What not to do with USM (HSM) lenses?

[DocFrankenstein]

I'm just wondering.

Is it ok to turn the ring when the cam is off and the lens is in AF mode?
Is it ok to turn the ring PAST the range scale?
Is it ok to turn the ring while the cam is focusing?

Just making sure. I don't wanna kill my lens.

[timmyquest]

I dont think any of those hurt the lens.

[EoSD30fReAk]

you can do all those things without hurting or killing the lens mechanism

USM ring motors are build to do this.

[Jon]

Not all USM motors are alike. Canon lenses with the ring motor are generally designed to allow you to focus manually even while set to AF. Other USM lenses (such as the 28-90 III) will let you know they don't appreciate such treatment by 1) resisting, 2) grinding and/or 3) refusing to focus when you turn the camera back on - because you've whacked the focus sensor (cure is to set it to MF, rack the lens back and forth, then re-set to AF). Basically - if you do it accidentally, occasionally, it shouldn't cause major problems - but don't make a practice of it, and if it exhibits any of the above symptoms, try VERY hard not to do it again.

[slin100]

Although it might not necessarily cause any damage, turning the focus ring on a FTM focus lens while the camera is focusing creates more work for the focus motor. You especially don't want to do this in AI Servo mode because the camera is constantly focusing and any attempt to manually focus will be countered by the AF system.

[DocFrankenstein]

I have only one lens with the circular ring and it's the 70-200 EX HSM sigma. Cost me a bit, so I don't want to whack it.

Does anybody has a link describing how the motors work? USM/HSM?

[Jon]

Since they're from different manufacturers, it would be hoping for too much that they'd function the same. In your case, I'd search the Sigma site, then try a search for HSM operation. But after looking at their web page on that lens, it sounds like it does support full-time manual focus.