Have you looked at 35mm f2? Supposed to be a good alternative.
I had the 28mm f1.8 on my 5D2 as a wide angle prime lens for landscape work.
Stopped down to f8-11 it was sharp but from f1.8 to f2.8 it was soft in the corners.
I also found it to be not wide enough for my landscape work so in the end I sold it and got a Canon 17-40.
Got it.![]()