The WonderPana 66 System from Fotodiox is a kit that combines the Core Unit with the Upgrade Bracket. This allows you to attach different filters to the Sigma 12-24mm f/4.5-5.6 EX DG IF HSM Aspherical lens. The Core Unit accepts all 145mm filters including UV, circular polarizer and neutral density filters. When the Upgrade Brackets are attached, the system holds the 66 filters, which are 6.6 x 8.5" rectangular filters. The core unit also doubles as a metal hood, protecting the front element of your lens. A snap-on lens cap is included and fits onto the metal core unit.