Now this question is asked a LOT and I really mean A LOT.
“Frank why do you move your camera up and down?”
“Which focus point should I use?”
Both questions actually boils down to the same answer.
I grew up with analogue photography, meaning focussing manually with a great (and sometimes not so great) focus screen, often this were the screens where you would see the image opaque in the center when it was in focus, plus/or a circle that made the image broken up or complete when out/in focus. These focus “helpers” where always in the middle of the frame, now did this mean that your subject was always in the middle…. no of course not, you would focus, recompose and shoot.
Now we enter the digital age and the DSLRs have 19-36-100+ focus points, in essence one could place the focus point on whatever location one wants and have optimal focus… well yes and no. The first thing you have to realize is that focus is important in a shot, but I strongly believe that composition is even more important, and most of all playing with composition. Now some people will now go like “huh, what do you mean with this Frank?” so let me explain.
A lot of people will choose a focus point which lines up with the eyes of the model and start shooting, well that sounds logical but…… for me it isn’t, in fact it will limit my creativity or workflow a lot. If I would use this technique I would change my focus points almost constantly, meaning I would make my composition, use the selector to select the focus point and press to take the shot, and probably recompose a bit before I press the shutter because the chance my composition is spot on with the available focus point is very small.
So if I don’t select my focus point how do I focus?
Well very simple, I will always use the center focus point, get the focus correct and hold the focus (half press) now recompose and shoot, this is a VERY quick movement, one could say that theoretically the focus will shift, and yeah that is a chance, especially when you use a lot of movement in your recomposing (eyes on the edge for example), however in practice I have to say that it never really happens to be a problem, in fact when you shoot Medium Format cameras like the Phase One/Mamiya DF there is only one focus point, yep in the center (well actually there are more but they are in my opinion useless because they are very close to the center). So when shooting with Medium Format where the focus is much more important than with a DSLR there is no choice and as you all can see the images I take with these cameras are razor sharp in the areas I want them to be sharp.
So I really don’t worry too much about it, and I think you also shouldn’t. I would rather feel free to play with my composition than to be stuck with a focus point I choose and have to worry about changing that focus point over and over again.
So what do you do when shooting wide open with 1.2?
Well….You are right, when shooting with such shallow DOF there is a chance that whatever you do will shift the focus, but that also can happen when you don’t recompose, this is actually where I love focus peaking, on the Sony I always have this enabled in the EVF (Electronic View Finder) but with other brands you could use your liveview for this. This is actually the only way to make 100% sure (well there is no 100%) that you get the focus correct. And if you really want you can of course select your focus points when shooting with these lenses, but overall I strongly think that the effort and limitations you have to life with doesn’t make any sense. I shoot a lot of images and from all the images taken during a shoot I hardly have any focussing problems, but I also think it’s a matter of getting used to the technique.