Donat, it is not perfect. It vignettes quite a bit wide open, it has some CA wide open, and, on the A7R, corners are not perfect wide open. But it has such qualities that Lloyd Chambers calls it the best lens ever for Leica M. Even compared to my new Otus 55, its art of colouring is peerless. I call my Otus Bertha, after Big Bertha, the greatest cannon that ever was, because that is how it feels, the biggest and baddest. And I call my ZM Audrey, for Audrey Hepburn: wonderful grace and elegance.So good to have both...