This is rare lens, about 300 made in Leica mount and maybe 500 made in Nikon S-Mount. This lens was replaced within a year by the Nikkor-SC 5cm F1.4. As per Pete Dechert's "Canon Rangefinder Camera"- the 5cm F1.5 was designed in 1937 for the Hansa Canon. It never made it into production before the war. I am guessing that Nikon needed a Super-Speed lens on the market while the F1.4 was being designed. It also may be possible that Nikon had a small supply of the glass used in the design, enough to do the small run. David Duncan Douglas used a Nikkor-SC 5cm F1.5 for most of the pictures in his book "This is War".