The EF70-200mm f/4L IS USM has the ability to detect when it is mounted on a tripod. If you keep the shutter button half-pressed, or better yet, use a remote switch to simulate a half-press, the stabilizer mechanism will drift the image downwards for the first second or so, then the mechanism will stop moving. (It's for this reason as well as battery power conservation issues that the instruction booklet recommends shutting off the IS system while the lens is mounted on a tripod.) You can see the effect if you look through the viewfinder while half-pressing the shutter button. However, it is important to understand that this form of disabling is different than shutting off the IS function with the mode switch on the lens. In the latter case, the IS mechanism is centered and locked into place, whereas in the former case, the IS mechanism shifts the image downward slightly for a second or so, then stops moving. It's not moving, but it's not centered or locked, either. It's effectively on standby, so that it can resume its corrective capabilities instantly if movement is detected. Again, you can see this for yourself by looking through the viewfinder while pressing the shutter button halfway for at least several seconds, assuming the lens is mounted on a tripod and the IS switch is on. To my way of thinking, this is not the optimum way to use the equipment. In my opinion, if you use the EF70-200mm f/4L IS USM on a tripod, it would be best to turn off the IS mechanism via the switch on the lens, rather than depending on the tripod detection capabilities of the IS mechanism. (źródło:
http://www.digitaljournalist.org/iss...tech-tips.html)
