How is a spectacle lens actually made at Wetzlich? It is a long and complex production process before the lens gets fitted into the frame. What materials are used to make spectacle lenses and what steps are involved in the production of spectacle lenses? We have summarized all this and the special features of lens production at Wetzlich here.
Have you ever wondered how a spectacle lens gets actually produced? The production of spectacle lenses is a precise and technically demanding process. In fact, many complex production steps are required from the eye test to the finished spectacle lens. And one thing is quite clear: not all lenses are the same. Precision and individuality are required in lens production!
Depending on whether plastic or mineral glass is used for the lens material and whether they are used as standardised stock lenses or individually manufactured lenses (prescription lenses), different processing methods are used.
However, the raw material for lenses is always organic plastic or mineral glass.
As part of the lens production process, the lens blanks undergo various manufacturing steps, from shaping and grinding to surface finishing.
Blank: Designation for lens blanks at the start of production, but also for semi-finished products.
Organic Material: Plastic lens material. Nowadays it is used almost exclusively for manufacturing of lenses.
Mineral Glass: Mineral glass is harder, but also heavier than plastic.
Stock Lenses: Stock lenses undergo a different manufacturing process and are more recommended for minor visual impairments as they cannot be individually adapted to the wearer.
RX Lenses: Individual, custom-made lenses according to the wearer’s individual parameters.
Lens production is technically demanding and requires a high degree of precision. Here you can gain an insight into Wetzlich lens production. We describe the individual steps from the lens blank to the individually manufactured lens in your spectacles.
Precise processing of the lens requires equally precise preparation. For this purpose, a so-called “block piece” is applied to the front of the lenses, on which they are fixed during the rest of the production process. We work sustainably with a reusable block piece and simply glue it onto the blank (lens blank).
In the so-called “generator” for surface treatment, the previously calculated three-dimensional surface is transferred to the blank. First, the excess material is roughly milled off, followed by high-precision machining with a diamond milling head. After this process, the surface is polished. Of course, this process produces plastic waste – unlike other lens manufacturers, Wetzlich pays attention to environmentally friendly production here. This is why it is a particular challenge for us to separate this waste from the grinding water and then utilize it.
Lens polishing is a significant step in the lens manufacturing process that has a major impact on the optical quality and comfort of the glasses. The main aim of polishing is to make the surface of the lens as smooth as possible. This reduces stray light and improves the clarity and quality of the images seen through the lens. A well-polished lens enables more precise refraction of light and therefore improves visual acuity.
Laser engraving is a modern process used in ophthalmic lens production to apply permanent markings to lenses. This technology offers numerous advantages, for example, the traceability of the lenses. The laser machine uses high-precision lasers to create micro-engravings on the surface of the lenses. The laser beam is so finely adjusted that it can precisely ablate the surface of the lens without impairing its optical properties.
Laser engraving is usually carried out after polishing and before the application of coatings. The glass is positioned under the laser and the specific data is entered under program control to create the desired marking.
Lens cleaning is a crucial step in production that takes place immediately after the blocking, grinding and polishing processes. This phase is essential to ensure that the lenses are free of any impurities, grinding residues or adhesives before they are subjected to further treatments such as the application of coatings.
When manufacturing lenses, precision and individuality are of paramount importance to ensure that the lenses have the required optical properties and the right fit. But the customer’s needs and visual requirements should also be taken into account during production and development. Our custom-made lenses are not only manufactured to the highest quality standards, but are also individually tailored to your requirements. We offer an individual solution for every visual requirement – experience the difference that high-quality lenses can make.
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Brown, grey, green, blue – each colour has its own advantages in sunglasses. But how exactly does the colour end up on the lenses? Sunglasses or lenses with a slight tint get their colour through a dipping process. A colour gradient is created, for example, by constantly dipping and re-dipping the lenses automatically. As always, precision is crucial here.
A particular challenge here is that the downstream processes can still have an influence on the colour in some cases.
Plastic lenses are a huge relief for spectacle wearers in the truest sense of the word and offer even more advantages. However, plastic lenses are obviously much softer on the surface than mineral lenses. To compensate for this disadvantage, all plastic lenses are given a so-called hard coating. This is usually applied in an immersion process and then cured in ovens. A special feature of these is that there is a separate hard coating for each material, depending on its refractive index.
During the anti-reflective process, a large number of wafer-thin layers are applied to the lenses, which are responsible for both the anti-reflective properties of the lenses and the beading effect of the surface. For this purpose, materials are “vapor-deposited” onto the lenses in a high vacuum.
