I purchased this lens because of the price point instead of the Nikon of similar specifications. As long as you use it in the middle f-stops rather than wide open it works well for the price. My only complaint is the amount of chromatic aberration that it has in the blue wavelength.

I bought this not long ago and I am not disappointed but there are some issues... Firstly there is a lock that allows you to lock the zoom to 18mm, it is not a problem that has any effect on the use but it is absolutely useless. Secondly the autofocus speed is a little slow, this is due to the lack of a silent-wave motor or equivalent (on the other hand not having an internal engine make the lenses more durable). And finally the focus ring rotates with the autofocus, sigma could do better than that.
It still has great optic quality at an exelent price.

By Alex from West Jordan on 7/10/2007

Way more inexpensive than the nikon counterpart but does the job well.