F-number (English Wikipedia)

Michael John Langford (2000). Basic Photography. Focal Press. ISBN 0-240-51592-7.
Southall, James P. C. (1910). The Principles and Methods of Geometrical Optics: Especially as applied to the theory of optical instruments. Macmillan. p. 537.
Piper, C. Welborne (1901). A First Book of the Lens: An Elementary Treatise on the Action and Use of the Photographic Lens. London: Hazell, Watson, and Viney. p. 101. "There are three systems of classification according to exposure; one known as the Uniform System (U.S.) of the Royal Photographic Society, in which an aperture of f/4 is taken as requiring a unit exposure. Another is the Dallmeyer System, in which f3.16 [sic] gives a unit exposure. The third is the Continental or International System, also known as the C.I. system, in which f/10 requires a unit exposure. The two former are now practically obsolete, but the third is still in use. Then there are two Zeiss systems, in which apertures are classified according to intensity, f/100 having a unit intensity in the 'old' system, and f/50 in the 'new' system."
Beck, Conrad; Andrews, Herbert (1902). "Section IV: Properties of Lenses; 3. Rapidity". Photographic Lenses: A Simple Treatise (2nd ed.). London: R. & J. Beck Ltd. pp. 96–107.

arizona.edu (Global: 1,592^nd place; English: 1,119^th place)

Greivenkamp, John E. (2019). "OPTI-502 Optical Design and Instrumentation – Radiative Transfer" (PDF). University of Arizona College of Optical Sciences. University of Arizona. Retrieved 2025-07-22.

Harry C. Box (2003). Set lighting technician's handbook: film lighting equipment, practice, and electrical distribution (3rd ed.). Focal Press. ISBN 978-0-240-80495-8.
Paul Kay (2003). Underwater photography. Guild of Master Craftsman. ISBN 978-1-86108-322-7.
David W. Samuelson (1998). Manual for cinematographers (2nd ed.). Focal Press. ISBN 978-0-240-51480-2.
Google search
Ives, Herbert Eugene (1920). Airplane Photography (Google). Philadelphia: J. B. Lippincott. p. 61. ISBN 9780598722225. Retrieved 2007-03-12. {{cite book}}: ISBN / Date incompatibility (help)
Mees, Charles Edward Kenneth (1920). The Fundamentals of Photography. Eastman Kodak. p. 28. Retrieved 2007-03-12.
Derr, Louis (1906). Photography for Students of Physics and Chemistry (Google). London: Macmillan. p. 83. Retrieved 2007-03-12.

"Kodak Motion Picture Camera Films". Eastman Kodak. November 2000. Archived from the original on 2002-10-02. Retrieved 2007-09-02.

Charles F. Claver; et al. (2007-03-19). "LSST Reference Design" (PDF). LSST Corporation: 45–50. Archived from the original (PDF) on 2009-03-06. Retrieved 2011-01-10. {{cite journal}}: Cite journal requires |journal= (help)

Jack (2023-02-26). "Angles and the Camera Equation". Strolls with my Dog. Retrieved 2025-07-22.

Transmission, light transmission Archived 2021-05-08 at the Wayback Machine, DxOMark
Sigma 85mm F1.4 Art lens review: New benchmark Archived 2018-01-04 at the Wayback Machine, DxOMark
Colour rendering in binoculars and lenses - Colours and transmission Archived 2018-01-04 at the Wayback Machine, LensTip.com
"Kodak Motion Picture Camera Films". Eastman Kodak. November 2000. Archived from the original on 2002-10-02. Retrieved 2007-09-02.
"Marianne Oelund, "Lens T-stops", dpreview.com, 2009". Archived from the original on 2012-11-10. Retrieved 2013-01-11.
Charles F. Claver; et al. (2007-03-19). "LSST Reference Design" (PDF). LSST Corporation: 45–50. Archived from the original (PDF) on 2009-03-06. Retrieved 2011-01-10. {{cite journal}}: Cite journal requires |journal= (help)

Greivenkamp, John E. (2004). Field Guide to Geometrical Optics. SPIE Field Guides vol. FG01. Bellingham, Wash: SPIE. p. 29. ISBN 9780819452948. OCLC 53896720.