Mechanism for rotating a cam barrel of a zoom lens

A zoom lens comprising:

• a plurality of lens frames guided in a direction of an optical axis without rotating about said optical axis;
• a plurality of cam followers formed on each of said plurality of lens frames which extend radially outwards at an equi-angular intervals about said optical axis;
• a cam barrel having a plurality of cam grooves which are formed on an inner peripheral surface of said cam barrel, said plurality of cam followers being respectively engaged in said plurality of cam grooves, said plurality of lens frames being moved in said optical axis direction without rotating about said optical axis to change a focal length of said zoom lens by rotation of said cam barrel;
• a rotational barrel positioned around said cam barrel and driven to rotate about said optical axis;
• a plurality of rotation transmission grooves formed on an outer peripheral surface of said cam barrel at an equi-angular intervals about the optical axis to extend parallel to said optical axis;
• and
• a plurality of inward projections formed on an inner peripheral surface of said rotational barrel to be engaged in said plurality of rotation transmission grooves, respectively.