Uniform Scale

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Glossary Terms

The Uniform Scale (or US) is an old way to give the aperture settings of a lens. The following table gives the correspondence between regular f-stops and US stops:

US stop F-stop
1 4
2 5.6
4 8
8 11
16 16
32 22
64 32
128 45
256 64

The Uniform Scale was introduced in the 1890s.[1] It was still used by some unscrupulous manufacturers in the 1950s, to make the lenses seem wider than they actually were: for example a lens marked as "US 3.5" has about f/8 maximal aperture. (See the Koniken for an example.)


  1. According to this post at the Large Format photography forum.