Sigma 50mm 1.4 soft?
Agreed. I had several lenses with my Rebel and just bought the DA35mm for my K-5. None of them are as sharp wide open, although some are better than others. I believe the softness on many is actually spherical aberation, the hazy look that blurs edges when wide open. Combine this with slightly missed focusing and it will look very soft. DOF at F/1.4 is pretty thin.