|With accessory frame viewfinder|
image by Rick Soloway (Image rights)
The 1961 Calypso underwater camera was created and manufactured in France, inspired by diving pioneer Jacques-Yves Cousteau, and named for his research ship.
Soon its design was licensed to Nikon who re-introduced the camera in 1963 as the Calypso/Nikkor in Europe and Nikonos elsewhere. The Nikon version slightly altered the exterior appearance, with smooth black rather than "crinkle" finish, and with black diamond-pattern surfaces for gripping. The standard lens was now a 35mm f/2.5 Nikkor, adapted to use the distinctive side control knobs of the original Calypso. This first Nikkor version has a single distance scale (meters or feet, not both); and lacks any white lines to indicate which knob controls focus vs. aperture.
With the introduction of the Nikonos II in 1968, the original Japanese model became known as the Nikonos I but is not marked as such.