One of my blog readers, asked if I would write about how I use the 85mm 1.2. He seems to think I have “mastered it”. Let me put that thought to rest right now. No way have I master the 85 1.2. This little lady is just plain tough to use. But there are some things to be aware of. First, remember that between 1.8 and 1.2 your depth of field is very, very shallow.
When I say shallow, I mean one eye in focus and the other eye out or worse, eye lashes in focus and the eye out. Sometimes you can get away with, one eye out and the other in (hmm, that sounded odd), but most of the time it is just uncomfortable to view. If there is any trick to shooting at such a shallow depth of field (DOF) it is in knowing what aperture will give you what DOF at what distance and how to control it or use it.
Remember, that your image plane is flat and the glass of the lens is perpendicular to it (unless you are shooting a Tilt and Shift lens) and you are focusing with a very limited DOF. So if you are shooting straight on (see fig. 1), then the subjects eyes and maybe their shoulders might be in focus. But, if you tilt the camera down and angle it, the image plane shifts. The eyes and maybe the nose will be in focus, but you pull the image plane away from the body and thus everything drops off and you get a very soft effect (see fig 2). But again, over all there really is no trick. Just a matter if remembering the closer you are to your subject the shallower your DOF will become. So if shooting at 1.2 as close as the lens will let you focus, then there is a chance only the eyelashes and the iris will be in focus. But, even at 1.2 if you back up 10 feet or so, your whole subject will be in focus and your background a soft milky bokeh.