These days, the production process for eyeglass lenses is largely automated. Once the ECP has sent the patient's lens order to ZEISS, the first production step begins: the individualized lens is calculated and the data required for manufacturing the lenses is made available. Each production order is assigned a bar code so that the data necessary for processing the lens can be identified at each station in real time and then loaded to the particular processing station.
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Depending on the prescription, the semi-finished lenses are selected automatically in the warehouse. The semi-finished lenses for the left and right eye already have an optical power on the front surface. To create the wearer's prescription, only the back surface is machined with ZEISS freeform technology. The semi-finished lenses – also known as "pucks" because of their shape – are automatically taken from the warehouse and placed in a tray. Then the journey begins: conveyor belts transport the tray from one station to the next until ultimately two eyeglass lenses have been created.
Once blocking is complete, the lens is formed to give it the desired shape and prescription. With ZEISS freeform technology, the front surface of the semi-finished lens already has the corrective optical power when taken from the warehouse. Only the back surface still needs to be machined and shaped for the particular wearer. To do this, a 5-axis CNC method is used that creates the right shape and prescription for the wearer in around 90 seconds. Basically, three different steps are performed within a minute and a half: the lenses are roughened, given a general shape and then tens of thousands machining points are defined using a natural diamond. This method enables the manufacturer to freely customize the optical surface, i.e. freeform.
During polishing, the surface of each lenses is polished while the optical properties remain unchanged. A perfect surface is important for the application of modern lens coatings that do not separate from the lens. Every ZEISS lens gets its own special signature: a laser is used to engrave a nearly invisible "Z" in the lens. This precisely positioned marking is important for quality assurance and affixing a stamp that later assists with grinding and centring the lenses.
Now the lens is de-blocked, i.e. carefully removed from the blocker. Since the metal alloy connecting the lens to the blocker melts at just under 50° C, it is simply dipped into hot water. The lens is then cleaned much like a car at the car wash: brushes, different cleaning agents and ultra-pure (i.e. especially well-treated) water are used to remove any traces from the lenses and prepare them for coating. The lenses are then blow-dried. Environmental protection is a matter of course at all production facilities: materials like the metal alloy are treated and reused, and the water required for production is recycled in an environmentally friendly manner.
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At this stage, the lenses are tinted if requested. Plastic lenses are placed in a dip dye batch, while glass lens tints are applied in metal oxide layers.
Textile colors that do not pose any risk to human health or the environment are used for plastic lenses. This process requires great dexterity: since each lens is manufactured individually and ZEISS offers tints in any color, a lot of experience is necessary to achieve the "right" tint.
Now comes the final step in the production process, which is the most demanding technologically: the application of a lens coating. Coatings make the lens scratch-resistant and durable, help ensure crystal clear vision when it's windy or in inclement weather, repel dirt, reduce irritating reflections and offer many functional benefits, such as when a person is driving or working at the computer. Unlike their glass counterparts, plastic lenses are not adequately scratch resistant on their own. Thus a suitable hard coating to protect against scratches is always a must for ZEISS plastic lenses. This is applied as a lacquer to the plastic lens in the dipping process, hardening it. Which of the various specially customized lacquers are used depends on the plastic and thickness of the lens. After ultrasonic cleaning, the next coating is added by applying anti-reflective layers in a vacuum deposition process – and we do mean layers, because a modern lens can have up to nine. The final layer of coating gives the lens its extremely smooth surface, making it particularly resistant to both dirt and water.
The lenses are almost done. But do they meet ZEISS' strict quality assurance requirements? To ensure they do, each lens is thoroughly inspected before delivery. A visual inspection is performed to check for dust or damage, as well as a mechanical one to ensure that each lens meets the necessary specifications. Are the diopters, the axis, cylinder, thickness, design and diameter correct? If the lens is flawless, then it is "stamped" in the final step. This orientation stamp is used to align the lens and assists the ECP with inserting it into the frames precisely. It is removed before the final pair of glasses is dispensed to the wearer.
The Z for ZEISS is only engraved once all the quality assurance steps have been successfully completed and the lens really does feature ZEISS quality. The Z is our signature – our quality promise inscribed into every individual lens.
And anyone who wants a unique label in the eyeglass lens can have their initials engraved!
Fun fact: did you know that only women work in the ZEISS tinting department? The reason: women tend to have better color vision than men, making them extremely good at identifying slight deviations from the norm.
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