The Al Servo setting on the EOS Canon Professional Cameras are normally fast enough to keep up with a moving subject. However, in very cold conditions you may find the AF response slows down a little and you have trouble tracking the subject. If this happens, try to keep the camera warm – if you are visiting a particularly cold country or are shooting within the arctic circle, ensuring the camera is covered and as warm as possible will allow the best AF tracking possible. As an aside, it will also help extend battery life.
News Source: Canon Professional Services
By: Martin Allred