Olympus M.Zuiko Digital 12mm F2.0

When focusing on a subject, there is an area behind and in front of the focused point that is also in focus. This area is called depth of field. The amount of area behind a focused point will always be greater than the area in front of the focused point regardless of aperture. Depth of field becomes deeper when the focal length is short (wide-angle lens), the focusing distance is long and aperture is small.