What focus point and mode when shooting portraits wide open

Ok so I have always used single spot focus point on the eyes in one shot mode when hand holding the camera.
When using 85L at 1.2-2.0 or 135L at 2.0 we all know dof is extremely shallow.
So is it better to shoot in AI Servo and single focus point instead of One shot and single spot focus? Models have a tendency to move a little and not uncommon when shooting hand held for the camera to move slightly too.

Ok I just tested this at 1/500 f/1.2 using AI servo and single and spot focus points with the 85 1.2L II. And my result showed that the eye was in sharp focus exactly 50% of the time regardless. Which wasnt better than one shot and single spot focus. The AF is slow on the 85 1.2 so response time in AI servo is slow. I will try this with the 135

Ok I just tried this with the 135L 2.0
In AI servo with single focus point not spot 95% of the time the eye was in sharp focus
In AI servo with spot single focus point the focus was only 50% sharp focus on eye
I would think the faster focusing response of the 135L accounted for this high rate of success compared to the 85L. So for me I will shoot 85L in one shot-single point and the 135 in AI servo and single point focus. I am surprised the spot single focus point didnt fare better with accurate focus on the eye

gqllc007 wrote in post #17696822
Ok I just tried this with the 135L 2.0
In AI servo with single focus point not spot 95% of the time the eye was in sharp focus
In AI servo with spot single focus point the focus was only 50% sharp focus on eye
I would think the faster focusing response of the 135L accounted for this high rate of success compared to the 85L. So for me I will shoot 85L in one shot-single point and the 135 in AI servo and single point focus. I am surprised the spot single focus point didnt fare better with accurate focus on the eye

You seem to be thinking that the spot AF is there for better accuracy, it isn't. The spot AF is less accurate than the regular AF point, as it has less to work with and may have trouble finding a good line of contrast to lock on to. It isn't there to be a more accurate focus point, it is for when you are trying to shoot through tight gaps in something closer which may be focused on instead with the larger AF point (such as twigs near a bird in a tree, or a chain link fence between you and your subject). For portrait use, where no such obstructions are present, you should be using a regular AF point and aligning it with a good line of contrast for the best results. That is what your test showed.

That clarifies what focus point to use but not what mode to use AI servo or One shot?

I use spot AF for portraits, I use it to lock onto the eyes. It is more accurate if your subject has a good point of contrast. I use ai servo just in case I or the subjects move. Otherwise one shot if dof covers the entire body of the subject. Spot AF is good for picking out that one person in a group shot as well, that will get the entire group into focus while trying to blur the background, without thanking the aperture too small.

I use one shot and I've never had the issue of a model moving.

maverick75 wrote in post #17697556
I use one shot and I've never had the issue of a model moving.

Time for younger models?

agedbriar wrote in post #17698325
Time for younger models?

Like toddlers
Or pet photography

TeamSpeed wrote in post #17697551
I use spot AF for portraits, I use it to lock onto the eyes. It is more accurate if your subject has a good point of contrast. I use ai servo just in case I or the subjects move. Otherwise one shot if dof covers the entire body of the subject. Spot AF is good for picking out that one person in a group shot as well, that will get the entire group into focus while trying to blur the background, without thanking the aperture too small.

maverick75 wrote in post #17697556
I use one shot and I've never had the issue of a model moving.

Do you guys use BBF or let the shutter meter/focus when you use spot AF? Been playing with a mix -- have been using BBF for years, but have started doing some portraits and am finding slight focus issues with BBF and one shot, not so with BBF and AI Servo -- so considering changes in my technique, but have been using center point focus for all of this --

But it also depends on your camera. My 6d is good with the center point but my 5d3 is way better if I select another "hot spot" out of the gamut

In my experience, one shot focus is more accurate and works in lower light than servo focus.

Some people suggest that servo will be good if the photographer or the model moves just a little, but in my understanding, Canon's servo focus is designed for and expects much more significant movement that a tiny 1cm sway by your model. In my experience servo doesn't do any kind of magic in tracking such a possible tiny sway. As far as the camera is concerned, a model 4 meters away that is swaying back and forth 1cm is going to be seen as stationary by the camera. It will probably not update the focus distance and move the lens.

Best bet on a stationary model is to focus with one shot, and snap the shutter immediately after attaining focus, before you or the model can move.

JeffreyG wrote in post #17703232
In my experience, one shot focus is more accurate and works in lower light than servo focus.

Some people suggest that servo will be good if the photographer or the model moves just a little, but in my understanding, Canon's servo focus is designed for and expects much more significant movement that a tiny 1cm sway by your model. In my experience servo doesn't do any kind of magic in tracking such a possible tiny sway. As far as the camera is concerned, a model 4 meters away that is swaying back and forth 1cm is going to be seen as stationary by the camera. It will probably not update the focus distance and move the lens.

Best bet on a stationary model is to focus with one shot, and snap the shutter immediately after attaining focus, before you or the model can move.

The only thing with this is that when I do portraiture, there are 2 moving subjects, myself and the person/persons being shot. And if there are kids, that introduces a whole new level of complexity, as they are just little bundles of raw energy, and sitting still isn't in their vocabulary.

Now with purely a studio set up with tripod and very controllable subjects, I would definitely use One Shot.

Not only do I need AI Servo for kids portraits, I even have Case 3 selected, for high tracking speed. Case 1 often wasn't fast enough on my 5D3.

Besides kids moving even when they mean to "pose", it's also me, struggling to capture the moment.

I tested AI Servo on static subject with the quite sensitive Moire pattern and Siemens star methods and in decent light the difference in favor of One Shot AF was barely perceptible, practically lost wthin the normal AF variability.