This lens is "uncommon", probably under 3500 made. This lens is a Planar formula design, 7 elements in 4 groups, a 1-3-2-1 configuration. The front doublet of a traditional Planar is replaced with a triplet, each element of lesser power than what would have been required to get the F1.5 speed from the traditional design. Using the triplet eliminates two air/glass surfaces that would be required in a 7 element/ 5 group design used in the Leica Summarit. I believe the Simlar is the first original post-war Japanese design. The Canon and Nikkor lenses were based on existing Sonnar and Planar designs. This is the first 1-3-2-1 Planar that I've seen, the Canon 85/1.5 also used this basic block diagram. This lens was bought on a 4-digit Leotax D-IV, made in 1950. I have seen it described as "half a Sonnar"- because it used a triplet as the second group. This is not correct, it is a Planar. The focal length of the front section and rear section are "roughlt" the same. A Sonnar formula lens, the front section is a telephoto with focal length "about 2x to 3x that of the rear section.