Now that I have my production 1DmkIV I've been looking for a good ultra-wide solution for it's 1.3x crop. I think I've found the solution, you can read about it on my blog here The Tokina 11-16 f2.8 – Getting Wide and fast on a Canon Eos 1DmkIV DSLR News Shooter (http://www.dslrnewsshooter.com/2010/01/03/the-tokina-11-16-f2-8-getting-wide-and-fast-on-a-canon-eos-1dmkiv/)

Dan