Nikon's Ai-S 300mm f/4.5 — manual-focus telephoto, the Ai-S version of the earlier Ai lens.
The Nikon Nikkor 300mm f/4.5 Ai-S is the Ai-S version of Nikon's manual-focus 300mm telephoto — providing full Ai-S coupling for programmed auto exposure compatibility. Same optics as the earlier Ai version.
Optically good — sharp from f/8 with 300mm providing useful telephoto reach. The f/4.5 is slightly slower than the f/4 designation that became standard. Ai-S coupling adds programmed auto compatibility over Ai.
Nikon F mount with 72mm filter thread. Approximately 900g. Ai-S coupling. Full-frame coverage. Same optics as ID 1192 Ai version but with improved coupling.
Available used very cheaply. The AF and AF-S 300mm f/4 versions are dramatically better. The Ai-S coupling is the upgrade over the Ai version. For manual-focus telephoto on film or adapted mirrorless.