Aurora Aperture unveils new rear mount filter system for Canon, Nikon, Sigma & Sony ultra wide-angle lenses: Digital Photography Review
Amazon.com : NEEWER 58mm Lens and Filter Set: Wide Angle/2.2X Telephoto Additional Lens for 18mm-85mm APS-C Lens, (+1+2+4+10) Close Up Macro/ND/UV/CPL/FLD Filters for Camera Lens with ⌀58mm Thread : Electronics
Canon EF-M 15-45mm f/3.5-6.3 IS STM 0.44X High Definition Super Wide Angle Lens w/ Macro + 3 Piece Lens Filter Set - Walmart.com