I likely wouldn't have purchased an ultra-wide lens such as this if it wasn't for the Canon digital EOS D30 camera. In brief, this lens has minimal linear distortion and a great resistance to flare. You can read my preliminary write-up on this lens to understand why I purchased it, rather than Canon's 14mm. 3.2 While a highly versatile lens I've never been totally happy with the overall image quality. I've read other's comments to this effect.
Some folks claim to be satisfied.
But, the lens has pretty good flair characteristics and distortion is low. The front element doesn't rotate when the lens is focused, making it well suited to the use of a polarizing filer though care needs to be exercised at the widest end, both due to vignetting with any attached filter and uneven polarization. There is provision for rear-mounted gelatin filters as well. Image quality is high and I have used this lens numerous times to obtain images that would otherwise have required a much larger camera with movements. Focusing is manual.