Focal length detector of a camera having a zoom lens

摘要

A focal length detector of a camera having a zoom lens includes a brush having three sliding contacts which are electrically connected to one another; a code plate having three code patterns and a ground pattern, the code plate and the brush being moved relative to each other according to a variation of the focal length of the zoom lens; and a focal-length detecting circuit which is connected to the three code patterns and the ground pattern. The ground pattern always contacts a specific sliding contact of the three sliding contacts. The three code patterns are arranged so that the three code patterns come into contact with the remaining two sliding contacts in predetermined combinations when the code plate and the brush are moved relative to each other.