The Grad filter i use is a cokin pro z (link here http://amzn.to/Vo46PR ) it fits on my canon 16-35 full frame lens with the canon 5dmark 2. you need to buy lens rings to get it to fit the same size of lens you are using more details and links in the blog here
Adapter ring 77mm http://amzn.to/ZPajYB and 82mm adapter ring http://amzn.to/11y85Jq
