Dual Pixel CMOS AF is an autofocus technology developed by Canon that aims to deliver the speed and responsiveness of phase detection autofocus using only the camera sensor and not a separate phase detection sensor. This has many advantages for mirrorless cameras and DSLRs being used in live view mode. Effectively, the photosites on Canon’s sensor are split into two, and the two ‘halves’ can be used to measure the distance of the subject by how much the two halves are ‘out of phase’. Other makers have their own on-sensor phase-detection autofocus systems. It erodes one of the few remaining advantages of DSLR cameras over mirrorless models.
STM stands for stepper motor lenses, a new type of autofocus motor used by Canon in some of its lenses. Stepper motors offer fast, precise and quiet focus adjustments, so these lenses are well suited both to regular stills photography and to video, where autofocus noise can be picked up very easily by the camera’s internal microphone. Canon’s STM lenses work very effectively with cameras using Canon’s Dual Pixel CMOS AF autofocus system.
See also: Autofocus basics