Every AR coating exhibits some residual color seen in the reflections of even a multi-layer coating. The color is significantly less in a multi-layer coating as compared to a bi-layer coating, however. The variations in color and intensity sometimes helps to identify the manufacturer of the coated product.

If a five layer coating is better than a two layer coating, does that mean that a 20 layer coating would be better still? AR coating efficiently is not directly improved by the number of layers, so much as by what each layer contributes to the reduction in reflection. Once again, the formulation of types and thickness of each material to be used in the five layer matrix becomes the priority in this very highly technical area of optics.

In fact, it is only due to refinements in both coating equipment and computers used to run them that these multi-layer coatings can be enjoyed by the patients. The actual process of AR coating has evolved significantly over the last 50 years and is truly a state-of-the-art �high tech� process which utilizes a vacuum deposition technology. Modern AR coating equipment has been known to cost between $500,000.00 and $1,000,000.00.

To begin the process, lenses must be carefully inspected for scratches or surfacing imperfections. Lenses are thoroughly cleaned to ensure good adhesion of the coating to the surface of the lens. Sophisticated ultrasonic cleaning processes are used by most coating companies, which utilize many cleaning and rinse cycles.

Once thoroughly cleaned, the lens is inspected once again to make sure that it has been properly cleaned (if a wax has been applied to hide lens imperfections this cleaning will remove the wax, highlight the scratches and make them more visible after coating). Rejected lenses will be returned to the lab to be remade.

The lens is placed in a degassing oven to assure that all moisture has been removed. This is an important step to make the coating process faster and efficient.

A typical vacuum coating machine has a rotating lens rack at the top of the unit. A monitoring device measures coating thickness. The machine actually measures the change in the frequency of an oscillating quartz crystal. The frequency of the crystal changes as the coating builds on its surface. Optical monitors can also be used in some cases. As the coating builds with the oscillating quartz crystal, the mechanical energy is changed to electrical energy and is fed into a computer for precise layer thickness. The composition and formulation of the materials evaporated onto the lens are proprietary. An electron beam gun evaporates the material to be used in the coating application. Vaporized molecules travel through the chamber to adhere to the lens surface. In a multiple layer coating system the computer controls the time and sequence of the deposition of coatings per side during operation.

AR coating equipment

High Tech process utilizes a vacuum despotion technology

Ultrasonic Cleaning Process

Degassing oven removes moisture from lenses

Rotating lens rack helps monitor coating thinkness