Sigma 120-300mm f2.8 EX DG OS HSM S Canon and Nikon mount lens review: Prime image quality in a zoom?By Kevin Carter - Friday October 25 2013 Lens Review
Sigma 120-300mm F2.8 DG OS HSM S Canon Versus Tamron SP 70-200mm F/2.8 Di VC USD Canon
One of the best performing telephoto zooms
Compared with the Tamron 70-200mm f2.8, the Sigma is just ahead in overall image quality when mounted on the Canon EOS 5D Mk III. Both achieve a similar overall score for sharpness, but the two perform differently. Where the Tamron is bitingly sharp at 70mm, levels drop off quite considerably at the longer focal lengths. The Sigma on the other hand is consistently sharp throughout and is actually sharper at 200mm and onwards, and with lower distortion. That works well for the Sigma, where performance at the longer-end is often most needed but difficult for makers to achieve.
Sigma 120-300mm F2.8 DG OS HSM S Canon Versus Canon EF 300mm f/2.8L IS II USM Versus Canon EF 135mm f/2L USM
Very close to the IQ of best telephoto Canon primes:
The Sigma also performs well against the high-performing Canon 300mm f2.8L and 135mm f2.0L models. It comes very close to the performance of Canon’s premium 300mm even at full-aperture, though, as you might expect, it’s not quite at the same level. Even if it can’t quite match the 300mm the Sigma isn’t far off the 135mm f2.0. It has similar levels of sharpness and slightly better illumination at f2.8. However, bear in mind the 135mm is brighter, and better corrected for distortion and chromatic aberration.