The Science of Sight: Why Eleven Spectacles Chooses ZEISS Optics

A legacy written in light: 180 years of ZEISS

Every Archē frame is fitted with lenses from ZEISS. Carl Zeiss opened a workshop for precision mechanics and optical instruments in Jena, Germany, in 1846, and soon concentrated on microscopes. In 1866 he brought in the physicist Ernst Abbe to help improve them, and Abbe's methods later spread to other fields of optics.

Two milestones matter for the lenses in our frames. In 1912, ZEISS launched the PUNKTAL spectacle lens. Calculated by Moritz von Rohr on the scientific approach of the ophthalmologist Allvar Gullstrand, PUNKTAL lenses were the first axially symmetric spectacle lenses to reduce the blur at the edge of the lens. In 1935, the ZEISS physicist Alexander Smakula was granted a patent for a process that reduces reflections at lens surfaces, and ZEISS became the first company to bring such anti-reflective coatings to market. ZEISS called it the T coating, for "transparency". Anti-reflective coatings for spectacle lenses followed in 1959, and in 1974 ZEISS introduced a multi-layer coating for them. In 1969, cameras with ZEISS lenses took the photographs of the Apollo 11 Moon landing.

The problem: glare from behind

When the sun is low behind you, or bright light comes off a wall or a car beside you, some of it hits the back surface of your sunglasses. An uncoated lens surface reflects about 4% of the light that reaches it, and on the back surface that reflection goes straight into your eye. You see it as faint ghost images or a haze over what you are looking at.

The darker the tint, the more noticeable this is. A Category 2 lens lets through 18–43% of the light in front of you, while the reflection of the light behind you stays the same, so it makes up a larger share of what you see.

The solution: a back-surface anti-reflective coating

How it works

An anti-reflective coating is a stack of very thin layers, each with a different refractive index. Each layer is about a quarter of a wavelength of light thick. Light reflected from the top of a layer and light reflected from the bottom of it end up out of step and cancel out. This is called destructive interference. With several layers tuned to different wavelengths, the coating works across the visible spectrum.

The layers are applied in a vacuum chamber, where the coating material is vaporised and settles on the lens in a controlled thickness.

Why only the back

On our lenses, the anti-reflective coating sits on the inner surface only. That is where the reflections that reach your eye come from, so that is where the coating does its work.

The front surface stays uncoated on purpose. A front anti-reflective coating mainly changes what other people see, and it leaves a faint coloured reflection on the lens, usually green, in newer ZEISS coatings bluish. Leaving the front alone keeps the tint the colour it was designed to be.

DuraVision: protection against scratches

A scratch on a lens is more than a cosmetic flaw. It scatters light, and enough fine scratches turn into a haze across your vision.

Our lenses carry ZEISS DuraVision, a coating system that combines several layers:

ZEISS reports that one of its coatings is three times harder than its previous generation of hard-coated plastic lenses. A hard coating is not scratch-proof, though, and how you clean the lens still matters: rinse grit off before wiping, and use the cloth that comes with the frame. Our product care guide covers the details.

UV400: full UV protection in every tint

Every lens in our frames blocks 100% of UVA and UVB. The UV400 rating means it blocks all light up to 400 nanometres. The standard for clear spectacle lenses ends at 380 nm, yet around 40% of the UV that reaches the Earth lies between 380 and 400 nm, according to ZEISS. Since mid-2018, all current ZEISS-branded plastic lenses have come with UV protection up to 400 nm.

The UV filter is part of the lens material, not the tint. Switzerland's Federal Office of Public Health states that UV protection depends on the lens material, not its colour or tint, so our light Category 1 lenses block UV as fully as the darker ones. Our UV protection guide explains why darker lenses are not safer, and the lens categories guide covers which tint suits which light.

Frame and lens as one system

A lens only does its job if it stays in the right place in front of your eye. If the frame bends out of shape over time, the lens tilts or shifts, and you look through it at a slightly different angle than intended.

Our frames are made from beta-titanium, which springs back from everyday bending. Putting the frame on with one hand or a knock in a bag doesn't leave it bent, so the lens stays aligned. A hard enough bend can still leave it out of shape; an optician can adjust it. The frame weighs 16–18 g.

The ZEISS lenses come in several tints across the Archē range, all with the same coatings and UV400 protection:

NOUS NAVY

250,00 €

IRIS BRONZE

250,00 €

Conclusion

The ZEISS lenses in our frames do three jobs. The back-surface coating removes the glare from behind you, DuraVision keeps the surface clear, and UV400 blocks all UVA and UVB whatever the tint. The beta-titanium frame keeps all of that in the right place. Every pair of Archē sunglasses is fitted this way.

Frequently asked questions