I remember another thread where we discussed this but I can not find it. It was April or May 2010.


I asked Canon some specific questions about this. Here is the answer:


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Canon does not quote the sampling frequency for its Image Stabilizer mechanisms. Also, Canon does not recommend users to avoid using IS at fast shutter speeds. The visual effects of IS in captured images diminish as the shutter speed increases over 1/focal length, but the use of IS for moving subjects in these conditions can be beneficial because it presents a steadier image to the camera's AF detection mechanism.






We can can confirm that it takes about a half second for Image Stabilization to become operational with most IS-equipped EF and EF-S lenses. Even so, Image Stabilization is a useful tool for many photographic applications including bird photography at high shutter speeds. However, like any other tool, it requires good technique on the part of the user for best results. Additionally, some photographers may prefer to shut it off at least occasionally depending on their shooting style. Bottom line, it makes no sense to declare that IS is either "all good" or "all bad" when it comes to bird photography. Use it when you need it, and for best results, let it come up to speed before you release the shutter.






Incidentally, it is not necessarily true that IS must be shut off and re-engaged when AF is shut off and re-engaged. IS can operate independently from AF through Custom Function control. On current EOS models, for instance, Custom Function IV-1-2 allows IS to be operated by the shutter release and AF to be operated by the AF-ON button. Using this method, IS remains active for several seconds after pressing the shutter button halfway while disengaging and then reengaging AF.






Canon IS and Nikon VR do not share the same operational principles, so this question cannot be answered as written. The IS specifications mentioned in "EF Lens Work III" refer to the degree of lens movement, not the sampling frequency of the gyro sensors.