The Genus GARD-NK Nun's Knickers Do-nut Adaptor Ring (so called as an industry tongue-in-cheek nick-name) is a do-nut ring fitted with a black-out fabric cover that wraps around the barrel of your lens to block out any light completely. The 105mm plastic ring fits snugly into your matte box and the elasticated fabric cover wraps around the barrel of your lens. The flexibility of the fabric ensures that it can be used with lens diameters 72mm upwards.