Originally Posted by
inkista
The only real exception I'd make to this is if you feel you need an ultrawide lens on your crop body until you can get a 5D. Because of crop body factors, you're simply not going to find a lens that can do that on both a crop and a 5D, and all the crop-body ultrawide lenses are fairly new in design and still retain a lot of value for resale. You are unlikely to find any lens that does the same thing on a full-frame for an equivalent price. Also, if you go with a third-party maker for an ultrawide, it will still mount on a 5D (unlike Canon's EF-S lens), and you only have to worry about vignetting.