Canon FL lens mount

Canon FL refers to a lens mount standard for 35mm single-lens reflex cameras from Canon. It was introduced in April 1964 with the Canon FX camera, replacing the previous Canon R lens mount. The FL mount was in turn replaced in 1971 by the Canon FD lens mount. FL lenses can also be used on FD-mount cameras.
Many mirrorless interchangeable-lens cameras are able to use Canon FL lenses via an adapter.
FL lenses.
Standard (50–60mm).
Source:
Canon released 3 'levels' of standard lenses (exc. macro). The f/1.8 lenses were small and lightweight, f/1.4 were mid-range, and the f/1.2 were professional level (top of their line). 