Today I conducted further tests of my favorite prime - the Canon 85mm f/1.8 - in natural light. To get dramatic results you must shoot wide open, or nearly wide open. But you must also be careful with such a narrow depth of field - it's easy to miss focus. f/2.5 gave me precisely what I wanted. Notice that the plane of her face is in focus, while her earrings are not.
Notice also that I broke the rule of thirds by placing her in the center of the frame. My excuse: the flowers in the foreground partially obscure her face and create depth, like a curtain. A curtain of flowers.