Nikon Nikkor Ai 20mm f4
A direct Ai upgrade from the previous K model. Some have serial numbers belonging to the K series. These are not AI conversions, and were probably factory made using up older parts.
130001 < 130087 – 140763 >
1977 - Jan78
Article at Photography in Malaysia site
Review by Fredrik Rasmussen
Review by Ken Rockwell
Development of Nikkor 20mm f4 at Nikon site