This little gem is a sleeper! Looking for a lightweight, ultra wide, I picked this lens up, hoping it would work for landscape and architectural work. It has passed all my tests so far, but keep in mind I shoot on tripod, and at f8-11 only, so no test for background blur and wide open, as I dont care about those f stops.
Do not pass up a chance to test this lens instead of buying 24L, as in some cases, it is sharper. And it fits in a pocket, and is a great companion lens to the 35mm 2.0. This is also much better in my opinion than the 17-40 zoom which I sold to buy this and the 35 2.0.
Stopped down, it shows excellent edge to edge sharpness, good CA and distortion control. I am very happy with it.