All of the lenses on test have a similar widest focal length, but the results show a difference in performance throughout their focal ranges.
The Canon and Nikon lenses show similar characteristics, but both suffer from visible barrel distortion at their widest focal lengths.
The Sony and Tamron optics have excellent centre and middle frame sharpness, but at 16mm and 24mm this softens towards the edge, and distortion is apparent at the widest focal lengths, with signs of fringing.
The Tokina lens produces average results for sharpness, but results for fringing and distortion are good. The Olympus lens produced the lowest sharpness results, with visible softness and fringing at the widest focal length.
At the top of the group are the Sigma 18-50mm and Pentax 16-45mm. Both show excellent sharpness at all focal lengths and only some slight distortion. The blue edge fringing of the Pentax means that the Sigma just beats it.