The MK1 Fisheye Protector helps protect the surface of The MK1 Lens (A.K.A. The Death Lens / The Mark 1 Lens / Century Precision Optics DS-FEWA-00 0.3x Ultra Fisheye Adapter Lens).

100% unobstructed field of view (No vignetting)
Straightforward design and easy to attach
Outside (convex side) coated with scratch resistant military grade hard coating – tadashifilters.com