The NIKKOR-N Auto 24 mm f/2.8, released ca. 1970, its the first lens equipped with the Close-Range-Correction Mechanism. It is a 7-group, 9-element retrofocus type lens.

The focusing of the close-range correction system, the most important feature of the lens, is carried out by separating the lens into two lens groups between the sixth lens element and the seventh lens element, and by narrowing the separation between the two lens groups upon focusing.

(Taken from Tale 14 : NIKKOR-N Auto 24 mm f/2.8 by OHSHITA, Kouichi.)