I`m trying to do my homework. I`m thinking of maybe getting a third party lens for a Canon eos 40d instead of the stock lens that comes with the kit. I really like the f/2.8 for the low light pics that I take sometimes. and i just want to keep that option if possible. Plus this seems to be a nice all around range for me for my first lens. my shots will be indoors, low light and some with lamps if needed for other shots. Something in the range of this. 24-70mm f/2.8 L . I want to make sure that I get a lens that will work with the Canon correctly and will auto focus. I don`t know if there is a chart i can follow or if someone can just tell me. Should I just stick with Tamron, Sigma,Tamric, etc. I`m not sure I have all the names right. I`m really new to the third party lens so i need some help here. I just need to be pointed in the right direction with the correct name of the company I should be looking at. Thanks for any info you can send my way.