I posted this in the wrong place originally, so I'm going to try again... I'm very new to photography, and I don't want to spend a lot of money. (I know those 2 things cancel each other out, but I want to make sure I really enjoy it before spending a ton of money on it.) Anyway, I'm looking for a macro lens for my Canon Rebel XT. I would like to get a Sigma lens because they're less expensive than the Canon lenses. I have found the 50mm, 100mm, and the 150mm f2.8 macro lenses from Sigma and they seem to be what I'm looking for. However, I'm trying to figure out the real difference between them besides price. I am looking to take pics of flowers, butterflies, etc. Can anyone tell me what the distance from my subject would be on each of these lenses? I think that might help me to determine which would be the best fit. Thanks so much.