(see also this chapter)
Nippon Kogaku K.K. introduced in 1962 two lenses for its Nikkorex F-mount single lens reflex camera. These two lenses were produced by Mamiya Corp. (founded in May 1940 by Seiichi Mamiya). The production of both lenses stopped in 1966. It is not known (yet) how many were produced.
Nikkorex Sekor 2.8/35 mm.
This wide-angle lens has an optical design of 7 elements in 6 groups (similar to the Nikkor 2.8/35 mm.) and a semi-automatic diaphragm. After any exposure the diaphragm will remain closed. By the sliding lever on the lens mount the diaphragm can be opened again. The lens - weighting in at 305 gram - focuses down to 50 cm./1.65 feet. Standard filters of 52 mm. can be used.
Nikkorex Sekor 2.8/135 mm.
This short tele lens has an optical formula of 4 individual elements. Its filter size is 62 mm. The lens has a semi-automatic diaphragm, too. It can be focused down to 1.5 meter / 5 feet.
The aperture of the two lenses can be set at all full stops and in between 2.8-4 and 4-5.6!
Both lenses are rare and very much collectible. Their optical performance are a bit below Nikon standards, however. Finally: both lenses will fit any Nikon SLR (F-series, Pronea, etc.), even digital SLR cameras. Focusing and metering has to be done manually, however, as the lenses have no aperture prong nor tab.