You are looking at 2 different lenses here, the left one is New-Nikkor 35mm f/2.8 with an Ai-ring and the other one is the early Nikkor 35mm f/2.8 Ai with a non-Ai ring. I swapped the rings and it seems that they’re identical. I don’t know why they share the same barrel design but the only reason I can see here is Nikon’s trying to save money.Most AI lenses share the same barrel design as the New Nikkor version, because essentially they are the same lens, so it is natural the aperture rings could be swapped. The AI version just has the new AI aperture ring, new style of rubber grip, and the rear lens protector has the maximum aperture post added (later used by FA for matrix metering).
The confusing thing is that there are two versions of the AI 35/2.8. The first is based on the New Nikkor, with 6/6 elements. This one has small front and rear elements which is probably why vignetting is on the high side. DOF lines are on the barrel under the focus ring and the focus throw is reasonably long. In my experience this one is sharp and has almost no barrel distortion - the least distortion of any 35mm I have tried.
After a couple of years production the AI version was replaced by an all-new design with 5/5 elements. This was probably cheaper to build, with fewer elements and no thick pieces of glass like the old version. The barrel is slightly longer but still a compact lens. The front and rear elements are larger so vignetting is reduced. It has some barrel distortion but it is mild and even. Sharpness is good, maybe not quite as good as the previous version, but my feeling is the rendering is a little rounder - background bokeh is smoother. This one has DOF marks level with the focus ring and a very short focus throw.
The AI-S version is based on the 5/5 AI lens. The focus throw is longer than the AI version but still much shorter than the older 6/6 version. Overall this is the best of the 5/5 versions due to the longer focal throw, and I think the styling is more attractive.
