The Kinesis Foam Doughnut is a padded collar that is designed to stabilize a telephoto lens such as a 300mm f/2.8 or a 600mm f/4 when placed inside a compatible case or bag. The Foam Doughnut is particularly useful for telephoto lens cases that allow a lens to be stored or carried facing downward with or without an attached camera. In such bags or cases, the section of the lens where it narrows to connect to a camera may have room to shift during transport. By wrapping around a lens toward the front of the mount, and locking into place with a touch-tab fastener before the lens is placed inside a bag or case, the Foam Doughnut can prevent such movement.
The diameter the Foam Doughnut will accommodate depends on the bag or case it is used with. If used with a Kinesis L321, L522, or L622 lens case, it provides an opening 2.75" (7.00cm) up to approximately 3.50" (9.00 cm) wide. If used with a Kinesis L311, L511, or L611 lens case, the opening is fixed at 2.75" (7.00cm) wide.