Haida Rear ND Filter Kit for Sigma 14-24mm F2.8 Lens E mount & L mount 14mm F1.4 | eBay
Using Neutral Density Filters with the SIGMA 14-24mm F2.8 DG DN Art Lens | SIGMA Blog
NiSi 150mm Q Filter Holder For Sigma 14mm f/1.8 DG HSM Art Lens (Discontinued) | NiSi Optics USA
Rear Lens Nd Filter Kit For Sigma 12-24mm F/4 Dg Hsm Art Lens Canon Ef Mount & Sigma 14-24mm F/2.8 Dg Hsm Art Canon Ef Mount - Camera Filters - AliExpress
Amazon.com : JJC 55mm Variable Neutral Density Filter ND2 to ND400, Slim Fader ND Filter for Sony A6600 A6500 A6400 A6000 with E 18-135mm f/3.5-5.6, Sigma 56mm f/1.4 DC DN Lens& More