From Canon T3i to Nex-6. Am I giving up some image quality?

The biggest difference seems to be lens speed (2.8 vs 1.8). The 24mm lens isn't rated very high by professional reviewers and it's overpriced for what it is.

The 24mm has better build quality, than the inexpensive Sigma, and I'm not saying it's a bad lens but I don't think it's much more than adequate. Like many lenses, the faults are corrected by in-camera programs.

I apologize for saying this but I've been unimpressed by most of the pictures taken with the Sony/Zeiss that have been posted to this forum.

It's biggest advantage appears to be it's 1.8 maximum aperture.