AI Servo with 1DMKIIN

The other day I was shooting a triathlon and was taking some bike shots and was in AI Servo mode. I took one shot and filled the frame and then zoomed in to get a tight crop and about 50% of the time just when I pushed the shutter the image went out of focus. This was driving me crazy and wonder what you pros have your AI Servo mode set to?

Any help or suggestions would be much appreciated.

Dave

Your lens might be parafocal, requiring refocus when zooming in or out.

did you use CnFn 4/1? It seperates AF to the "*" button and the shutter button only does AE and shutter release, so once you have good focus, then you don't nee to touch it again. If it's in default setting, then pressing down on the shutter will activate the AF everytime.

sounds like your letting the presure off the shutter button as you zoom then its trying to snap back in focus as you press it. just a thought.
Rob.

That's the wrong way up. A parfocal lens doesn't need refocussing when you zoom. There's a partial list of parfocal Canon EF lenses here.


David

What were you zooming in and focusing in on? You have to remember that your "target" has to have some type of contrast for the focusing to work. For example, a solidly colored object is not going to focus very well because it totally lacks contrast.

* button might do the trick...

Sorry folks for not explaining more.

I do have the focus set on * and have it pressed all the time while I'm shooting. I think some of the issues is with the contrast issue but not completly sure. I have the Sigma 70-200 2.8. I also use the center focus point and normally focus on the trunk of the body to place the head in the upper part of the frame. Should I be using a different focus point or more of them?

Dave

It depends but sometimes at f2.8 focusing on body can easily produce photos where head is already out of focus. Otherwise you should be able to shoot triathlon (even bike section) without any problems even with Sigma. I was shooting quite lot with this Sigma before, and I was shooting much faster sports then running or cycling is.
It also might be quite possible to have problems because of low contrast. White t-shirt doesn't make much of a contrast for af to lock down.
Otherwise post this "out of focus" photo and maybe we can help some more when we will see sample.

pyterps - You didn't mention lens but I sometimes experience same situation in my horse events. At times the subject is moving in a wide arc where they are (lets say) moving from right to left and away from you slightly at the beginning and then reaching the apex (at a 90° angle) then coming around to eventually draw nearer and facing you in a head-on view.
My 70/200 will hunt a bit if I get off my target even a little. Ideal point of focus is mid-calf to knee. Light horse and white jodphurs is tricky as are black chaps and dark horse.
Just one more thing that makes sports eventing so darned challenging. Especially if you have that big white tube way out there.

Hmmm, not sure, I'd think zooming in shouldn't cause it to attempt to refocus.