Lens pr0n: The Nikkor 6mm f/2.8 fisheye monster | TechCrunch
This Uber-Rare Nikon 6mm f2.8 Fisheye Lens Can See Behind Itself - The Phoblographer
Extremely Rare Nikon 6mm f/2.8 Fisheye Appears on eBay for $146,000 | PetaPixel
Deal of the day: Nikon Fisheye-Nikkor 6mm f/5.6 circular fisheye lens for $5,999 - Nikon Rumors
This Uber-Rare Nikon 6mm f2.8 Fisheye Lens Can See Behind Itself - The Phoblographer
File:Fisheye-Nikkor Auto 6mm f2.8 lens 2015 Nikon Museum.jpg - Wikipedia
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