The Sigma 12-24 is an excellent ultrawide. It is very sharp with very little barrel or pincushion distortion. It is a true 12-24 fullframe with a film SLR (love it with my Nikon N80) or full frame digital slr, and effectively an 18-36 with an APS-sized sensor digital SLR. Excelleent ultrawide for architecture, landscapes etc. At 12mm though, it is so wide that you must be careful of distortion introduced by shooting off-level. This is not to say this particular lens is faulty and distorts, but would be true of any ultrawide lens with this wide degree of coverage. While I have heard much talk of supposed poor Sigma quality control, I have no qualms at all about this lens - It is sturdy, tough, smooth and has performed flawlessly for me for years.