40D AF settings for moving candid shots?

I was out with some friends for a nice walk in the country side and took along my 40D and 70-200 f/2.8 IS to shoot some candids. There were three children running around, certainly making the most photogenic of subjects, but I was struggling somewhat figuring out which AF point to use. I was in Av mode with aperture at f/4 for a nice creamy background but a little leeway on DOF. Of course, focusing on the face (eye) is paramount (or is it?) so I was really struggling to keep up with the pace of motion as they ran first left, then right, then towards me.

Obviously I wanted a nice composition, with space in front of them to run into, and I just felt that the whole AF point selection process was too unwieldy, and kind of hit and miss with that tiddly, imprecise, joystick, that takes 2-3 attempts to get the right AF point lit. Basically, by the time I had the camera set up to focus and compose correctly the moment was gone. What on earth is the correct approach - use centre point and focus on their bellies/chest and hope for the best? - only photograph them moving right to left or left to right, but not both? - get a camera with clusters of AF points in the area of interest (face)? - use top AF point only and sod the composition? - enable all AF points and acquire with the centre point and then let the camera track whatever it felt like - maybe the closest hand, maybe the farthest hand, who knows?

I was using AI Servo and the AF-On button to focus but that damned AF point never seemed to be where I wanted it to be. I guess the challenge is a bit like sports photography (not that I do any), with a 400mm f/2.8, but on a smaller scale. What could I have done to make my life easier?

If it were me I'd have probably just manually focused.

I shoot birds a lot, many of them waders like stilts, egrets, avocets etc. When they're on the move I usually MF in order to get the framing that I want. If I use AI servo on the center point they're smack dab in the middle which is wnere I don't want them.

I use AF occasionally to get in the neighborhood and then MF. It may not work for everyone but it can work if you pracitce a little. It seems to me that people expect AF to work flawlessly all the time and that's just not the case.

Of course having a better AF camera such as the 1D III can help.

At, for example, 200mm, f/4 and 30' subject distance the DOF is +/- 6", which leaves little room for error when manually focusing through a cropped viewfinder on a moving target.

It's not that the AF does not work. It's more that in a dynamic environment, there seems to be no easy way to have the camera set up so that it can respond quickly to the changing scene. Maybe I just need to practice my joystick manouevres more, because so often, when I want a diagonal AFP I end up with one of the outer points. The joystick is just too fiddly to operate quickly and reliably. What I would like is a cluster of AFPs that can be targeted around the frame - e.g. a cluster near the top of the frame, whichever way I orient the frame. This would be like using all AFPs but in a targeted group in one part of the frame, rather than across the whole frame.

Single FPs are too restrictive and demand precision aiming, which might not suit the compositional needs. If you switch from portrait to landscape and back again, ideally you want the relative position of the FP to stay where it was - e.g. if it was top right diagonal and you wanted to quickly reorientate the camera you still want the top right diagonal to remain the chosen AFP. You don't suddenly want it to become the top left or bottom right, just because you swivelled the camera. But the AFP does move with the camera and so you need to be able to quickly reselect the active AFP - but the joystick is error prone, when used in a hurry, and you have to move your thumb from the AF-On button and back again, so you fumble around and miss the shot.

Now, obviously the 40D does not have such a feature, to (a) focus around a cluster of AFPs; or (b) dynamically relocate the active AFP when the camera is reorientated, and I don't know whether any camera does, so, other than manual AF, what AF setup would people normally use for such a rapidly changing environment?

To take this further, I was watching a reality TV show called "The Shot" where 10 fashion photographer candidates are pitched together to battle it out for the $100,000 prize etc.. Looking at their fast paced photography I am really curious to know how they would have been focusing, because they sure weren't taking the slow and deliberate steps that I do, to carefully place the AFP over the eyeball, focus, reframe and then shoot. They were just blatting away without a care in the world. Maybe they were at f/11 or even f/16 and didn't need to take much care, in the studio, but I feel my focusing technique is so deliberate and ponderous that I am missing out on "the moment".

Any more ideas?

Correct me if I am wrong but I thought that when the camera is in AI Servo mode it automatically assigns the focus points and moves to whichever is closest dependent on the subject. This is why it doesn't flash a focus point when the shutter is half pressed.

Skids wrote in post #5781217
Correct me if I am wrong but I thought that when the camera is in AI Servo mode it automatically assigns the focus points and moves to whichever is closest dependent on the subject. This is why it doesn't flash a focus point when the shutter is half pressed.

Only if All focusing points were selected.
In that case, it starts with the center focusing points and as the subject moves across the frame, it is picked up but other FPs.

It doesn't flash in AI Servo because focus is all the time adjusted and re-adjusted, regardless of how many AF points were selected.

