I am an oral surgeon who recently bought the Canon Rebel XT with the standard lense, and am considering upgrading to a macro lense and ring light for both my intraoral uses and surgical pictures. I am a poor resident on a tight budget and have been considering the canon ef 100mm f2.8 macro vs. the tamron 90mm f2.8 and also the new sigma 70mm macro lenses. I am also looking to buy a ringlight and am debating between the canon and sigma. I am a beginner and just using the pictures for my own presentations not professional use. Does anyone have some advice onwhich system to buy.