3Dkraft (Click here) posted a detailed comparison between the Zeiss Loxia 2.8/21 vs Otus 1.4/28 vs Sigma Art 20/1.4 bs Zeiss 16-35mm FE vs Color Scopar 21/4 vs Ultron 21./1.8. And he writes:
The Zeiss Loxia 2.8/21 is propably the best compromise between size, weight, low light capability and optical performance. It is a perfect fit for the A7-series, has excellent edge and border performance right from open aperture, rich colors and contrast, excellent back and stray light resistance due its perfect coating and it has a weather sealing. Some users critisize that there is only a small part of the barrel that you can grab when you mount it to the camera body. In the near range, it also provides nice options to play with a shallow depth of field. This little gem seems to be worth every cent you pay for it, if you like the 21mm viewing angle.
Loxia 21mm store links: [shopcountry 46456]