The Nikon Nikkor-O 21 mm f/ 4 is an ultra wide-angle prime lens for Nikon F cameras.
This is the first Nikon F wide-angle lens. It originated in the epoch of Nikon rangefinder cameras. It is very compact ("pancake" lens). Besides, its rear elements protrude deeply into the body. It requires the use of a mirror lockup and a separate optical viewfinder. The Nikon Nikkor-O 21mm f/4 can be used on Nikon F, Nikon F2 cameras only, because besides a mirror lockup it requires a special latch on a camera bayonet to secure correct positioning.
At the moment of release the Nikon Nikkor-O 21 mm f/ 4 was the most extreme wide-angle lens, produced in Japan. There existed a bit less fast Biogon 21 mm f/ 4.5 lens for Contarex cameras.
Links to online resources:
Posted by: Nik_SSG Date of publication: 23.07.2011