Canon AF Tracking Surprise

I wasn't sure where exactly to stick this, so I figured to put it here. My oldest two girls play softball and I usually shoot the team. I'll often shoot pitchers head on at some point, I set up just far enough off line to get around the catcher and umpire.

So today my 5D3 + 70-200/2.8 IS II surprised me. I was shooting with no AF expansion. Right as the pitcher release the ball, the ball itself was in the AF point. The camera somehow calculated the speed and the servo stayed with the ball through the burst, even as the ball left the active AF point.

Nothing much else to comment on here, I guess I was just surprised how well it did from such a short amount of time seeing the ball speed. This pitcher throws at just about 60 mph.

Here are the three shots, in reverse order:

Last shot

Single AF point? And were the shots cropped?

The last one would go well in the "frozen ball" thread

Archibald wrote in post #18348775
Single AF point? And were the shots cropped?

Yeah, single AF (center point) and I just hit the image with a centered 4x5 crop to discard the ends. The ball was directly at the AF point as it comes from her hand, but then is gone from the point. I believe the AF tracking selections I had allowed the AF system to stick with the ball despite it leaving the active AF point.

JeffreyG wrote in post #18349520
Yeah, single AF (center point) and I just hit the image with a centered 4x5 crop to discard the ends. The ball was directly at the AF point as it comes from her hand, but then is gone from the point. I believe the AF tracking selections I had allowed the AF system to stick with the ball despite it leaving the active AF point.

Well, that is impressive, but I don't understand it! How can the AF system see that far past the selected AF point? Yet I've seen similar things when tracking birds in flight. There are things we don't understand about Canon AF.

The tacking birds is easy. I've done it lots of times. Use a low Tracking Sensitivity (TS) setting. At -2 you get about 1 second before the system drops focus on your primary subject and starts to look for something else to focus on. If the subject is in focus and it veers off the AF point, at 10 FPS you can get 10 in focus shots with the AF point no where near the subject

However I have always done this tracking birds moving left, right, up and down so this new to me. Interesting that it works front to back just as good if that is what actually happened. I'd have no other explanation as only one AF point was engaged. IMO expansion would not have made much difference. It even changed the DOF. I always assumed that only worked on a flat plane.

There were conversations about AF not locking while in AI Servo on another thread. I mentioned that maybe it does lock on a subject and tracks it but will release and lock on something when AF points find a new subject. The TS setting is the release speed.