This document describes a "Nun's Knickers" donut adaptor ring that fits into 105mm matte boxes. The elasticated fabric ring stretches over lenses to completely prevent light leaks. It provides a snug fit for donut rings, is made of tough and flexible materials, and is lightweight and easy to install. The "Nun's Knickers" adaptor ring helps photographers using 35mm lenses and adaptors with wide matte boxes to avoid light leaks.