Rudolf Kingslake's Lens
in Photography and A History
of the Photographic Lens describe the origins and effects of lens
- 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
- 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
- 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
- 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.
Rudolf Kingslake, Lenses in Photography, 1951;
Rudolf Kingslake, A History of the Photographic Lens, 1989