In article <4sevc9$p7h@newsbf02.news.aol.com>, shem99@aol.com says...

>I just bought a used 28mm/2.0 Nikon AI lens which seems to be in good
>shape, but the lens seems to rub when I focus. It's not horrible and it
>seems even throughout the focusing range. Is this something I should
>worry about?

Sounds like dry lubrication - it should be serviced, if so, or the focus helical may wear faster than normally. If there is no looseness to the lens
front when gripped and wobbled, or play in the focus ring (and the lens checks out fine optically on film, and the price is right for the appearance
condition it is in, and you want to keep it and put an extra [roughly] $75
into it), it may make sense to keep it.
Another possibility can be checked by seeing if a strip of paper will
fit between the focus ring and the front barrel section all the way around
(and that there is no helical scratching on the front barrel section). If
the lens fails this check, it has been dropped, and should be returned.
Hope This Helps