Driving the RF-S 3.9mm f/3.5 STM Dual Fisheye is a gear-type stepping motor (STM) with a dual-lens autofocus mechanism, which moves the left and right lenses in unison. This makes autofocus as simple to operate as it is with an ordinary lens. The electronic focusing/control ring and the left-right focus difference adjustment switch enhance operation by allowing adjustment of the left-right focus differential.
Autofocus operates only on subjects within the image circle of the left lens. Additionally, Servo AF is not available. Before shooting a movie, you must adjust the focus to One-Shot AF or manual focus.