Nikkor 18mm f/4
First production date: 1974
Production change in 1977 to AI design
Last production date: 1982
Lens construction: 13 elements in 9 groups
Filter size: 86mm and/or Series 9
Weight: 350 grams
Minimum focusing distance: 30cm
Uses Nikon lens hood HN-15
Nikkor 18mm f/3.5 (I own and use this lens)
First production date: 1982 (this lens was designed to replace the 18mm f/4)
Lens construction: 11 elements in 10 groups
Filter size: 72mm
Weight: 315 grams
Minimum focusing distance: 25cm
Uses Nikon lens hood HK-7
AI (Automatic Indexing) lenses were designed for cameras such as the FM, FE, and F3.
AIS (Automatic Indexing with Shutter Priority) lenses are designed for cameras with programmed automatic exposure control such as the Nikon N2000, N8008, and F4.
The 18mm f/4 had an AI design and a pre-AI design.
I am not sure if the 18mm f/3.5 had an AI design and an AIS design or only the AIS design.
I am also not sure if the 18mm f/3.5 manual focus lens is still in production or if it has been replaced by the 18mm f/2.8 autofocus