I've used Sigma lenses as long as I have been a photographer. Yet I wonder if there really is a difference between Sigma and Tamron brand lenses and which one is better. If one is noticably better than the other, how does it stack up to consumer Canon lenses? Also, how much better are consumer Canon lenses compared to professional Canon lenses? I'm a college student, so my options are limited. I can't go out and buy these lenses and try them all out so I am seeking the opinions of the people here. Thank you!