Nikon Rumors on Twitter: "Collection of selected Nikon patents can be found here (pictured is the lens patent for the Fisheye-Nikkor 6mm f/2.8 lens): https://t.co/ZkMTMfib7B https://t.co/4iQFKXFxSe" / Twitter
Nikkor 6mm f/2.8 Fisheye Nikkor lens
Nikon Fisheye-NIKKOR 6mm f/2.8 (AI and AI-s) – Sample-Image.com
Uber-Rare Nikon 6mm Fisheye Lens on eBay Can See Behind Itself | PetaPixel
Not for the frugal fisheye photographer: Rare Nikon 6mm f/2.8 Ai-S lens available on eBay for around $85k