Maik723 wrote:
Starting shooting kids soccer game using canon 7d Markii with a canon 70-300mm IS on a monopod. Should I keep the IS engaged or turn it off?
Leave IS on.
In fact, with that lens you can leave it on all the time, unless you happen to need to save a little battery power in your camera. And I mean only a little bit of power. In my fifteen years experience and many hundreds of thousands of images shot with numerous Canon IS lenses, it really doesn't use very much juice. I've never tested the difference formally, but feel that during long shoot days, I get almost the same number of shots out of camera and lens with IS on, as with it off or compared to non-IS lenses. At the same time, I have frequently benefited from leaving IS on, been able to get shots that likely wouldn't have been possible without it.
With that lens, when IS isn't needed - such as when camera and lens are locked down solidly on a tripod so that these is absolutely no movement - the lens will automatically turn off IS itself. This is true of most Canon IS lenses. Only a few are known to not do this (28-135, 24-105L, 300/4L, original 100-400L, old 75-300).
I nearly always leave IS on. Even with three of those lenses known to need it turned off on a tripod... mainly because I tend to only use those three lenses handheld or on a monopod... not on a tripod. They're just the size/type of lens that lend themselves to that kind of use.
Two other times you may need or want to turn off IS are when shooting video certain ways and when shooting very precisely framed and composed stills. The reason is that with IS on there can be a slow "image drift" (you'll see it in the viewfinder). This doesn't effect most still shooting at all, but may be an issue with video (fixed position camera, on a tripod) and very carefully and precisely composed still shots (also most likely on a tripod).
Again, in the rare instances where IS becomes a problem, with Canon's in-lens stabilization you'll be able to see it occurring in the viewfinder and can simply turn it off then. It will do no harm to the lens or camera. Worse that can happen is a lost image.
In fact, IS left on will help stabilize the image in the viewfinder, too. And much like it does with binoculars, it can be helpful to the user, even at higher shutter speeds, especially with longer telephoto lenses and when tracking moving subjects.
This all applies only to Canon cameras and lenses with IS... those are what I've been using for about 15 years. I have less personal experience with and no idea about Nikon VR, Tamron VC, Sigma OS, the new Tokina stabilization, or the in-camera stabilization used by Olympus, Pentax and Sony, or others. Canon pioneered image stabilization in SLRs and their lenses. All the others have followed, but their method of stabilization and systems used to do so are different. They have to be.... Canon's are patented, I'm sure. So other manufacturers' stabilization very likely performs somewhat differently than Canon's and may need to be treated differently to get the best out of it.