Milestones in lens designs, in my view, in chronological order:
- Lens coatings (single coating), circa 1920s or 1930s; universally applied from the early 1950s onwards.
- High refraction index glasses (i.e. Thorium glasses), circa 1930-40s but kept secret by Kodak, starting to be used more from the early 1950s.
- Use of electronic calculators for ray tracing, circa 1950s in Germany (Zuse computers)
- Retrofocus lens applied to 35mm cameras (Angenieux, early 1950s)
- First japanese electronic computer, the FUJIC (Fuji Photo Optical, 1956)
- More ubiquitous use of computers for lens design and optimization (circa 1968 and later)
- Artificial fluorite lenses: Canon 1969
- Aspheric glasses used on production normal lenses: Canon 1971
- Multi coating applied ubiquitously: Zeiss and Pentax, 1970 or 71.
later than that:
- Glass molded and "resin"-molded "hybrid" aspheric glasses: early 80s, many manufacturers (i think Canon was the first)