Editing F-number (section)

=== Typographical standardization ===
[[File:Yashica-D front.jpg|thumb|[[Yashica#TLRs|Yashica-D TLR]] camera front view. This is one of the few cameras that actually says "F-NUMBER" on it.]]
[[File:Yashica-D top.jpg|thumb|From the top, the Yashica-D's aperture setting window uses the "f:" notation. The aperture is continuously variable with no "stops".]]

By 1920, the term ''f-number'' appeared in books both as ''F number'' and ''f/number''. In modern publications, the forms ''f-number'' and ''f number'' are more common, though the earlier forms, as well as ''F-number'' are still found in a few books; not uncommonly, the initial lower-case ''f'' in ''f-number'' or ''f/number'' is set in a hooked italic form: ƒ.<ref>[https://books.google.com/books?as_q=lens+aperture&num=50&as_epq=f-number Google search]</ref>

Notations for f-numbers were also quite variable in the early part of the twentieth century. They were sometimes written with a capital F,<ref>{{cite book| url=https://books.google.com/books?id=ypakouuKvwYC&pg=RA2-PA61| format=Google| access-date=12 March 2007| title=Airplane Photography| last=Ives| first=Herbert Eugene| publisher=J. B. Lippincott| location= Philadelphia| year=1920| pages=61| isbn=9780598722225}}</ref> sometimes with a dot (period) instead of a slash,<ref>{{cite book| url=https://books.google.com/books?id=V7MCVGREPfkC&q=aperture+lens+uniform-system+date:0-1930| access-date=12 March 2007| title=The Fundamentals of Photography| first=Charles Edward Kenneth| last=Mees| publisher=Eastman Kodak| year=1920| pages=28}}</ref> and sometimes set as a vertical fraction.<ref>{{cite book| url=https://books.google.com/books?id=AN6d4zTjquwC&pg=PA83| format=Google| access-date=12 March 2007| title=Photography for Students of Physics and Chemistry| first=Louis| last=Derr| location=London| publisher=Macmillan| year=1906| pages=83}}</ref>

The 1961 [[American National Standards Institute|ASA]] standard PH2.12-1961 ''American Standard General-Purpose Photographic Exposure Meters (Photoelectric Type)'' specifies that "The symbol for relative apertures shall be {{not a typo|ƒ/}} or {{not a typo|ƒ:}} followed by the effective ƒ-number." They show the hooked italic 'ƒ' not only in the symbol, but also in the term ''f-number'', which today is more commonly set in an ordinary non-italic face.