2. Use of Canon's Lens Image Stabilization (IS) Function and a Tripod
My reason for looking into this was due to a gradual movement of the image when using Canon IS lenses with the IS switched "on" and when the tripod and lens were absolutely still. If I was using a slow shutter speed my images would then be blurred. I found on these occasions when you have a rock solid, still, camera/lens/tripod or bean bag set-up It’s best to switch your IS “off”. Which I later noticed was as per the manual :-). However, to simply turn off your IS every time you use a tripod, particularly with long lenses, on a windy day or in an awkward position, does not make full use of your IS functionality. I have found it best to be aware of this IS induced motion and when it occurs, turn the IS “off”, and leave it “on” at all other times (even when using a tripod). If you are using a monopod it nearly always pays to keep your IS turned "on" unless you have somehow wedged it against a solid object for stability.
I have noticed this IS motion issue is most prominent with my 100-400mm L IS and 300mm F4 L IS and hardly ever occurs on my 500mm F4.
I then decided to find out what others had to say on this. It turns out that my practical experience above has proved correct. There were also some other useful lessons:
1. Canon’s lenses have a range of IS generations which cope better or worse when used with tripods.
2. Canon’s big long lenses (F2.8 300mm, F2.8 400mm, F4 500mm and F4 600mm and F4 400mm DO), are able to sense you are using a tripod and automatically disable the IS function when required.
3. The IS function actually likes a bit of camera shake in order for it to have an image to make still. If your camera is perfectly still the IS function (via gyros and complex electronics) has nothing to work with/against and gets confused, resulting in a moving image within the lens.
The following links provide further insight:
Link To - Photo Net forum - Part 1
Link To - Photo Net forum - Part 2
Link To - A number of emails, including one very authoritative email from Chuck Westfall from Canon's Technical Department
Canon 500mm F4 IS on Canon 50D body with Battery Grip covered by Wildlife Watching Supplies Lens Cover. Mounted on Wimberley Sidekick, Markins Ballhead and Gitzo Carbon tripod.