And so. I took this model to replace a similar tamron without a stub. I came across thiscompy with a pronounced back focus. if it were not for the 7d camera in which there is an adjustment, I would have thrown this lens to hell. Many people write that HSM is fast almost like USM garbage ! once again I wascomnvinced of the opposite. the tamron was faster, although it squealed. andcomped better with focusing in dark places. The picture is juicier and the bokeh is nicer at 50mm F2.8 on this sigma. In general, a good staffer if there are no problems with focus. pics