I have seen three versions of the 50mm f1.8 AIS Nikkor:
- The icky plastic current version.
- The metal compact version (virtually identical to late "E" barrel,
except that all the barrel parts are metal [this lens is a favorite
of mine, though it is slightly less sharp at wide apertures than:]).
- The original, larger version.
(The last is the sharpest, but has some barrel distortion. the newer two
have the same optics as the AF and E, and have no distortion, and are
multicoated [The E isn't multicoated, and is a convenient lens to pair
with the AF to show what little advantage there is in multicoating a
well-designed lens]. The newer two are unique in the Nikon line in that
they are AIS, but do not have the coupling prong. [Though the 500mm P
may share this "distinction".])

>What I find interesting is the variation in the 50/1.8 Nikon Series E
>lenses. Some of them are obviously cheaper version with plastic
>barrels, but some seem identical to the Nikkor 50/1.8 AIS with the
>metal barrel and aluminum DOF ring in the middle of the barrel. I have
>a couple of these at the moment, and it is interesting how VERY
>different they are. I suspect that Nikon may have relabeled some
>Nikkor 50/1.8N lenses as Series E. The fact these "better" E lenses
>even have the rubber focus ring, and look very unlike the other
>Series E lenses is sure strange.

There were two styles of fixed focal-length E lenses:
- The truly ugly all-black plastic barrel original version.
- The later version with finer detailing, chrome ring, and rubber
covered focusing ring.