Tokina AT-X PRO series lenses us what Tokina calls a "One Touch Focus Clutch" mechanism to switch the lens between manual focus and auto focus operation. The Manual focusing ring on Tokina AT-X PRO lenses IS the AF/MF switch on the lens. With the lens mounted on a camera push the manual focusing ring forward, away from the camera until it clicks and the AF can be seen on the lens barrel. To focus manually pull the focus ring back towards the camera until clicks back and only MF can be seen on the lens barrel. The focus can be clicked forward or back from any point in the focus movement.