Near depth of field

Description

In optics, particularly as it relates to film and photography, depth of field (DOF) is the distance between the nearest and farthest objects in a scene that appear acceptably sharp in an image. Although a lens can precisely focus at only one distance at a time, 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.
For a given symmetrical lens the near depth of field, is the distance from the camera to the nearest limit of depth of field and is depended to the object distance , the lens focal length and the f-number.
(The f-number of an optical system is the ratio of the lens’s focal length to the diameter of the entrance pupil).