While the cosmetic surface inspection is still carried out manually, all technical parameters of the lenses are checked fully automatically. For example, the thickness of the lenses is measured, the values are checked with high precision at the measuring points defined in the DIN standard, the entire surface of the lenses is checked and, as can be seen here in the picture, stamps are applied to the lenses, which serve as a guide for the optician to fit the lenses into the frame.
As this is a medical product, the packaging is of course of particular importance. All the relevant parameters of the jar are once again recorded on it. The lense envelope also serves to protect the product during shipping. As with all outer packaging, we now work exclusively with paper to avoid generating unnecessary plastic waste.
Spectacle lenses can be made from two main types of material: Glass and plastic.
Glass lenses are made from optical glass, which is known for its clarity, scratch resistance and excellent optical properties.
Plastic lenses are made from different types of resins, including polycarbonate and CR-39 (a plastic polymer), which are lighter than glass and offer high impact resistance. High-index plastics are also used to provide thinner and lighter lenses for higher prescription values.
Want to opt for environmentally friendly lenses? EVA (Ecologival Value Added) is a plant-based lens material and offers the wearer a great alternative to help protect the environment and the climate.
Which lens index (1.50 to 1.74, incl. Poly/Trivex) is suitable for which requirement?
Basically, plastic materials can be divided into two different material groups. Trivex and polycarbonate as so-called thermoplastics (fusible) differ from the other materials (thermosets – hardened by heat) due to their excellent resistance to breakage. It is not without reason that these materials have always been used in all areas of occupational safety, in sports applications and also in military applications. In addition to these properties, thermoplastics are particularly lightweight. For the end consumer, Trivex and polycarbonate are the first choice for children’s glasses and sports glasses. However, polycarbonate in particular also has a few disadvantageous properties. For example, polycarbonate is not the best choice in terms of optical imaging and is quite susceptible to some cleaning agents.
So there are also good reasons for the market-dominating thermosets, under which the standard indices 1.50, 1.60, 1.67 and 1.74 are summarized. A decisive advantage of these is that it is possible to produce significantly higher indices = thinner lenses. The higher indices in particular also score points for the natural UV protection of the materials without the need for tinting.
The question: “What is the best material?” is therefore not easy to answer.
For sports applications, we recommend Trivex and polycarbonate. For normal everyday use, the decision is usually based on visual acuity. The now obsolete CR39 material in index 1.50 is no longer recommended for many reasons (UV protection, break resistance, processing properties, thickness). Index 1.60 is becoming increasingly established as the standard, which is upgraded to index 1.67 or 1.74 depending on the wearer’s dioptrical powers.
The time it takes to manufacture lenses can vary depending on the complexity of the lens recipe and specific requirements such as coatings or customization.
In a perfect world, where only one lens would go through the entire production process, the production process can be roughly summarized as follows:
In short: approx. 10 hours
Unfortunately, in reality it is not quite so simple, as there are different machine utilization rates, different lacquers, different anti-reflective coatings, various intermediate checks that may lead to new runs, etc. The longest waiting times regularly occur with anti-reflective coating because this is always carried out in so-called tours – i.e. glasses with identical coatings are collected and combined in one tour. Efficiency and, not least, environmental protection issues also play a role here, as these are very energy-intensive processes and it is neither economically nor ecologically justifiable to run a single pair of lenses in a tour that is actually intended for 140 lenses.
Realistically, you should therefore expect a processing time of approx. 4 days for normal lenses.
The main difference between plastic and glass lenses lies in their weight, break resistance and optical properties:
In short, plastic lenses are simply much lighter and do not have the disadvantage of becoming denser (=heavier) as the index increases (thinner lenses) due to the material additives.
Due to these many advantages, they have gradually almost replaced mineral lenses on the market. Mineral lenses therefore have a niche existence in occupational safety in the chemical industry (because plastics rarely like solvents) and occasionally in very dusty environments, because no matter how much you try to sugarcoat it: Modern plastic lenses with high-tech coatings do not like having dust rubbed off them dry every day.
We have been manufacturing lenses with the highest precision and innovative strength in Germany since 1935.
We not only ensure that you simply see better and more with our products. For years we have been developing lenses that provide optimum protection for your eyes. This includes e. g. our UV and infrared protection coating as well as innovative lens materials that filter blue light and increase contrasts.
With one of the most modern European machine setups, we stand for advanced products with the highest quality standards at fair prices.
You can purchase WETZLICH lenses from your local optician. Simply ask him about our lenses or find a WETZLICH partner optician in our optician search.
