Depth of Field:
The ‘Depth of Field’ is the distance across the part of the picture that is acceptably sharp to the eye. When a lens focuses on a subject it creates only one point of clarity in the image. There is a gradual fall-off of sharpness either side of that point. Within the ‘depth of field’ the image appears sharp to the eye. The edges of the ‘depth of field’ are defined by the two points where the loss of sharpness becomes noticeable.
Depth of field is sometimes confused with depth of focus. However the two concepts relate to the same phenomenon, but on either side of the lens. Depth of field is used to describe the concept of the sharpness range in the area beyond the lens, outside of the camera. The ‘Depth of Focus’ is used to describe the same phenomenon on the imaging plane (the sensor face). The term depth of focus applies exclusively to the inside of the camera.