The sharpness is excellent, beginning with the open. The edges are superior to those produced by a tamron. Stabilizer - I can take a picture of a city at night using only my hands, at a wide angle, using only 1/4 of a second, and it's simple! Even though the bokeh produced by the tokina 16-50/2.8 is generally more interesting, the overall quality of the image produced by the tokina 16-50/2.8 is superior to that produced by the tamron 17-50/2.8. When compared to the tamron and the tokin, the focusing accuracy of the usm motor is pleasing. XA: There exist, but the quantity is significantly lower than that of tokinas; do not steam. I mount it on a Canon EOS 50D and use it there. Everything has been satisfactory, with the exception of the absence of dust and wetness. As for the assembly, it was done so correctly that after a period of six months it did not attract any dust. Despite not having shot any test worlds and not having purchased a lens specifically for this purpose, I did not observe any distortions like as "barrel" or "cushion." I was going to bring my 24-70 / 2.8 L lens, but I realized that I needed a wider angle first, and the 17-55 is the sharpest of the two. I couldn't be happier with this buy. There is no such thing as a perfect tamron-tokin-sigma solution.