The 100-400 I dropped at the airshow came back from Canon. One thing I noticed is that while carrying the lens in my hand, I can feel something clanking around in it. When I engage the AF, this same thing goes clunk at first. Is this from the IS system's floating elements? I can't say it appears to have affected picture quality, which is once again damn good. (I even put a Kenko macro extender on it, and can't believe what I'm shooting.) Nevertheless, I'm concerned about the clink/clank inside; 'didn't notice this before at all.
Second, I found that on a monopod, this lens balances very poorly once you've stretched it out to 400. Simple physics there. So I tried taking the lens collar off and actually putting it around the barrel; the collar was a b---- to get off, and now something inside the collar that the screw fit into is rattling around, and I can't tighten the screw to get the collar back on!
If you don't want to rely on the IS always, does another manufacturer make a better-balancing collar guismo for this lens?
Mine doesn't seem to rattle. If the locking ring is set to the smoothest position then a faint noise can be heard. But it's not very audible and would go unnoticed except in a very very quiet room. With an extender, there's more mecanical play between the lens/extender/body and some clunking.
I can't say anything about your lens collar. Did you tighten it too much and stripped the threads? See below for a technical description (with parts) of that lens collar.
The operating mode of the 100-400 (pump) is somewhat difficult to balance but you may want to read this [a href=\"http://www.reallyrightstuff.com/tutorials/monopods/index.html]RRS article[/url] on monopods. If you have a long lens plate (not a short one made for the 100-400) attached to your lens collar, you could slide it forward or backward in the clamp to find the best balance. Check out Wimberley website
. The plates feature dual safety stops and are compatible with RSS lever clamps.