The Cavision 85mm to 77mm Threaded Metal Deep Offset Step-up Adapter Ring is useful for clamping on a matte box when the matte box needs to be pushed back quite a bit further on the lens, to avoid vignetting. It is recommended for clamp-on use when using wider angle DSLR lenses, as it will allow the matte box to sit further back in relation to the lens front; it is especially useful for this purpose. This adapter ring screws onto the lens front filter thread.