SIGMA 20mm f1.8 EX DG   v    ZEISS DISTAGON T* 28MM F/2.8

Something of a torture test for the Sigma 20 with its much wider FOV (58.7 degrees compared 43.8 -*1.6 sensor). However, the resolving power of the Sigma holds up very well against the highly regarded Zeiss 28. The Sigma is predictably softer in the corners at F/2.8 (Partly due to the distance difference between centre and corner with a wide field of view lens and a fairly close flat target)- but at F/8 the difference between them across the field is negligible. On a full frame camera this may not hold true with regards corner performance.

The Sigma has a tendency to be slightly yellowish in colour (which can be offset - when shooting raw - by applying a cooler WB). Zeiss colour is brighter and very slightly cool.

Test image using a Canon 10D. Same shutter speeds, white balance etc, mirror lock up and focused with a split image screen.

Full resolution crops from centre to top right.