Hi,
I have the 70-300L IS, and I've shot with it for about a year and noticed that though in general when hand holding relatively steadily the IS starts working pretty fast (< ~1/4s), just a tad slower than other non-telephoto IS lenses I've used. However, when I'm excited or for whatever reason I'm really shaky, it sometimes takes about a full second or even more to completely stabilize. When it is fully stabilized, it works amazingly--I think the IS on this lens works better than on any lens I have used.
I almost always use mode 1. But it appears this also happens in mode 2.
Do you think this is normal? I've messed up many shots due to this delay. For instance, I was shooting friends bungee jumping and I only got about a fraction of a second to lock AF to the target and get the shot, but unfortunately my motor skills suck and I shake a ton while doing this. I try to give the IS as much time as I can to spin up, but it just wasn't enough most of the time.
So, I know part of this is probably lack of skill, but ignoring that part, is the IS supposed to take that long when you're shaking a lot? Again, it works pretty fast when just shaking a bit--it's only a problem when I shake a lot.
Thanks 
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