As these photographs were taken at 12mm there is a degree of distortion.
I have an old Sigma 12-24 left over from when I used Canon bodies. I am now trying to decide if I should keep it or replace it with a Sony 12-24 lens. Unfortunately the Sony lens costs not much less than Euro 2000.
Yesterday I used the Sigma for the day and was surprised by the lack of distortion and then I discovered that the camera had been set to crop-mode. Today I made another attempt and was not happy about the amount of distortion and unfortunately am no closer to making a decision.