I tried Soccer for the first time this weekend, and I killed a huge number of photons with out of focus shots; since I never like to torture innocent photons, looking for a better understanding.
Here is what happened repeatedly.
In AF-C, 9 or 21 (tried both) point mode, I would start a burst, say someone making a shot. I would try to track the action during the burst. It would look great in a brief check of the LCD.
Back home what I found is the first few images were in focus, but by maybe #3-#5 focus would shift to something else -- the net in the background, a fence, usually something more distant, occasionally something close.
I fired up ViewNX, and what I saw there was usually good tracking, then 1-2 frames with no focus point, then the focus point on something completely different. Below is a series shown in ViewNX. The top three are in great focus (I know you can't tell), the bottom three are not; by the last one the focus point is on the net.
This particular series was in 9 point. My first thought was I was outside of the 9, but if you look carefully the image directly above the last shows the focus point roughly where the guy's head and/or goalie's foot is.
How does tracking work between shots? Does it re-center to the selected focus point for each shot and track for that fraction of a second? Or does it start where the last focus point was?
I'm thinking 9 is too small, and maybe 21 was as well?
How does A3 (Focus tracking with lock on) work, is that just while focusing or is that also between shots? I was on "3" (Normal) the whole time. There's no real metric provided, not sure what "long" and "short" mean, and experimenting is somewhat hard (to find a predictable target).