A ring on the body of an optical instrument, especially a camera lens, which is rotated to focus the instrument (typically by adjusting the relative position of the lenses).
Origin
Late 19th century; earliest use found in The Official Gazette.
Definition of focusing ring in US English:
focusing ring
noun
A ring on the body of an optical instrument, especially a camera lens, which is rotated to focus the instrument (typically by adjusting the relative position of the lenses).
Origin
Late 19th century; earliest use found in The Official Gazette.