Originally posted by bschriver11 The leaning trees are from distortion and while some lenes may handle that better than others it is normal for an ultra wide lens. They will be more noticeable on the edges and extreme corners of the frame, how you frame your shots can either help hide the distortion somewhat or accentuate the distortion for a dramatic effect. There is a learning curve if your not familiar with ultra wide angle lenses.
Definitely. Distortion is made worse if the camera is not perfectly level. IF there is tilt, rotation, the distortion will appear really unnatural, even unsettling. This is due to distortion, a lens characteristic (but generally it is worse with wider lenses) and perspective itself (again, connected to FoV). UWA lenses are attractive because they are so different from the human eye, but that is a downside, as well. And 11mm is really, really wide, so it will have a steep learning curve.
Edit: Honestly, to people new to UWA I usually recommend Samyang 16mm, because it is really wide, but not awkwardly wide. 14mm, 12mm, 11mm, 10mm... these are extremes and are not easy to master