I saw this particular lens on ebay, and wanted to know what you guys thought of it. I'm looking for something in that range, but I want to make sure that when I use it all of the functions of the camera are going to work (I'm a bit new to the digital realm). I also saw a Tamron that had the same range. Will everything work the same? Its advertised as Sigma 70-300mm DG lens for Pentax. Thanks for your help!