Hi, I was wondering if anyone could help me. I'm not very technically minded when it comes to cameras but I do love photography. I'm thinking of getting a zoom lens for my Pentax K100D Super but I need to have something with a max zoom of about 500-600mm. Preferably not a fixed length either say something like 150-500mm? I do like Sigma and have a 70-300mm lens but need something bigger and better as I would like to get some really good bird photos from hides and such like. My budget isn't massive I'd say no more than £300 so I think it may be a bit naive of me to expect to get something ace with that amount of money. Can anyone recommend a good lens?