Many camera companies evolved from optical houses and made products like microscopes. Nikon is no exception. Nippon Kogaku made many optical products before its famous F SLR was used in the Vietnam war and later introduced to the USA.
Once Leitz developed a device to connect a 35mm camera to a microscope, others jumped on the band wagon. This included Japanese optical houses. Nikon’s FX-35DX camera shown here was specifically made for scientific use such as on microscopes. No rangefinder. No viewfinder.
This version has a Nikon mount but can also come with a Leica bayonet-mount to fit the Leitz MIKAS. Many microscope makers moved from glass plates to 35mm cameras using special devices like the MIKAS to accurately focus and frame microscope images on the film.