens was used between 1940 and 1980 by the German camera company founded by Ernst Leitz?

Context paragraphs:
Beier (Beirette): Freitaler Kameraindustrie Beier & Co was an East German camera manufacturer from 1923 to 1989.  Woldemar Beier (1886-1957) opened a camera factory in Freital on 1 April 1923, initially producing plate cameras of wood, then aluminium from 1929, 35mm cameras from 1932 and single lens reflex from 1938.  In 1941 the factory converted to production of parts for bombers and submarines.  In 1945 the machinery was moved to Ulyanovsk, but production resumed in Freital with a variety of small items such as potato peelers, pots and cigarette rolling machines.  Camera production resumed in 1949.  The company was part nationalised in 1959 and fully nationalised in 1972, when it was renamed VEB (citizens' own company).  Beirette compact cameras were produced from 1958 to the 1989, when production became part of the Praktica range.  Several versions were sold as the Boots Beirette.

Rokkor: Rokkor was a brand name used for all Chiyoda Kōgaku Seikō and later Minolta lenses between 1940 and 1980, including a few, which were marketed and sold by other companies like Leica.  The name was derived from the name of Rokkō (六甲山), a 932 m high mountain, which could be seen from the company's glass-making and optics factory at Mukogawa near Osaka, Japan.  The company's founder wanted the name to symbolize the high quality in optics.

Leica M3: The Leica M3 is a 35 mm rangefinder camera by Ernst Leitz GmbH (now Leica Camera AG), introduced in 1954.  It was a new starting point for Leitz, which until then had only produced screw-mount Leica cameras that were incremental improvements to its original Leica (Ur-Leica).  The M3 introduced several features to the Leica, among them the combination of viewfinder and rangefinder in one bright window, like on the Contax II, and a bayonet lens mount.  It was the most successful model of the M series, with over 220,000 units sold by the time production of the M3 model ended in 1966.

Leica Freedom Train: The Leica Freedom Train was a rescue effort in which hundreds of Jews were smuggled out of Nazi Germany before the Holocaust by Ernst Leitz II of the Leica Camera company, and his daughter Elsie Kuehn-Leitz.

Leica Camera: Leica Camera AG is a German company that manufactures optics and high end cameras.  The company was founded by Ernst Leitz in 1924.  The name Leica is derived from the first three letters of his surname (Leitz) and the first two of the word camera: lei-ca.

Walter Mandler: Walter Mandler (10 May 1922 – 21 April 2005) was a famous lens designer of Ernst Leitz Canada (Leica Camera) in Midland, Ontario.

Leica M2: The Leica M2 is a 35 mm rangefinder camera by Ernst Leitz GmbH of Wetzlar, Germany, introduced in 1957.  Around 82,000 M2s were produced between 1957 and 1968.  Around 1500 M2s were produced by Ernst Leitz Canada, but most of these are not marked as such on the top plate.

List of Leica cameras: This is a list of Leica cameras.  Leica Camera AG is a German optics company which produces Leica cameras.  The predecessor of the company, formerly known as Ernst Leitz GmbH, is now three companies: Leica Camera AG, Leica Geosystems AG, and Leica Microsystems AG, producing cameras, geosurvey equipment, and microscopes, respectively.  The Leica cameras are grouped by camera model and year of release.

Leica Standard: The Leica Standard, Model E was the fourth version of the original "35 mm" Leica camera to be launched from Ernst Leitz in Wetzlar, Germany.  The concept was conceived by their employee Oskar Barnack in 1913.  Production of the camera began in 1925 but it wasn't until the end of the decade that it was perfected and full-scale production was established.

Leica copies: Leica copies originate from the Leica camera that was launched by Ernst Leitz, Wetzlar in 1925; it uses the "35 mm" perforated film.  The design was carried out by Oskar Barnack, beginning in 1913 by building a camera for "24×36 mm" negatives that by now is called the "Ur-Leica"; but Ernst Leitz did not decide to manufacture it until 1924.  Once started, the Leica production volume doubled each year; in 1929, some 16.000 cameras were produced.  In 1930, an improved model with interchangeable lens was introduced, followed a year later by the fully developed "Leica II" with standardized film to lens flange distance, and in 1932 the basic "Leica Standard"; the Leica concept was established.  This camera's features are the basis for defining a Leica copy.

Supporting paragraphs: Rokkor Leica Camera
Answer: Rokkor was a brand name used for all Chiyoda Kōgaku Seikō and later Minolta lenses between 1940 and 1980