An endless topic of conversation among Canon 1D Mk III owners is how the Auto Focus performs in AI Servo mode, in which the AF tracks a moving subject. This is one of the Mk III's top features, yet it had problems in its early introductory phase which were supposedly resolved with a combination of hardware and software fixes.

I took several seconds of the train approaching so that may be the best (and longest) sequence to really see the effectiveness of the tracking AF, then two to three seconds as the train departed...
This is an issue that concerns those of us who shoot any active subjects, whether sports or wildlife. My problem is that there are skills to be learned here, sometimes handholding a big lens/camera, often tracking a moving something, and when I'm out chasing wildlife I'm often acting as erratic as the animals myself so it's hard to do controlled testing.

So, as I was relaxing at one of my favorite getaways and photography spots, aka "Critter Lake" a few minutes from my home, I heard the horn of an oncomong train and got the inspiration to go up the bank with my 1D with a 300mm f/2.8 IS lens, mounted on a monopod, and try tracking the train as it came and went.

And so I did, with the camera in AI Servo AF, center point focus, and using the back AF-On button to put in AI Servo mode, the shutter button kept down for continuous shooting (at 3 frames per second).

This kind of thing is new to me (panning like this) and I was using a monopod rather than a tripod, so I allow for the possibility of me messing up some shots. All in all, there were several out of the twenty or so shots that were less than sharply focused, but the majority were quite sharp when viewed blown up to 100%.

See for yourself! I'm posting the whole sequence as "100% crops" with a beginning, middle and end full-size shot inserted so you can compare fairly then ones that turned out soft with the ones that turned out sharp. Have fun!

***WARNING! VIEWING ALL THESE SHOTS MAY BE TEDIOUS, SINCE THERE WERE SEVERAL TAKEN A SECOND!***
Conclusion? Well, first, I need to hone my technique. Between lack of experience and changing light, I suspect that I'm to blame for soft shots. Some more practice and testing is in order! In the meantime, the majority of these shots are "keepers", which is good news!