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 & 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.