Umbra is a high quality absorption coating with light reduction levels of 25, 75 or 85%, applied to one side of glass lenses in a vacuum deposition process.
The attractive brown tint guarantees the natural rendition of all colours. The vacuum deposition process results in a uniform tint over the entire lens surface, regardless of the dioptric power. The lenses with light reduction levels of 75% and 85% shield the eyes against strong glare and provide reliable protection against solar UV radiation.
Light reduction of up to 97.5% is possible if an Umbra coating is applied to both the front and back surfaces. With a light reduction of >92%, the lenses are no longer suitable for use in traffic!
With three different light reduction levels, Umbra-coated lenses cover an extremely wide range of applications:
The vacuum deposition of a thin absorptive coating on glass lenses was one of the first coating techniques to be implemented on a large scale in the ophthalmic field. Carl Zeiss introduced the Umbra coating on Punktal lenses as long ago as 1964. In 1992 a successful attempt was made to enhance this method with the aid of new technologies and to improve the quality of the coating even further. For the first time, it was possible to match the composition of the coating material optimally to the lens material. The residual reflection of Gold ET and Super ET, for example, has the same colour and the same intensity for all refractive indices and all Umbra tints (25, 75 and 85%). The new technology permits extremely high reproducibility of the coating properties.
The Umbra coating is deposited in vacuum installations in much the same way as an AR coating. In the development of the new Umbra coating, Carl Zeiss has succeeded in depositing material mixtures with different deposition properties in a conventional way. The material mixture consisting of various metal oxides is pressed into cooled metal crucibles by the application of high pressure and evaporated with the aid of an electron beam vaporiser. This makes it possible to deposit the components of the material mixture simultaneously, resulting in a homogeneous layer.
Substrate temperatures of 250 to 300 °C must be reached to obtain the required coating hardness. The thickness of the absorptive coating is checked constantly with the aid of sophisticated measuring techniques during the deposition process.