After taking some night skyline shots of Minneapolis I noticed I had a little problem. I manually focused the shots at infinity and they came out unfocused (not camera shake blurriness) and I was far enough away to get the entire skyline in the frame. I then went to test out my lenses to see what was going on in the daytime and I actually have to focus forward slightly in order to get the sharpest image. Is this supposed to happen or might there be a problem with my lenses? I'm using a Canon EOS500D and my lenses are the kit EF-S 18-55 f/3.5-5.6 IS and the EF-S 55-250 f/4-5.6 IS, I seem to have this problem with both.