Hi there! I actually had posted a thread recently on which lense to buy as I plan to backpack abroad coming up very soon. I own the Canon 30D with the 17-85 IS kit. My hope is to supplement this lens with a longer zoom. I received some great feedback from photographers suggesting the 70-300 DO, 70-200 IS L 2.8 and even the 100-400 L. What I found inteesting is that many had suggested the a 50 prime. Why is that? What would be the advantage of owing a 50 prime. Is it increased picture quality, or greater creative presence from that larger aperature? Thanks a million! it is appreciated!