This high-quality optical glass dome port, which has a N120 mount, is recommended for the best possible results with fisheye lenses. This dome port is much smaller than the glass or acrylic 8-inch ports. It gives excellent results with fisheye lenses on full-frame cameras, especially with the Sigma 15mm fisheye lens. *Keep in mind, full frame wide angle lenses still need their apertures to be stopped down to avoid mushy/smeared corners.* f10-f22 is the gerneral range to keep full frame fisheye lenses in with this dome. Exceptions are with big animals or divers in the blue where nothing important falls in the corners.