The WonderPana Free Arc XL provides the freedom to use round 186mm filters on your Wide and Ultra-Wide Angle Lenses. Because of the construction of these lenses, it's normally impossible to install filters as there are no filter threads. Additionally, standard filter sizes are not large enough to adequately cover the lens's wide angle view. The WonderPana Free Arc XL changes all that by providing a complete kit for mounting our collection of both round and square filters (with optional upgrade brackets). The all-metal Core attaches directly onto the lens with a secure mounting system. With The Core in place, you can now mount any of Fotodiox's 186mm round filters. PLEASE NOTE: The WonderPana Free arc XL you see on this page is custom engineered to fit the Canon EF 11-24mm f/4L USM Lens. It will not fit other lenses, so it's important that you chose the correct Wonderpana Core system for your particular lens model. You will have to remove your lens from the camera in order to mount the filter holder.