Does IS affect AI Servo?

Hey guys,

I bought a 7D a while back and had many many issues with it. I had to send it to canon 2 times. I got it back for the 2nd time today and so far it is performing much much better. Before the focus was all over the place (even on static subjects using spot focusing)

Anyway, I am new to using long lenses and doing BIF...so I am starting slow.

Today I took my dog out and put my 100-400L on the 7D and threw a tennis ball for him to retrieve. I used the following settings:
1/800 f5.6 at 400mm
AI Servo
IS on
C.Fn-III-1 Servo Tracking sensitivity : one step to the right (fast)
C.Fn-III-2 AI Servo 1st/2nd image priority : 0-AF priority/Tracking Priority
C.Fn III-4 Lens Drive when AF impossible : 1-OFF

I took pictures of my dog running toward me with the ball. Each time I had it focus directly on his face. About 85% of the images tend to be back focused. Could it be that this is caused from the IS taking to long to kick in or is the tracking not keeping up with my dog? What I mean by this is that it focuses, takes the picture and by the time the picture is taken his head is out of focus because he became closer causing it to focus behind him. Is that the problem, or does the IS not work that way?

Any help would be greatly appreciated.

The floating lens element used in stabilizer assembly is seperate from the focus elements so IS should not directly affect AF. Is does need time to settle (about a second ) the first time it is engaged but it should not cause back focus issue that you describe. Try some static AF tests to see if the back focus issue is consistent, if so try the microadjusf feature to bring the focus plane closer. Keep in mind that you can do this for one focal lengh only.

I just got off the phone with CPS and explained the situation to them. He pretty much told me the same thing you mentioned Arash...but he also said that it could be that the back in of the dog is coming into the range while the dog goes up and down in his stride. So he told me to set C.Fn-III-1 Servo Tracking sensitivity to -1. I am going to give that a shot and also go to the local park and track some gulls to see if it looks good.

If you're interested, have a look at my 7D setup guide. It may help.

I read your article and I have most of the same settings as you. Either way its a great article and I appreciate you putting something like this out for all to read!

shane

C.Fn-III-1 Servo Tracking sensitivity : one step to the right (fast)

most people set it to SLOW

In the scenario of the dog moving and the focus shifting to the rear of the dog (back focus) the slow setting would tend to lessen the focus shifting as quickly.

I find that setting the AF tracking sensitivity to slow is best. The camera is a lot more stable producing many more keepers.