Originally posted by rkymtnrider Thank you both for your insight. If you have a moment could you explain why the 20mm lens is desirable and the other two aren't? Thank you.
The other two are just run of the mill consumer grade zooms, the 28-80 isn't a "bad" lens, it is just worthless because it came with just about every auto focus body sold. It is the 18-55mm of its day. The Sigma is the same deal, it was the cheap lens that a lot of people got as their first telephoto zoom, again not bad, just not worth very much.
The 20mm is an uncommon focal length to find on film, it was very wide and very expensive in its day. It was also very good, but being that expensive means they didn't sell very many of them and since it is no longer in production the only way to get one is used.
It is just supply and demand.