This short focus lens has a whopping f/1.8 aperture and a full-frame coverage. While those data are impressive, optical quality at the corners is a bit bad, as the tests below show. I've tried to use it on a Canon 5D at f/4 under a very dark sky and the resulting images show a bit of corner distortion, visible in the high res files (Gegenschein and Milky Way).
But the field where this lens perform best is in the time-lapse imaging, where a fast stop is fundamental. I'm using this lens with a Canon 350D stopped down to f/2.5, and I'm very happy of the results.