Conclusion - Pros
* Decent image quality
* Low vignetting even on full frame
* Fast and positive autofocus
* Very good build quality, excellent tripod collar design
* Low price
Conclusion - Cons
* Relatively weak at 200mm (softness, chromatic aberration, pincushion distortion on full frame)
* Unconvincing 'macro' performance; soft at wider apertures, significant focus shift on stopping down
* Red/cyan bokeh chromatic aberration
Overall conclusion
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.
However this lens does have some problems, mostly related to its sub-par macro performance. Image quality when shooting at short focus distances with wider apertures is distinctly weak, with a combination of general softness, focus shifts due to spherical aberration, and red/cyan fringing around slightly out-of-focus regions (due to axial chromatic aberration) giving very unconvincing imaging indeed. Sigma appears simply to have been over-ambitious in its bid to extend the close focus distance from the original 70-200mm F2.8 EX design, and perhaps allowed the marketing value of that 'Macro' tag to drive the specification somewhat further than ideal for the lens formulation. This is unfortunate, because it mars the performance of an otherwise impressive lens; it is also potentially something of an own-goal, as buyers may well judge the lens based on casual test shots taken at close distances, and be distinctly unimpressed.
Of course a key determinant of the overall performance of a fast telezoom lies in the focusing system, and here the Sigma does not disappoint. The near-silent hypersonic motor delivers fast, accurate and consistent autofocus, including when shooting in low light or tracking moving subjects, and feels no less speedy or responsive than the Canon or Nikon systems. Manual focus works well too, with a decent focus ring travel allowing high levels of precision, and full-time override of autofocus available. Overall build quality is also very good, with a high standard of fit and finish, and the particularly well-designed tripod collar will be a welcome bonus for shooters who swap their cameras on and off supports on a regular basis.
Overall, if you appreciate the limitations of this lens and stick within its practical limits, it provides much of the performance of the camera manufacturers' equivalents at a much lower price. Potential buyers will also inevitably compare it to the Tamron SP AF 70-200mm 1:2.8 Di LD (IF) Macro, and here the choice essentially boils down to the superior optics of the Tamron versus the Sigma's excellent autofocus system. Indeed ultimately that hypersonic motor is the Sigma's strongest selling point, so if you're looking for a budget fast telezoom for low light or action work, then this is the lens for you.
