Focus limiter for faster focusing

Many of the telephoto and macro lenses in the Canon EF lens range feature a focus limiter switch that’s located near the AF switch. This focus limiter option allows you to narrow the range over which the AF system searches (hunts) and helps to speed up focus. For example, when using the EF400mm f/4 DO IS USM lens – if you know you will not be focusing closer than 8m, you can switch the limiter to 8m to Infinity and eliminate the 3.5m to 8m focus range of the lens.
EF Lenses