the depth of composition of a shot, i.e., where there are severalplanes (vertical spaces in a frame): (1) a foreground, (2) a middle-ground, and (3) a background; depth of field specifically refers to the area, range of distance, or field (between the closest and farthest planes) in which the elements captured in a camera image appear in sharp or acceptable focus; as a rule of thumb, the area 1/3 in front of and 2/3 behind the subject is the actual distance in focus; depth of field is directly connected, but not to be confused withfocus
— Film Terms