There are four key parameters you need to set to achieve sharp focus. Here’s a quick summary; I’ll explain all of these in more detail later in this section.
Focus mode. Whether your camera operates in autofocus, manual focus, or autofocus/manual fine-tuning modes. (AF, MF, AF+MF)
Autofocus Operation. Whether the camera locks in focus when you press the shutter release halfway, or continues to refocus as the subject moves. (One-shot, Servo)
AF (Autofocus) method. Determines whether the EOS M should hunt for and track human faces, ...