The f:32 minimum aperture denotes a Gauss type version. The earlier versions were a Sonnar derivative and had f:22 as a minimum. Factory Ai lenses had a step in the rear of the aperture ring as well as an extra scale of (smaller) aperture numbers to be show the aperture in use in the viewfinder, non-Ai lenses that were modified do not have the second scale. Sonnar or Gauss, Ai or pre-Ai, it's a superb lens.
Originally Posted by Soeren