What is the T* XP ?

Anti-refection coatings have proven to be one of the most important inventions in modern optics. By reducing the natural tendency of glass-to-air surfaces to reflect a portion of the incoming light, they ensure that the maximum amount of light reaches the film instead of being reflected away from the lens surfaces or, worse, bouncing around inside the lens. Thanks to modern anti-refection coatings we are used to brilliant images in almost all lighting situations on the film set.


History

First developed in the Carl Zeiss laboratories in 1935, anti-refection coatings found widespread adoption after 1945. These first coatings were single layer coatings which optimized transmission for one color only, leading to an uneven transmission behavior across the color spectrum. A significant improvement was introduced in the 70s when multilayer coatings were introduced, offering a further reduction in reflectance from glass-to-air surfaces in a broader spectral range. A highly sophisticated version of this technology is the Zeiss T* coating used in the ARRI/Zeiss Ultra Primes and Variable Primes.

T* XP

Originally developed for the ARRI/Zeiss Master Prime lenses, the multi layer T* XP (Extended Performance) anti-reflection coating ensures maximum transmission in a wide spectrum of wavelengths. The T* XP coating has been optimized with respect to the spectral sensitivity of motion picture film and the sensitivity of the human eye.

 

Designing the proper coating formula is one part of the high art of anti-refection coatings. The second part is the equally tricky art of applying the coating in the proper and even thickness to the lens elements. Zeiss uses a carefully monitored, elaborate process in high vacuum where special optical substances are evaporated one after the other and deposited on the lens surface with precisely controlled thickness. For the T* XP coating this process was further refined to assure a perfectly even and symmetrical application. It assures uniform performance across the whole lens surface from the center all the way to the edges. This is especially important on lenses with large, strongly curved surfaces. When compared to conventional multilayer coatings, the T* XP coating has up to five times better transmission at the edges.

 

The result is higher contrast, deeper blacks and a great reduction of false light effects such as internal reflections, veiling glare, flare and narcissism. In combination with proper internal lens construction, the T* XP coating ensures that the lens can easily handle tricky lighting situations like strong backlight, sunsets or car headlamps. Lenses using the T* XP coating can catch subtle tones in the deepest shadows and fully utilize the high dynamic range of modern film stocks.