Can anyone suggest me about what lens should i buy next to use along side with my 24-105 F4L? should i look for a wide angle lens or telephoto lens? i'm using it as a general purpose or walk around use. for wide angle lens i'm considering canon 17-40 F4L and for a telephoto i'm considering canon 70-200 F4L or if anyone have something else to recommend. i have a canon 50d. Thanks for your help