Summary: I can't write about the optics yet, as I just received this lens. However, I get the idea of caveat emptor when you buy used, but the casing is so worn it's difficult to see the numbers. Not only is there no lens hood included as promised, there isn't even a cap for the lens mount.
Summary: This lens is a good solid one. I got the best results using shutter priority but I use Manual 90% of the time. It has nice colors but you can ALMOST get similar results with a kit lens with the right lighting. It is up from three stars because of how it feels on the camera.
Into the Looking Glass (with apologies to Alice living in Wonderland)
InHisHand "planted-in-the-mid-west", Amazon
2 February 2012
Summary: Believe it or not, Alice, I connected this low-end Sigma to my 5D Mark II (full frame) for comparison against the Canon 24-105 f4L. My results: this Sigma lens compares favorably, with caveats.
Summary: This lens has surpassed my expectations. It is a very good light lens. The lens does not hunt to autofocus. It is fast enough on the telephoto end (f4 at 70 mm) that I use this lens as my general walkaround lens.