I'm looking for a new Macro lense and am considering the 100mm Canon offering as well as the 180mm. I also noticed the Sigma 180mm and was wondering if anyone had used this? I need to know if it would be useable as a portrait lense as well as a macro and take the MT-24 EX series flash. I know the 100mm Canon offering would be ideal as it would do both. The cost of the Sigma caught my eye though Thoughts anyone?