I know it sounds obvious but I don't know much about big lenses on cameras and tripods. I've never owned anything like that. I read about a tripod collar but thought it was for keeping a zoom (push pull) from sliding around. Then I read someone talking about a tripod mount for their 500mm lens. Further, I've seen the small "piece" on the bottom of some lenses where it meets the body but have no idea what it is. Thanks. I think there's a question in there somewhere.