http://www.dxomark.com/Reviews/Sigma-120-300mm-f2.8-EX-DG-OS-HSM-S-Canon-and-Nikon-mount-lens-review-Prime-image-quality-in-a-zoom
i have pointed to some other reviews of this lens also, i really like it a lot and i think you should give it a good look if it suits your needs.
dxo ranks it #1 on the 5diii for zooms
i have pointed to some other reviews of this lens also, i really like it a lot and i think you should give it a good look if it suits your needs.
dxo ranks it #1 on the 5diii for zooms