The 20mm lens may seem very wide but on the APS-C sensor, it's equivalent to 30mm; a mini wide angle. It's wide enough as a normal wide angle, but not so wide that's it's hard to control. The Canon 20mm f2.8 is quite a nice lens. I intended to test its edge performance today, so that I can compare it to the Sigma 19mm f2.8. At wide apertures, the Canon FD 20mm f2.8 seems a bit better at the corners. In fact, it almost as good as the center (not true outer edges of course, due to the crop sensor of the NEX-6), but the 19mm Sigma has an adge in the middle, which is very sharp at f2.8. I think the bokeh is also nicer on the Sigma at wide open. Over all, I enjoy using the Canon FD 20mm f2.8 lens. It's nicely build and focuses very smoothly, and optically very good.
Bokeh - NEX-6 & Canon FD 20mm f2.8. Click for larger.
Waiting - NEX-6 & Canon FD 20mm f2.8 @ f2.8. Click for larger.
Taxis - NEX-6 & Canon FD 20mm f2.8.