This is a meniscus-type convex lens from approximately 50 years ago. When the camera lens's distance scale is set to infinity (∞), the focus is at a distance of 33 cm from the tip of the lens. When the helicoid is extended, the focus shifts to closer distances. It cannot be used to photograph objects further than 33 cm away. It is equivalent to a Kenko No. 3 lens. Incidentally, Asahi Optical (Pentax) manufactured No. 1 at the time, but did not develop any lenses numbered No. 2 or higher. Being an old item, it has scratches, dirt, and coating degradation.