How would you focus in this situation

Hi,

A bit of a challenging low light situation that I shoot every Easter Vigil. Here is a shot I took with a rented 5D2 and a 50mm 1.2, shot at 1/160, f 1.8 and 2000 ISO:

It's just like auto racing back when I had only manual focus lenses. You get to a corner where the car is going to be turning right towards you, you focus on that spot on the track, and you fire just as they hit the mark.

A little harder here, but the same concept. And I would shoot at 2.8 at least. Even narrower if you can use flash.

I agree with the above. At least f/2.8, so that my initial focus lock provides a focal plane that stays relevant throughout the movement. I'd be at 1600 ISO, 1/200 and I'd bounce a light camera left (off a wall, ceiling, whatever). If flash is out of the question I'd lean on that ISO--with the 5diii you should be fine.

Interesting, when I asked this question I was mainly wondering which focus point to use (single point, spot, maybe group single point) with AI Servo, and I got a much different response. I've tended to shoot multiple positions from the subject sitting upright, all the way down and all the way up. And they are immersed three times, so I end up with like 10 images. So if I did use a predetermined focus point I'd just be catching them as they are getting wet, or just coming up..... fewer shots but potentially fewer OOF shots.

I'm surprised no one thinks that the AF could follow the subject effectively in AiServo.

I am going to adjust some LED track lighting to the area from up high, but no flash is allowed so that's all I can do.

One last question: how do you feel about using Auto ISO in this situation, i.e. manual exposure at 1/200, f 2.8, then set the ISO to Auto? I'm thinking I'm going to be 3200 or higher.....

Thanks!

Except for sports, I don't use AI Servo. I've never trusted it, though that's a legacy from older less sophisticated cameras than the 5D3. I understand the AI Servo on the 5D3 to be excellent and it's probably a better alternative. I just don't tend to think and work that way.

I wouldn't use AI Servo mainly because the depth of field of the action zone here (especially if you're situated from the perspective you are here (and I think that's a decent perspective) isn't that large: >= F/2.8 should do it.

There is no (see exception to follow) purpose to auto iso here because you're shooting in a situation in which your ambient light is fixed, unchanging. You should be in manual mode. Now if you're quickly moving between this area and some other area (ie. reactions) I can appreciate the desire for some auto exposure (like auto ISO or P mode); but I'd be in M.

50L @1.2 isn't exactly sharp. I would stop that down or use an entirely different lens.
With the 5D3, you should be able to boost the ISO a little more, but ISO2000 is nothing for either the 5D2 or 5D3. Don't be afraid to boost it more. ISO4000-ISO6400.

Peacefield wrote in post #16840363
Except for sports, I don't use AI Servo. I've never trusted it, though that's a legacy from older less sophisticated cameras than the 5D3. I understand the AI Servo on the 5D3 to be excellent and it's probably a better alternative. I just don't tend to think and work that way.

I'm still learning to trust it AIServo on the 5D3 but keep finding it works very well. The problem, for me at least, seems to be that it works so smoothly I'm not sure it is working until the shoot is done and the big work station screen shows tack sharp images.

jmikolich is spot on. Stop down to 2.8 at least so you're sure you're going to get the kid in the DOF, pre-focus and then shoot in manual, shutter at least 1/200th so you don't get motion blur, and ISO 3200 on the Mark 3 will work fine.