The D/Focus Systems D/Matte Matte Box is a clip-on matte box featuring an 86mm lens opening, and includes an adjustable French flag, two 4 x 4 filter slots (one of which is rotating), and an 86 to 82mm step down ring. The 86 to 82mm ring will let you mount any lens with an 82mm filter diameter. For lenses smaller than 82mm, D/Focus Systems sells separately 82mm-to-below step down rings that can be attached to the 86 to 82mm ring, thus creating a step down beyond 82mm.
D/Matte is designed at an affordable price-point with the DSLR hobbyist in mind, but is compatible with all lenses that are 86mm and below in diameter.