A close-up filter is a converging glass used for close-up and macro photography, and works in the same way as spectacles used for reading. The insertion of a converging glass in front of the taking lens reduces the focal length of the combination.

Close-up lenses are usually specified by their optical power, the reciprocal of the focal length in meters.

Original Nikon Made in Japan filters, much higher quality than hoya, tokina etc..

52mm is good for nikon 50mm AF lenses or any of those nikon old AI/AIS lenses..