Since I haven't been able to buy any lenses for an SLR, well... ever I want to make sure I get the best one for me. I posted for opinions earlier and thanks to all the advice I got, I have decided on a 70-300. The only problem is, I am idiot about this and I don't understand all the differences between three I found. The camera is the Rebel T1i, just FYI. First there is the Sigma 70-300mm f/4-5.6 DG APO Macro Telephoto Zoom Lens for Canon SLR (If I understand, its the cheapest one, but with no IS) Next there is the Canon EF 70-300mm f/4-5.6 IS USM Lens for Canon EOS SLR (this one is cheaper, but bigger than the next one, but what is the dif. between the 4-5.6 of this one and the 4.5-5.6 of the next one??) and finally the Canon EF 70-300mm f/4.5-5.6 DO IS USM Lens for Canon EOS (the most spendy, but smaller than the above one) Sorry for my dumbness and thanks to anyone who has an explanation!!