I did test the lens on a N80 and yes, it would just quit focusing at some point. Removing and reseating the lens reinialized the focusing and all was well. Sigma states in the directions that come with the lens certain models will not AF in the Nikon line. They do say it will work with the F5, F4 series, N70, F90S, F90, and Proneia 600 and all others manual focus only. However with my D100, so far it has worked perfectly. Lets hope it continues to do so. I will contact Sigma support and see if they do have an update or fix for this problem.