Hello all, i've searched the forums and haven't quite found an answer for my question. I have a canon rebel xsi (i think it's 400d) and am looking for a wide angle lense. I have the kit lense as well as the 70-300mm f/4-5.6 is usm. I shoot alot in the mountains when i'm backpacking where there is low light. I was looking at two lenses although i really don't want to spend as much as the more expensive option. I am looking at the 17-40mm f/4l and the 16-35mm f/2.8l. The second is about twice as much but it may prove crucial if i'm shooting in the backcountry. I was wondering your advice on these lenses or maybe even a suggestion for another lense. Thanks.