Compared with the high-end Zeiss Touit 1.8/32, the Sigma has the lower image quality overall. Although the two have comparable homogeneity in sharpness across the field (which could be better), the Zeiss is sharper. Both lenses exhibit slight barrel distortion though the Sigma’s is milder. However, even though the Zeiss is faster it has slightly lower levels of chromatic aberration and far better control of vignetting, though the latter is easy to remove in post. Bear in mind the Sigma is around $650-700 less than the Zeiss.