Stepping motor Canon EF lens mount

canon ef 40mm f/2.8 stm pancake lens

canon announced stepping motor (stm) lenses first in june 2012, alongside eos 650d/rebel t4i/kiss x6i.

canon stated technology allows smooth , silent autofocus, , compatible bodies (the first of 650d) provide continuous autofocus in live view , video. unlike usm, stm lenses use focus-by-wire enable full-time manual mode. 2 main disadvantages linked focus-by-wire: first, need computationally process input before intended action executed leads perceptible lag. second, using motor requires power, when stm lens not connected camera or camera switched off, changing focus impossible.

all ef-m lenses introduced date—the ef-m 22mm pancake prime , ef-m 18–55mm zoom introduced eos-m, plus later 11–22mm, 15–45mm, 18–150mm, , 55–200mm zooms, , 28mm macro lens—feature stm technology.

all stepping-motor lenses marked letters stm on front of lens part of model designation.