This is a meniscus convex lens from about 50 years ago. When the camera lens is set to infinity, it focuses at a distance of 33 cm from the lens tip. Extending the helicoid allows focusing at distances closer than that. It cannot focus on subjects further than 33 cm. This is equivalent to Kenko's No. 3. Incidentally, Asahi Optical did not develop No. 2 or later, although they did manufacture No. 1 at the time. As it is an old item, there are scratches, dirt, and coating burns.