I can't see any movement of internal parts with my 100-500mm off the camera. It's difficult to see much because the iris stops right down to give a narrow aperture, unlike the 100-400mm II which remains wide open when detrached. Is yours the same?
First to clear up one point: Aperture isn't involved. The IS element that CPS and I see moving around is
the first lens element you can clearly see beneath the front element. If you hold the lens so that the front element is up, and at a bit of an angle so your head isn't blocking light, you can look down and see that element moving around within the inner lens barrel when tilting the lens from side to side or back and forth. Compared to other IS lenses, the gap between the IS element and the collar that restricts its movement is very noticeable. So when I tilt, I can see the element bumping against that collar--and I can feel the vibration with my hands. (In other lenses the movement is slight, more of a very light tapping at the most.)
I thought this was the kind of mild but frequent impact that parking the IS elements on earlier models was supposed to prevent, and according to CPS, this is unexpected to them. But, as I said a few posts up, they would not go so far as to say whether it was a problem or not, just that in their experience, the older IS lens do have a parking mechanism.
So what is the
potential problem, in my opinion? When the lens is attached to a body that has timed out or is powered off, the IS element can bump around freely within the collar while the rig is being carried or transported. The same is true when the lens is not attached to a body. I believe that Canon used to park the IS system for a reason. Maybe they have made changes to construction that make it unnecessary. But unless they can explain what has changed, I foresee the lens developing alignment problems--especially if it is carried a lot while hiking.
I understand usern4cr's plan to carry the rig in such a way as to not jostle the lens while hiking or walking, and that makes sense if one is able to carry the lens by the foot all the time, keeping the lens mostly parallel to the ground with a gentle swaying. This seems fine on a level path. usern4cr also plans to stow the lens in a bag horizontally, from my understanding, which doesn't work well in my Lowepro backpacks--especially if the lens is attached to a body!
Requiring such conscious concern about outdoor/wildlife/sports equipment just seems unfair. I baby my equipment the best I can, but Canon has so spoiled us in the past with rugged gear that, with the L series's reputation and the 100-500mm's MSRP, it's just asking too much.
If I had been past my return window, ok, just pay for the four year CarePak and enjoy the wonderful lens. But since I was able to return, I did so, and I will keep asking Canon for an explanation. Why do they now allow the IS elements to bump around on a 100-500mm super-telephoto, but, according to CPS, kept the IS elements of an inactive 100-400mm II locked down (parked) by default.
Until you can see the actual moving and bumping of the element within that collar, it is very hard to just read about this and believe it's worth returning the lens. Once you do see it, then you can judge for yourself. Like I said, if I were keeping it, I'd get the CarePak, an option I've never paid for in the past.