The Cavision Matte Box Donut Adapter Ring has on outer diameter of 85 mm and is designed to work with select Cavision matte boxes. The donut adapter prevents light from leaking around the lens and reflecting off filters in the matte box. The cloth features an adjustable sizing cord that allows you to fit lenses with an outer diameter of approximately 50 to 85 mm without having to swap out donuts.
The aluminum ring of the donut adapter fits into the back of the matte box, and the cloth fits around the lens. The adjustable sizing cord allows you to snug the cloth around the lens. The cloth also extends up to 45 mm away from the matte box, which makes this donut usable with lenses that have a front that moves forward and back.