Rudolf Kingslake's Lens in Photography and A History of the Photographic Lens describe the origins and effects of lens coatings:

  • H. Dennis Taylor, in 1896, was the first to observe the effect of coatings "when he noticed that some old lenses having dark tarnished surfaces transmitted more light than a new lens of the same kind."
  • In 1936, Professor John Strong suggested that depositing a thin layer of a low index material on lens surfaces could reduce surface reflections.
  • Also in 1936, A. Smakula of Zeiss invented the process of vacuum deposition on glass elements.
  • Calcium fluoride was first tried, but was soft and could only be used on inner surfaces. It was heated to varying temperatures, each forming a different tint; brown was the most effective.
  • Commercial calcium fluoride coatings were first available to manufacturers in 1938.
  • Harder fluorides coatings and improved vacuum deposition techniques were developed in the 1940s.
  • Later research produced multicoating where several layers of differing materials are deposited, each of which has a slightly different sensitivity, so that reflections across the entire visible spectrum are reduced.
  • Coatings "(a) ...reduce ghosts and flare spots, and (b) increases the light transmitted by the lens in the highlight region (of the image) and reduces it in the shadow region."
  • Lens/film speed indices vary depending on whether these are measured by the density of the highlights or the density of the shadows.
  • Coatings have the most profound effect when a low contrast subject is photographed against a strong backlight.
  • Barrel reflections are the next most important source of stray light. These are most effectively prevented by knife-edged, strategically-placed baffles.
  • Dirt and smudges on lens surfaces can have a profound effect on contrast.

Source: Rudolf Kingslake, Lenses in Photography, 1951;
Rudolf Kingslake, A History of the Photographic Lens, 1989