I could not find a topic for this lens so here goes. The Sigma 12-24mm is one of the widest non-fisheye lens available for full frame (if not the widest of them all?). I have the original version of this lens, Sigma has also released a newer version of the same lens.
Wide open, the lens is rather soft and really needs to be stepped down to f/8~f/11 to achieve its sweet spot, which is fairly decent when it comes to sharpness. Not unexpected, the IQ fall off in the corners is noticeable. In the range from 14-24mm it cannot compete with the Canon 17-40mm f/4L, the 16-35mm f/2.8L and the Canon 14mm f/2.8L.
However, when using this lens on 12mm as a pseudo prime, it has literally no equal if you discount the Canon 8-15mm f/4L as that is a fisheye. When I use this lens on my Canon 1D MkIII (1.3x crop), I use it firmly at 12mm and I only use it in tight places where any other lens could not frame the entire scene in one shot. Use this lens on a full frame body and you will need to be acutely aware of the position of your feet or they will end up in the shot.
Wide open, the lens is rather soft and really needs to be stepped down to f/8~f/11 to achieve its sweet spot, which is fairly decent when it comes to sharpness. Not unexpected, the IQ fall off in the corners is noticeable. In the range from 14-24mm it cannot compete with the Canon 17-40mm f/4L, the 16-35mm f/2.8L and the Canon 14mm f/2.8L.
However, when using this lens on 12mm as a pseudo prime, it has literally no equal if you discount the Canon 8-15mm f/4L as that is a fisheye. When I use this lens on my Canon 1D MkIII (1.3x crop), I use it firmly at 12mm and I only use it in tight places where any other lens could not frame the entire scene in one shot. Use this lens on a full frame body and you will need to be acutely aware of the position of your feet or they will end up in the shot.