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......when I do get one I'll probably go for the 150mm Sigma.
A wise move. I have had a Sigma 180 EX Macro since my 35mm days.
It is a fabulous lens, razor sharp, and excellent contrast, but.... it is now a little long for the digital format. Camera shake is more noticeable at the now longer working distances.
I did try the Canon 100mm Macro, but found it too short for the warier insects, although fabulous for those you could get close to. If money were no object I would get a 150mm tomorrow, but I have also bought a long lens this year (Sigma 500mm f4.5 - stunning piece of glass) and the Boss would not understand!!
Roger Harding