Id like to get a new general-purpose lens for my EOS 400D, with a budget of about £300, but am in two minds over zoom versus fixed focal-length. Basically, Im asking about digital vs optical zoom. Ive always thought that cropping a wide picture is not as good as zooming the lens to the size you want, but is that in fact true, especially with SLR lenses, given that zooming is always an optical compromise? What I mean is, if I bought say a 50mm fixed lens and used Photoshop to crop to 200mm, would that give better quality than using a 50-200mm zoom? I know there are other issues, such as portability/weight (which doesnt worry me much), and the fact that you cant get wider than than the lens minimum FL (which does worry me a little). An alternative Im considering is the Sigma 18-200mm stabilised lens, which does give wide angles. Does anyone know much about that? Thanks in advance.