Big lens though. I recently bought one---haven't shot with it yet because I don't have a lensboard to fit, but when I unpacked it I experienced a certain amount of "OMG, what have I done?" angst. I guess it's not really intended for handholding, and in the context of carrying a tripod around it doesn't add that much bulk, but it's a pretty intimidating hunk of metal.
The only downside is that you need either a Speed or similar press camera with a focal plane shutter. Weight aside, they are excellent portrait lenses.