My parents are going to Africa for a little over 2 weeks for a trip and are wanting to borrow my 20D. I don't have a zoom lens so they are wanting to buy one. I have come up with two that I think will be ok for the price they are wanting to spend. I'd say $400 MAX. How do these lenses compare? Anyone had any luck with them? I'd love for them to get the 70 - 200 f/4 Canon but I can only find them for $500 and up used.