In article <5g3jhi$ea6@nuscc.nus.sg>, imakhs@leonis.nus.sg says...

>This lens was made in 6 different versions (optically maybe 4 versions):
>
>2.8/180mm A (some people say it had ED glass already)
>ED 2.8/180mm Ai
>ED 2.8/180mm Ai-S (same optical design as ED- Ai above)
>AF-ED 2.8/180mm Ai-S (smooth plastic surface, optical design changed)
>AF-ED 2.8/180mm Ai-S (rough surface, may have been changed optically)
>AF-D ED 2.8/180mm Ai-S (rough surface, latest version, I think it has not
>been changed optically)
>
>They are all good optics, won't see any much differences on the pictures.

I agree (except that the IF [AF] version is better near minimum focus
at wide apertures) - but you forgot the earliest version: a 180mm f2.5 Nikkor...
Hope This Helps