Does anybody have or have used a Sigma 50mm f/2.8 EX DG Macro? I just found a very good condition used one on ebay, which expires within the next 24 hours. Any reviews or information on this lens would be greatly appreciated! What are it's macro capabilities? Is it a true macro 1:1 lens? I have done a very small amount of research on this lens, but what i've seen looks very promising for the cost. Thanks!