Not for the frugal fisheye photographer: Rare Nikon 6mm f/2.8 Ai-S lens available on eBay for around $85k
Nikon 6mm f/2.8 Nikkor Fisheye Overview - YouTube
The remarkable Nikkor 6mm f/2.8 Fisheye - Japan Camera Hunter
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Massive Nikon 6mm F2.8 Fisheye Lens, Yours For $160,000
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
Uber-Rare Nikon 6mm Fisheye Lens on eBay Can See Behind Itself | PetaPixel
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Rare Nikon 6mm f/2.8 Lens Listed on Yahoo Auctions for 13 Million Yen - Resource
Nikkor 6mm f/2.8 Fisheye Nikkor lens
Nikon's 6mm f/2.8 Fisheye on a Z 9 - first time ever? - YouTube
Sample Footage Shot with the Ultra Rare Nikkor 6mm f/2.8 that Can See Behind Itself | PetaPixel