The Sigma 70-200mm F2.8 EX DG Macro HSM II is a prime example of an independent manufacturer producing a design which can challenge the camera companies' own lenses in most aspects of optical and operational performance, but at a much lower price. In almost all regards it performs well in everyday use, delivering good quality images across a broad range of situations. The optics are perfectly competent, if not outstanding; indeed the lens is really very good towards the short end, but weaker at 200mm, where it's slightly soft and suffers from relatively high levels of chromatic aberration. Vignetting is impressively low, even on full frame (presumably a benefit of that broad and stubby barrel design), and geometric distortion reasonably well controlled. So whilst the Sigma's optics may not be technically quite up to the same standard as the competition, users will find few glaring faults in its performance either.
