I was talking with a fellow T2i owner over on my Facebook page and he was wondering how to get the blurred background on his photos. I thought it would be beneficial to share our conversation with all of you...
Joser's Question: I just got the T2i with an 18-55mm lens and was wondering how I could get the blurry background on all my pics!?
Moose's Answer: The only way to do it with your 18-55mm lens is zoom to 55mm and create some space between you, your subject and the background. To really capture a shallow depth of field (small area in focus), you'll need a lens that can obtain an aperture f-number between f/1.4 and f/2.8. Unfortunately, your kit lens only goes down to f/3.5 at 18mm and f/5.6 at 55mm.
The the "nifty fifty" Canon 50mm f/1.8 is an excellent starter lens if you're interested in isolating subjects against a silky smooth background. Not only is this lens super affordable, but it will allow you to do things that just aren't possible with your 18-55m kit lens. More specifically, it'll allow you to capture a very shallow depth of field (small area of focus) which really makes portraits pop and jaws drop. :)