STM

A challenge of shooting high definition video with EOS cameras has been achieving continuous autofocus. In response, new Canon EF, EF-S, and EF-M lenses now offer a stepping motor (STM) drive, designed to deliver smooth and quiet continuous AF during video shooting when paired with the Movie Servo AF feature on the EOS Rebel T4i and the EOS M Digital Camera. Decades of proven optical expertise allow Canon to incorporate the right type of stepping motor for each lens. The EF 40mm f/2.8 STM utilizes a gear-type that allows the lens to achieve an ultra-compact and lightweight design; whereas the EF-S 18–135mm f/3.5–5.6 IS STM uses a lead-screw type, which prioritizes AF performance, offering the smoothest and quietest operation. The lightweight EF-M 18–55mm f/3.5–5.6 IS STM uses a lead-screw and rack type system, providing extremely quiet and smooth Movie Servo AF for optimal movie shooting.