Double-Gauss lens (English Wikipedia)

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cosina.co.jp

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US patent 399499, Alvan G. Clark, "Photographic Lens", issued 1889-March-12
US patent 583336, Paul Rudolph, "Objective Glass", issued 1897-May-25
US 2019985, Horace William Lee, "Lens", published November 5, 1935
DE 485789, published Sep 30, 1927
DE 439556, Albrecht Wilhelm Tronnier, "Photographisches Objektiv", published 30 April 1925
US 3451745, Tomokazu Kazamaki & Yasuo Takahashi, "Large aperture seven-lens objective lens system", published June 24, 1969, assigned to Asahi Kogaku Kogyo Kabushiki Kaisha

Anonymous. "ОПТИЧЕСКИЕ СХЕМЫ ОБЪЕКТИВОВ MINOLTA MC/MD ROKKOR" [The optical schemata of Minolta MC/MD Rokkor lenses]. Retrieved 25 January 2010.

Anonymous. "AF-S NIKKOR 50mm f/1.4G". Retrieved 4 January 2010.^{[permanent dead link‍]}
"AF Nikkor 50mm f/1.4D". Nikon Imaging. Archived from the original on 2011-02-20. Retrieved 2010-07-01.

"Canon Serenar 28mm f/3.5 I Block Diagram". Canon INC. Archived from the original on 23 May 2013. Retrieved 26 December 2012.
Anonymous. "Lenses (FL Mount): FL50mm f/1.4II: specifications". Canon Camera Museum: Camera Hall. Archived from the original on 24 February 2010. Retrieved 7 January 2010.
Anonymous. "Lenses (EF Mount): EF50mm f/1.2L USM: specifications". Canon Camera Museum: Camera Hall. Archived from the original on 22 October 2007. Retrieved 4 January 2010.
Anonymous. "L&VM standard- Lens". Archived from the original on 26 December 2009. Retrieved 4 January 2010.
"AF Nikkor 50mm f/1.4D". Nikon Imaging. Archived from the original on 2011-02-20. Retrieved 2010-07-01.

Keppler, Herbert (May 2007). "Inside Straight: Optical Miracle: The amazing story of the Biotar". Popular Photography & Imaging. Vol. 71, no. 5. pp. 32–33. ISSN 1542-0337.