Great shots, Northstar! Having spent countless hours trying capture figure skating, I can appreciate everything that went into these shots, particularly the timing. Was this with your 1Dx or 5D3?
Back to the IS question. When to use IS is still a hotly debated topic. I suspect the real answer is “it depends.” It may depend on the focal length, the body (FF or crop), the subject matter, and/or the manufacturer.
In this thread, we are considering a T2i with the EF 70-200 f2.8L USM IS II.
First, I still contend that 1/500 isn't fast enough to eliminate camera blur while shooting hand held action shots with a 200 mm lens on a crop body, which magnifies image movement over that of a FF body.
Second, Nikon's VR and Canon's IS are different systems with different algorithms
. Canon pioneered lens-based image stabilization in 1995. Nikon played catch-up in 2000. Canon starts stabilizing the image when the shutter is pressed half-way, before focus is locked. Nikon initiates when the shutter button is pressed half-way, but does a “recenter” action just before the shutter is tripped. Nikon uses a sampling rate of 1000Hz (1/1000 sec) which means it's only accurate to half that speed, or 1/500 sec. This supports Scott Kelby's advice to turn off VR when shooting at or above 1/500. It also supports the notion that VR can get in the way of rapid burst sports bodies.
However, Kelby was talking about Nikon's VR, not Canon's IS
[Here's more detail on Nikon's VR system http://www.bythom.com/nikon-vr.htm
Canon hasn't published it's sampling frequency and Canon officially states that it's IS system is designed to aid the focus system even at high speeds. When asked about using IS for photographing skiing with high shutter speeds, Canon's Chuck Westfall, says leave it on http://digitaljournalist.org/issue1002/tech-tips.html
(see 8th question).
The Digital Picture's forum includes a more detailed response from Canon on this subject [from http://community.the-digital-picture.com/showthread.php?t=5279
]: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.
Back to the question of IS on for hockey with a T2i. The T2i FPS rate is 3.7 and likely too slow for image stabilization to impede it's rate (if Canon's IS would do so). This leaves us with two questions. Is there a shutter speed limit with Canon's IS such that faster speeds do nothing to further steady the image? Is there a shutter speed and/or frame rate that will “fight” with Canon's IS system and impede focus lock?
Sadly, Canon's official documentation and lens user manuals do not answer either of these questions. I have found nothing definitive from Canon or specifically about Canon's IS system that supports the notion that it's IS is not effective beyond 1/500 second or will degrade focus lock at higher speeds.
While I still think it's best to leave IS on with high shutter speeds – that it won't hurt and may help – I'd still like a more definitive answer from Canon. With a 70-200 on a T2i at 1/500, I still say leave it on (in Mode 2). At 1/1000, it may not matter. In between, good question.