the telescopic zoom lens type and a cam mechanism for it

Lens barrel comprising: first, second and third cylinders (19, 17 and 16) concentrically arranged in this order from an optical axis; at least one cam slot (17b) formed on said second barrel (17); at least one guide groove (16c) formed on the inner periphery of said third barrel (16); at least one follower (18, 19a) formed on the inner periphery of said first barrel (19) and cooperating with said at least one guide groove through said at least one cam slot; and at least one element formed integrally on the outer periphery of said second cylinder adjacent one end of said at least one cam slot, said at least one element being shaped with a clean surface to contact said at least one follower.