I've got one, I believe there were quite a few variaties made all with different performance. Mine is the 28-105 F2.8-3.8 Macro focusing Zoom with a filter thread diameter of 67mm, No. 09045409.
The lens is a vari focal type, in that as you zoom it goes completely out of focus and needs to be refocused. Close focus is very good all the way upto approx 90mm.
Lens performance is good, always used to produce punchy, sharp slides on my film slrs, but I stopped using it because of a couple of problems.
1. Badly affected by glare, I always use a lens hood with it (as with all my other lenses - sad but that's me)
2. exposure inaccuracy, I could never get it to work properly at the long end it always under exposed by a small amount. I've assumed it's something to do with electrical contacts not passing through the right info. Perfect exposure at the wide end.
I bought it because at the time it had a review in a lens magazine that had it out performing the Angenieux zoom and all others at F8. I'll be honest at the time I had no idea there were different versions and I bought the lens when the lens review came out, so always assumed it was that one!
These days it sits in the back of a cupboard because it has some fungus growing on the front element.
--
Walt
http://picasaweb.google.com/waltdall