We generally attach our camera to a tripod by using the tripod mount at the base of the camera. While this does not pose any problem with lightweight lenses, its a different matter when using heavy lenses; a heavy lens attached to a camera body can cause the lens/body mount to flex and if the lens mount is not strong enough, the weaker section could break, resulting in permanent damage to the lens and/or camera.
With this in mind, some heavy lenses are provided with lens collars. The collar’s foot has a thread for attaching the lens to a tripod. This arrangement not only prevents a potential disaster, but also allows for easy vertical composition by merely rotating the lens within the collar. Unfortunately, the original lens collars are often poorly designed, with a result that the lens wobbles during exposure, robbing us of critical sharpness that the lens could otherwise offer. This has prompted some independent manufacturers to provide special, better designed collars. Two such manufacturers that come to mind are USA based Kirk Enterprises (www.kirkphoto.com) and Really Right Stuff (www.reallyrightstuff.com). They make various useful accessories based upon customer feedback.
Shown here is a Kirk lens collar for the recently introduced AF-S Nikkor 80- 400 f/4.5-5.6G ED VR. Compare it with the original Nikon collar. The accessory collar is a definite improvement. Expensive? Yes, but it sure helps you to achieve the maximum sharpness out of your expensive lens!