Why are lenses often coated with thin films of transparent material ?

What is a transparent material ?

Name four transparent materials.

To ensure almost 100% transmittivity, photographic lenses are often coated with a thin layer of dielectric maerial, like MgF_(2)(mu=1.38) . The minimum thickness of the film to be used so that at the centre of visible spectrum (lambda = 5500 Å) there is maximum transmission.

Determine what happens to the double slits interference pattern if one of the slits is covered with a thin, transparent film whose thickness is lambda/(2(mu-1)) , where lambda is the wavelength of the incident light and mu is the index of refraction of the film.

Thin Film Interferance

Thin film interference

Interference By a thin film

On face of a glass (mu = 1.50) lens is coated with a thin film of magnesium fluoride MgF_(2)(mu = 1.38) to reduce reflection from the lens surface. Assuming the incident light to be perpendicular to the lens surface. The least coating thickness that eliminates the reflection at the centre of the visible spectrum (lamda = 550 nm) is about