Nikon 6T Close-Up Lens
The linked website puts the Nikon single-element 0,1 and 2 close-up lenses in the not-so-good category. In about 1976 Modern photography tested a number of macro lenses. The 50/2 Nikkor with one of the single element Nikon close-up lenses was sharper when closed down a little than some of the purpose-built macro lenses. I just bought a set of three 49mm 2-element Minolta close-up lenses for a very modest price. They are apparently NOS. I already had a set of the Minolta close-up lenses in 55mm. Konica made a two piece set of 2-element close-up lenses. Other interesting close-up lenses were made by Topcon and Olympus. Minolta made a close-up lens which was sold with its old 80-160 zoom. I use it with a 400/5.6 Konica UC Hexanon. The combination gets me close enough for a tightly cropped portrait.