The Takumar 55mm SLR lens is really interesting to me because over 4+ versions of the lens it kept the same optical design but got dramatically improved coating

The Takumar 55mm SLR lens is really interesting to me because over 4+ versions of the lens it kept the same optical design but got dramatically improved coatings every few versions. The single-coated version actually has quite good and natural color rendition in the right light, unfortunately the internal reflections are really noticeable with strong sunlight in the frame. I still consider the version with Zeiss coatings good enough for studio work. Another interesting thing is that the f/1.8 and f/2 versions are both the f/1.8 lens, but the f/2 version has the iris calibrated to be wide open at f/2. Some people prefer the f/2 version because it has less vintage glow wide open while keeping circular bokeh balls.