• Auto-focus works off of contrast in a scene. If you are trying to take a portrait then focus on the eyes not cheecks.
  • Focus is determined only by distance so you can focus on one thing and keep the shutter release pressed halfway and recompose without losing focus. This is a hugely important point.
  • Auto-focus is not half as bad as auto-exposure.
  • BTW, Auto-exposure is set as 'M' via your program dial on the camera and 'Auto\manual-focus' option is set via a small button generally to the left on the top side of your lens.