Nikkor was a tad worse than Zeiss but still better than Sigma. The Sigma was definitely better than the oldest of them all, the Canon 24-70 mm, for a change. Even if we take into account the fact, that the Canon was tested on a sensor the least densely packed with pixels, so we would have to increase its MTF 50 values by 10%, the results are still worse at all focal lengths. Do not forget that the Sigma is the cheapest, the smallest and the lightest lens of all compared here so it deserves a round of applause. Looking at the real images you can hardly notice any difference between this lens and the Nikkor or the Zeiss – if you do notice it, it will be only at maximum aperture.