I am looking for a prime to be used on a 40D. I will use it for low light portraits around the house, andfor school plays. I have rented the 135L once, and fell in love with it. It is expensive however compared to the 100f2, and if I went with the 100f2, I could also get a 580EXII which I could really use. Obviously the reach of the 135L will help at school but it will hurt in closer quarters. Anyone have experience with these two lenses? Will I be disappointed with the 100 after using the 135L? I would love to see some comparison photos of real subjects.