The Tripod Collar A (White) for Canon 400mm & 70-200mm Lenses from Vello is designed for the Canon 400mm f/5.6 L, 70-200mm f/4 L IS, and 70-200mm f/4 L lenses. The ring makes rotating your lens easier and the built-in tripod collar improves lens balance by screwing into the tripod mount. This collar has vertical alignment marks for quickly changing the orientation from horizontal to vertical. Using the included bushing, either a 3/8" or a 1/4" tripod mount can used. Improves Lens Balance The ring secures your lens to the camera"s tripod Gives Your Camera Setup Better Balance The ring adds stability to your camera and lens. Due to its weight, when the lens is mounted with a camera on a tripod, the center of gravity is shifted to the lens. The ring attaches to the tripod and can be shifted to adjust the balance. Rotation Having the camera secured with a ring around the lens makes it possible to rotate the lens between landscape and portrait modes without removing the camera from the tripod. The friction thumbscrews can then be tightened to secure the camera in the desired position. When not needed, the ring can be rotated to an out-of-the-way position Thumbscrews Tighten And Loosen Ring Having thumbscrews control the ring makes it easy to adjust the tripod ring on the go Lens Compatibility: Canon 400mm f/5.6 L, 70-200mm f/4 L IS, and 70-200mm f/4 L lenses Tripod Mount Thread Size: 3/8" & 1/4"