Hi, I was wondering what you all thought the best macro/zoom lens (something in the 18-400mm range...? I know that's a very wide range, but actually it just needs to go up to at least 200mm) for a Canon Rebel Xsi is in this price range... I'd like a lot of clarity/sharpness and hopefully a large aperture for low-light situations... I have been looking at some Tamrons which look really nice, but if you have some ideas, please let me know! Thanks!!