In many cases, the enhanced transmission of some antireflective
coatings is very necessary. In fact, the advent of antireflective
optics has made new optical instruments containing
many-element apparatuses feasible. For example, a modern
confocal microscope might have 15 or 20 optical elements in
the light path. Borosilicate glass that has not been treated to
eliminate reflections typically has a reflectance of about 4% in
visible wavelengths per surface. A piece of borosilicate glass
with a simple multilayer anti-reflective coating might average
0.7% reflectance per surface. When a single interface is
concerned, the difference between 96% transmission and
99.3% transmission seems miniscule. However, in a
multielement light path, this difference becomes very
significant. If an incident light path crosses 30 air-glass
surfaces, the final transmitted light at the end of the path
would only be approximately 29% for non-anti-reflection
treated optics. An identical path with anti-reflection treated
parts would be 81%.