This is a fantastic lens, but to be honest I find it difficult to use well. I'm not into portraits - apart from animals, and as animals tend to have long bodies or noses or both it's difficult to utilise the very shallow depth of field - so I end up using it at f4.
Also the auto focus on 5D just cannot cope with the f2 depth of field on a moving subject. So I end up using it at f4.......
I've attached three of my pictures with the 135mm, all using manual focus, the shot at Bramham Horse Trials in England was pre focused. Oh and by the way, I think they are all at f4
it's a specialist lens and tricky. Think I'm going to get a 70-200 instead............................