High Quality Content by WIKIPEDIA articles! In optics,particularly as relates to film and photography, the depth of field (DOF) is the portion of a scene that appears acceptably sharp in the image. Although a lens can precisely focus at only one distance, the decrease in sharpness is gradual on each side of the focused distance, so that within the DOF, the unsharpness is imperceptible under normal viewing conditions. In some cases, it may be desirable to have the entire image sharp, and a large DOF is appropriate. In other cases, a small DOF may be more effective, emphasizing the subject while de-emphasizing the foreground and background. In cinematography, a large DOF is often called deep focus, and a small DOF is often called shallow focus. The DOF is determined by the subject distance (that is, the distance to the plane that is perfectly in focus), the lens focal length, the lens f-number, and the format size or circle of confusion criterion.