Why is there IS on the super tele photo primes?

I thought IS is supposed to be turned off when using a tripod. Is it really practical to handhold a 12lb lens?

My best guess would be monopod usage. I see this alot.

Monopod for sure.

I don't see too many tripods being packed around an F1 paddock these days...

actually, the new version(s) of IS can be used on tripods, it's just the older IS, like that found on the 28-135mm that you have to turn IS off when using a tripod.

MOnopods, though the 300/2.8 and to a lessor extent, the 500/4 can be handheld.

deadpass wrote in post #2151541
actually, the new version(s) of IS can be used on tripods, it's just the older IS, like that found on the 28-135mm that you have to turn IS off when using a tripod.

i thought the newer IS will automatically shut off when on tripods.

Tom W wrote in post #2152527
MOnopods, though the 300/2.8 and to a lessor extent, the 500/4 can be handheld.

And thats a factI hand hold my 300f2.8Lis all day with no problems at all yet people say that the 70-200f2.8Lis it to heavey lol.

From the Canon CPS Knowledge Bank...

But these recommendations above (the previous paragraph was talking about switching IS off on a tripod) do not apply to the 28-300/3.5-5.6L IS, 70-200/2.8L IS, 70-300/4.5-5.6 DO IS, 300/2.8L IS, 400/2.8L IS, 400/4 DO IS, 500/4L IS, and 600/4L IS. With previous IS lenses, it was necessary to turn off the Image Stabilizer when using a tripod because it might operate incorrectly. But the Image Stabilizer installed on these IS lenses has an additional function that prevents improper operation when using a tripod. It also corrects camera vibration caused by slow shutter photography when using a tripod: a common problem with super-telephoto lenses. About one second after the shutter is pressed halfway, the unit automatically determines that a tripod is being used from the output of a vibration gyro.

These lenses effectively have two IS modes within Mode 1. The decision about which mode will be used is made by the equipment, not the photographer, based on an evaluation of the degree of detected movement, as follows:

- When the lens is mounted on a steady tripod and the shutter button is pressed halfway, the IS begins to operate immediately and the image in the viewfinder goes through a very slow vertical shift for about 1 second. After that, if the shutter button continues to be pressed halfway, the IS mechanism automatically goes into a special mode which is designed to detect and correct for mirror slap and shutter movement at slow shutter speeds. Based on tests, it does this job spectacularly well. Close examination of results from shooting tests definitively proves that there is no advantage to be gained by shutting off IS, or even by locking the mirror prior to exposure.

- When the lens is mounted on a monopod or hand-held and the gyro sensors detect movement exceeding a certain rate, the IS mechanism switches into its conventional correction mode which is designed to compensate for relatively gross and/or erratic lens movement.

If you want the best possible results when working from a tripod with an IS lens that supports 'tripod IS', you have to let the mechanism operate for at least 1 second before shutter release. If you're really serious about it, use an eyepiece magnifier to confirm that the IS mechanism has settled down, and also use a remote switch so you don't have to touch the camera body when releasing the shutter.