 To focus a distant object ("s"1 ≈ ∞), the rear nodal point of the lens must be located a distance "s"2 = 50 mm from the image plane.To focus an object 1 m away ("s"1 = 1,000 mm), the lens must be moved 2.6 mm farther away from the image plane, to "s"2 = 52.6 mm.The focal length of a lens determines the magnification at which it images distant objects.