Sigma 24-105mm F4 DG OS HSM A Canon mount lens review: A new standard?By Kevin Carter - Monday December 16 2013 Lens Review
When compared against the Canon 24-105mm f4L, to be fair an aging model now, the Sigma outperforms it in several key areas. It has higher peak sharpness at every focal length and at the initial aperture it has better corner sharpness at the longer end of the zoom, which is a limitation of the Canon equivalent.
Another benefit is the just over +1/2 stop improvement in Transmission. But while distortion is similar the Canon has a slight better control of vignetting and slightly lower lateral chromatic aberration.
Compared to the 24-70mm f4, the Sigma exhibits the same characteristics as it did with the 24-105mm, notably that it’s sharper and more uniform across the frame throughout the range at the wider apertures. In all other respects the 24-70mm has a slight advantage. It has less distortion, lower vignetting and better control of CA, though at 24mm it’s noticeable in the extreme corners at every aperture.