Canon's 800mm IS on a tripod - IS moves a lot!

Greetings All,
I just posted this same question on the Canon Digital Photography forum and most of the responses related to general IS and switching it off while lenses were on a tripod (not applicable to the newer IS generations, correct?). I figured some birders here might own an 800mm...

I gather the IS on the 800mm states - "IS system is tripod-sensing - it shifts into a secondary stabilization mode when mounted on a tripod - it specifically helps correct mirror slap"

I just had my Canon 800mm (purchased in 2010) serviced by Canon and I was double checking the autofocus with the LensAlign MrkII. I noticed while in live view at 10x magnification just how much movement was happening with the IS on - please see this video - http://youtu.be/_T8REC007iE - the video starts with IS off and then on and off a few times.
For the video - 800mm was on a gitzo carbon fiber tripod with a Mongoose 3.6 gimbal tripod head and inside the house, so no wind (and I wasn't dancing...)
I then did a few comparisons of images at low shutter speeds (1/30) and found the images with IS on were fuzzier than those with IS off. I had the lens sitting on the floor with two solid contact points touching the floor - tripod plate and camera battery-grip. Also, I used a remote shutter release.

I guess my real question is for those of you with experience with the 800mm - is this much movement normal? and should there be a loss of sharpness with IS on at shutter speeds of 1/30? I recall reading in A. Morris's Bulletins about using his 800mm at 1/30 and how pleased he was with the results (I assumed the IS was on?). I'd say it was my poor technique that produced the lower quality images with IS on, but I took 5 comparisons and all yielded the images with IS off images to be the sharpest.

Thanks all for your time and in advance for any feedback.

-Ronan

When shooting my 500mm super-tele on a tripod I find that performance is better with IS on. However, you must be careful that the IS has had a moment to "spool up" and stabilize. Try this. Focus and lock the lens down, then go to live view and 10x. With IS off, touch the lens and see if you can see motion (you can). Next, using the remote release, start the IS and see if there's some initial "jiggling". With my rig there is much jiggling when the IS initially comes on. Now, keep the IS for a second so that the view stabilizes and then release the shutter. With my 7D and 5D MkII, the 500mm is more stable with IS on, but only if I make sure that the IS is up to speed.

The way to get sharp images with IS on is to use the normal "bend the lens" technique then IS works well down to 1/30. However at slower speeds and if you are not touching the lens then you can turn IS off.

Hi Ronan,

Yes, the IS system normally drifts when first engaged. It takes a couple of seconds for the drift to settle down. A 1/30 second and slower exposures will have degraded image quality if made while the image is drifting.

Roger

Hi Ronan- It is normal behaviour. My 500mm f4 lens did exactly the same thing.

It looks normal to me. I don't find the "tripod detect mode" effective despite Canon claims, even on much shorter lenses such as 70-200. image will drift and cause blur at slower SS. 1/30sec is a bit tricky, it depends on your technique and tripod/head, but your lens is OK.

I use mine with IS engaged all the time. I have tested both ways on a sturdy tripod and see no difference at proper shutter speeds for focal length. For moon shots with live view I get better results with it off at slower shutter speeds though.

And yes it does move around a lots at first engagement but not nearly as much as my 500mm drift.