One of the advantages of fast prime lenses is that - depending on the focal length of course - they can have a very restricted DoF: and one of the disadvantages is that they can have a very restricted DoF! Mrs S and I have been out and out all day so I took the opportunity to photograph her at short range whilst she was driving to get a better idea of how this would work out in practice.
The point of focus here is on the corner of her eye and you can see that not much else is in focus and this is with the lens stopped down two stops from its wide-open aperture. To get all of her profile in sharp focus, I would have had to have stopped down another two or three stops.
This, of course, is for my PLAY project - you can read more about it in my profile - where I'll be using a different prime lens for each month of the year: in January it's the Nikon 50mm f/1.4G on a full-frame camera (the D610 today).