DIY ND Filter Holder for Wide Angle Lenses Demo with Panasonic 7-14mm - YouTube
FilterDude 62mm LEE Compatible Wide Angle Adapter Ring for Filter Holder | eBay
Lens filters for special wide-angle and ultra wide-angle lenses
49mm 0.45x Super Wide Angle Lens W/ Macro & Filter Lens Adapter Ring Tube For Ricoh Gr Iii Iiix Griii Gr3 Griiix Gr3x Camera - Lens Adapter - AliExpress
Lee Filters 82mm Wide Angle Adapter Ring
Fotodiox Fotodiox WP145-Core-TMR1530-Cap WonderPana Filter Holder for Tamron 15-30 mm SP F-2.8 Di VC USD Wide-Angle Zoom Lens and Ultra Wide Angle Lens Filter Adapter at Lowes.com
Amazon.com : Lee Filters 72mm wide angle adapter ring : Electronics