Re: minimum DOF prime lenses?
 

85mm on a full frame camera is my "go to" interview lens. I find that f/2 to f/4 gives a pleasing DOF. It really depends on how much light you have, how far away the background is, and how much you want to blur it. If the background is a fountain, you might not want to blur it too much. If the background is a messy office, blur the heck out of it! :)