A new AI-s version of the previous 16mm f2.8 was introduced in 1982.
AI-S had sn >185001. The differences with AI versions are small but the optical construction was slightly different, as well as the new external look with a smaller focusing ring (only 2 rows of rectangular checkers in the rubber), and also a new coating was applied to the glasses.
The precious metal cap was lately replaced by the 61mm push-on, the same used on the 16mm AFD and on the 10.5mm f/28 G.
Filters are 4, rear bayonet-type: L1BC on the lens (later becoming L37C), O56, A2, B2 inside a blister included in the package, and named CA-2. The blister is in a kind of faux leather that degrades in time and for unknown environmental reasons.
NEVER BUY A 16MM 2.8, IN THE AI, AI-S, OR AFD VERSION IF IT HAS NOT THE L37C FILTER ON THE REAR LENS. It will affect field curvature and focus capabilities because it is PART OF THE OPTICAL DESIGN.
- as always a great loads of infos on MIR website
- A nice review by KenRockwell from an expert photographer perspective, even if not from a panoramic photographer he has a valuable approach in evaluating lenses.