Don't mean to thread jack but I just bought a Canon rebel xsi also and I was playing around with some lenses and stuff that I had, and I put this "fisheye" wide lense on the end of the lens and I tried messing with it flipped around on both sides of the fisheye lens.

Now my camera can't focus on anything! The red dot's don't show up, and everything close up and far away is blurry as hell. HELP PLEASE!!! I'm a nubix cube with Camera's/