Nikon's original Ai 50mm f/1.4 — pre-Ai-S coupling for the early meter-coupled Nikon system.
The Nikon Nikkor 50mm f/1.4 Ai is the Ai (Automatic Indexing) version of Nikon's 50mm f/1.4 — predating the later Ai-S with its improved coupling. The Ai provides meter coupling on all Ai-compatible Nikon bodies.
Same optical quality as the Ai-S version (ID 817) — sharp from f/2.8 with characterful f/1.4 rendering. Ai coupling provides metering compatibility. Manual focus with smooth Nikon helicoid. The difference from Ai-S is in the mechanical coupling system.
Nikon F mount with 52mm filter thread. Ai coupling — not Ai-S. The Ai coupling provides stop-down and centre-weighted metering. The Ai-S added programmed auto compatibility. Metal construction throughout.
Available used at budget to mid-range prices — slightly cheaper than Ai-S versions. Functionally very similar to Ai-S for manual-mode shooting. Check for oil on aperture blades — common on these vintage Nikkors. For manual-focus film photography.