What is depth of field (DOF)?
Depth of Field (DOF) is the area covered in your photo that is “In Focus”. It is also the distance between the nearest and the farthest object that are in focus.
Depth of field is determined by three factors:
From the attached diagram (Fig. 1), we notice that light is reflected off any subject is refracted through the camera lens and propagated on the film plane (or camera sensor in digital cameras).
The two shaded blue triangles determine the area of sharp or close to sharp focus and is called the depth of field.
Areas before or after those triangles are considered out-of-focus.