@jrhoffman75 wrote:
http://www.learn.usa.canon.com/resources/blogs/2014/20140225_winston_IS_blog.shtml
"Another forgotten I.S. advantage
Image Stabilization isn’t just a benefit at slow shutter speeds when hand-holding, however. It can actually make your AI Servo AF better — even at the fastest shutter speeds.
I’ll switch gears and look back at another shot taken with an EF Extender, in this case, using the superb EF 200mm f/2.0L IS lens and an EF 1.4x III Extender at a hockey game. Effectively, this hand-held combination is a 280mm f/2.8 lens, shot wide-open in available light. In action situations, Image Stabilization provides a much more stable view in the finder, even when rapidly moving the camera to follow an erratically moving subject. But beyond that — and many sports photographers don’t think of this — if I.S. is active, the autofocus sensor gets the same stable, clear view of the subject that you would through the viewfinder. Whether working hand-held, as I was in this shot, or from a monopod, the AF system gets a better look at the subject and has an advantage in reading detail and reacting instantly to it during a high-speed, continuous shooting sequence. The benefit? Even greater likelihood of consistently sharp frames, throughout a sequence."
Great point you have made. But in our action case, I think you're assuming that the AF system gets a better look at the subject. I'd say not when it gets confused. We are saying that when you're panning ̣(meaning deliberate movement), in mode 1 and 3, the IS is trying to cancel that panning movement to deleterious effect. Even in mode 2...who can pan perfectly laterally anyways. Canon does a great job compared to Tamron and Sigma but when you pan after a bird, you're better off without IS. Tamron says it in bold print to turn IS off when you do this. On the Tamron 150-600mm, Tamron came out with a firmware to automatically turn off IS when it detects panning. I suspect Canon also does this without telling us.
