I bought this used lens and it is almost like new. I started playing with it and I can only get it to focus properly 50% if the time. I micro adjusted it, but it's still back/front focusing or not focusing well at all. I'm thinking of sending it to Canon. Do any of you have any experience with this and how much it would cost? I focused on the face. As you can see it is really bad but the other photo is ok.