Revar Cine Wormhole 30mm is a large diopter apporoximately the size of a +3 diopter with circular etching to create a unique effect. There is a center flat polished window to allow selective focus in the center of frame. The center flat window in this model is 30mm, perfect for long focal lengths or a small clear area on wider lenses. Made from Schott B270 glass to the highest tolerances.