I don't mean to be a thread hijacker, but I think this might correlate to the initial question.
I'm a little confused with regards to the Wimberly sidekick. I'm thinking about getting the Canon 500mm f/4L IS lens and a Wimberly head to go with it. But according to Wimberly's website, one of the prerequisites for the Wimberly Sidekick is, "Your lens must have a rotation collar and an Arca-Swiss style quick-release plate." Yet on B&H's website it states for the Canon 500mm f/4L IS lens, " Tripod Collar: Yes (Fixed)". Well, I'm confused. I've read that others, and specifically Michael Reichman, have used the Sidekick along with the 500mm lens, but isn't there a contradiction here? Can someone confirm that they work together and that you'll be able to rotate the camera/lens to either horizontal or vertical while using this equipment combination?