How do you like the mp-e65? Ive heard its a very hard lens to master.
It is a love/hate relationship
the tech in it is very old. The new cameras out strip its ability (post pros helps a lot) I really wish that Sigma would make a lens like it using the tech in the f/1.4 50mm. I have one of those and it is an awesome lens.
The 65 has a very steep learning curve. I handhold 95% of the shots I take with it. Even the beat of your heart throws the shot off at mag greater than 3:1 so you learn to trigger between heart beats. It took a solid month of using it everyday (200-400 shots) before I started to get passable shots. That was three years ago.
But it is the only game in town for quality hi mag in the field, a bellows rig just does not cut it for slogging through the swamp