5D mkii AF on moving subjects

[gturner]

I love my 5D mkii, but am getting more frustrated with the poor tracking ability

here are 2 images taken 1 minute apart, both are 100% crops
Both in servo
Both centre point AF activated
Lens - 100-400 L
I am having the same issue with 70-200 F2.8 IS

My theory is that is the IS messing with things, even in mode 2.
Any ideas welcome, including custom function settings.

1. Cat on the wall standing still - perfectly crisp
400mm
ISO - 1250
1/250th @f8


2. my son running past
115mm
ISO 1250
1/500 @5.6

[RichardTaylor]

I use the same lens on a 40D (mostly for sport and birds), which has similar focusing system to the 5DII.

My camera is set up the same as yours.
The only real difference is that I tend not to use IS a lot (I am usually using a mono pod)
The main thing I try to do is to aquire the subject early, with the shutter button partially depressed, to give the autofocus time to lock on.

Also keep in mind that in low light you don't always have a lot of subject contrast for the lens to focus on.

Just talking to other motor sport photographers (including pros), focussing is largest reason they have for technical failures, and it doesn't matter if is is Canon or Nikon shooters.