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Lensfinder.com - Ultra Rare Nikkor 6mm f/5.6. Only a few hundred of these lenses exist. This lens has a 220 degree field of view for Full Frame 24x36mm sensors. Made in Japan
Nikon Fisheye Nikkor 6mm f/2.8 Lens
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Rare Lens] $160,000 Nikkor 6mm 2.8 Fisheye Can See Behind You | Fstoppers