Tamron uses advanced multi-coating techniques to suppress internal reflections that cause 'ghosting' (secondary images) and 'flare' (low contrast, washed out images). As soon as light hits an untreated glass surface, a part of it is reflected. The average reflecting degree on untreated glass surfaces amounts to 5 %-6 %. This leads "to ghost images" and to loss of luminosity and contrast.
Tamron developed this coating technology to suppress these reflections, and to achieve the best possible color balance. The coating is applied to all Tamron lenses. An improved BBAR coating allows for even better light transmission with long, as well as with short wavelengths.
The decrease in reflection is reached via interference. The technology used here, is based on the fact that reflected light waves with the same amplitude extinguish themselves with an optical path difference of λ/2.
Consequently, nanometer layers of magnesium fluoride are applied on the glass surface from whose interfaces the light waves are reflected.
If a suitable layer thickness is chosen, the reflected waves will extinguish themselves the reflecting energy it is converted into transmission energy, so that the reflected light wave is transmitted instead of being reflected.
The following diagram clearly shows this correlation for a certain glass. On the left the reflecting degree is applied in % and below the wavelength of the light. The reflections clearly decrease with several coating layers throughout the entire wavelength area.