In AI Servo and all points enabled you must first acquire the target with the centre point. Once focus has locked with the centre point, the camera will track the subject if it moves away from the centre point and another focus point picks it up. I think this method assumes a smallish target that doesn't cover several FPs at once. I'm really not sure how well that approach will work when your subject is a three dimensional child with swinging arms, one of which will be a lot closer than the other. If the camera picks up the closer arm/hand you've wasted half you DOF in the thin air in front of the subject. This is why I want to keep focus on the face/eye, while still achieving a pleasing composition. Maybe the answer is to close down the aperture and gain a deeper DOF, or zoom out a bit and focus with the centre point only and crop the resulting image to achieve the desired composition.

I'm interested to know how others would approach such a challenge. I expect I'm using completely the wrong approach - but what should I do?

Then you are hereby corrected. Your description fits what happens if you enable all AF points in Servo AF, but if you enable only one point, then only that point will be used.

To the OP, you can try setting the rear wheel as immediate selector of AF points, instead of the joystick. You may find it more precise, even if you have to cycle through the selections.
Then you can't set EC directly, but you still can indirectly, if you press the AF selection button and use the front wheel.

tdodd wrote in post #5781234
In AI Servo and all points enabled you must first acquire the target with the centre point. Once focus has locked with the centre point, the camera will track the subject if it moves away from the centre point and another focus point picks it up. I think this method assumes a smallish target that doesn't cover several FPs at once. I'm really not sure how well that approach will work when your subject is a three dimensional child with swinging arms, one of which will be a lot closer than the other. If the camera picks up the closer arm/hand you've wasted half you DOF in the thin air in front of the subject. This is why I want to keep focus on the face/eye, while still achieving a pleasing composition. Maybe the answer is to close down the aperture and gain a deeper DOF, or zoom out a bit and focus with the centre point only and crop the resulting image to achieve the desired composition.

I'm interested to know how others would approach such a challenge. I expect I'm using completely the wrong approach - but what should I do?

You are right about most of the things you wrote except for "the smallish target....".

How it works that, in AI Servo, with all points selected is..... it acquires initial focus with the center point. As long as the focus point is on the target AND another focus point is on the target, it will hand off focus to the second point if the first point goes "off target". You must always maintain at least 2 focus points on the target if you widh the system to hand off to another point (the other point being on the target at that instant".

It works quite well, actually.

So, the target can't be "smallish". It must be large enough to be covered by 2 focus points, initially the center point.

Generally, in action, the best policy is to try and lock on with the center point on the face, or if it is a small target on the biggest area you can keep on target. Let the composition fall as it may. You can always use zoom to incorporate more or less of the scene. Crop later to get a better composition if needed. I think you will drive yourself crazy trying to switch autofocus points when the action is fast. Better to get the shot than miss it worrying about the rule of thirds!

Switching points to match the action requires a lot of practice, but it can be done.

Set the camera up so AF is on the focus button, and AE is on the shutter. Select the center only focus point. Put the center on your subject, tap the AF button, then slide over to recompose and press the shutter. With practice, this all takes well less than half a second And I use this to method to shoot action sports.

Hmmm.... Plenty of options there. I don't get the chance to practice this kind of photography much but I will try experimenting. Thanks for the suggestions.

Hermeto wrote in post #5781231
Only if All focusing points were selected.
In that case, it starts with the center focusing points and as the subject moves across the frame, it is picked up but other FPs.

It doesn't flash in AI Servo because focus is all the time adjusted and re-adjusted, regardless of how many AF points were selected.

Well I have learn't something new today

I thought once it was switched to AI Servo it automatically enables all AF points so that it can track the subject.

bsmotril wrote in post #5786420
Set the camera up so AF is on the focus button, and AE is on the shutter. Select the center only focus point. Put the center on your subject, tap the AF button, then slide over to recompose and press the shutter. With practice, this all takes well less than half a second And I use this to method to shoot action sports.

Curious how that would be effective on a moving target (action sports).

bohdank wrote in post #5788278
Curious how that would be effective on a moving target (action sports).

If you don't mind cropping, to get the composition you want, then it makes a lot of sense. The centre point is normally the most sensitive/accurate, and often, especially in team sport, you will need to pick your target precisely from in between the flailing mass of bodies all around.

If you go with all points then you're at the mercy of what the camera ends up tracking, even if you first lock correctly with the centre point. If you go with a non-centre point then you limit your framing flexibility. If the action heads off in the wrong direction you'll be caught with the play off the edge of your frame.

So, AF with the centre point only and leave a little slack in the composition to crop as you would like. I don't like the idea of having to crop at all, but better to chop off a few surplus pixels than have a crap composition or focus on the wrong thing.

I think I'll try the centre point technique, with looser framing, myself.