Quote Originally Posted by Busted Knuckles View Post
Pat, I think you explained quite nicely. Sort of how does the IS system know what is an intentional pan vs. an unwanted shake - assuming you haven't set the IS mode or the lens doesn't have multi modes.
I am not an IS expert, but how I would think it works:
  1. For Canon the IS system senses either 2 axis of rotation (pitch-yaw) or the newer IS systems have 3 axis of rotation (pitch-yaw-roll). Hybrid IS for macro will also sense accelerations in x and y axis (I am not sure about z axis... I would doubt it since the resulting IS lens shift is only in the x-y axis).
  2. Those movements are then translated to an x-y plane shifts to compensate.
  3. If you go to mode 2 for panning, I would think you would ignore the yaw or reduce the sensitivity of the yaw sensor when reporting back yaw position differences (I suspect the later). You may still want some yaw effect for rapid positional changes over time (less amplitude based) and cyclic acceleration (vibration), but ignore the slower rate of change in the yaw rotational position cased by panning. Panning induced movement is going to be relatively lower accelerations. Ideally panning would consist of, starting and stopping accelerations with constant speed - no acceleration - during the pan. So the input for the x-axis motion of the lens would be filtered, or the yaw sensitivity to rate of change would be reduced such that you would get an output to the shift axis only if a given threshold rate of change in the yaw is reached or a cyclic acceleration in the yaw is detected. I would guess it is strictly a reduced sensitivity in the Yaw rate of change because anything else would take to much computing power that I doubt the lens has.
  4. If it doesn't have multi mode IS, then I do not think it does know you are panning, and it will happily mess you up. Try panning a large lens with out mode 2 active, and it does seem to jump more because it is try to compensate for your intentional movement.


Some conjecture on my part because researching the inner thoughts of the Canon engineer that programmed the IS system is not readily available, but that is how I would think it works.

Pat