All time devoted assistant Fluffy is holding one of my favorite lens for portrait sessions. The Canon 85/1.2L is a great quality short telephoto lens. The lens produce an extremely shallow depth of field that throws away any background objects out of focus in medium light. I love the fact that it works perfectly without using a high noise ISO like 1600 or 3200 as well.
What I do in general is to focus on subject's eyes and hoping the viewers to accept the rest of the image rendered slightly soft.