Here is a lens I got from a repairman maybe a decade ago as part of a fairly large lot of stuff he was selling. For years I've meant to do some work on it, but I never did, so now it is going to be somebody else's turn. It is a Sigma 18mm in Nikon mount and has both AI and non-AI ability. Sigma called this model the XQ Filtermatic. Here are the three most important things I'm going to say about this lens:
1. It really should be serviced. The elements look ok but have a haziness that needs to be cleaned. The 4 filters (they're internal and there are yellow 48, light blue 180, orange 56 and clear 1A) still function ok but seem to be cloudy also. To me, the orange one seems like it may have some fungus, but without taking the lens apart I can't say for certain. You get aperture selections between 2.8 and 22. Focus action is stiff, but I'd guess the lens has not been used in probably 12 years or more. Both caps come with it. And I was given an internal spacer ring the fellow thought I should have. You'll get that, too.
2. For somebody who wants to service/clean this, I believe you'd wind up with a very interesting and unique fast wide angle lens...certainly for black/white work. New it was quite expensive. In the late 1970s I think the price was around $400.
3. Can you take a picture using this lens "as is?" Yes, aside from the stiff focus it is usable. In fact, I attached it to an adapter and took a picture this morning with a Canon 350D dslr.
$30 plus the cost of actual postage.
PayPal ok for international buyers but check/cash/money order for people in the USA please.
If questions, please ask.
Jon