Today we will see how a small party of lenses can change from a solid or liquid lens raw material to a crystal clear and photometrically accurate optical product.
In the eyewear industry, lenses that are customized according to specific parameters are generally known as Rx lenses and compared to mass-produced, one-off ready-made lenses, Rx custom lenses have more production processes, are more demanding, and are naturally more expensive. In a broader sense, Rx lenses include a series of lenses that require multiple processing through semi-finished substrates, such as progressive multifocal lenses, color-changing lenses, dyed lenses, etc.
In the narrower sense of Rx lenses, as opposed to stock lenses, when the refractive power of the consumer is rare, such as spherical lenses greater than ±12.00D or column lenses greater than -2.50D or -3.00D, the lens manufacturer does not have such unconventional power lenses on hand and needs to open and grind them according to the specific power, i.e., custom lenses. The range of availability of existing lenses can be up to 1200 degrees for some manufacturers, while some need to be custom-made if they exceed 800 degrees.
Both the ready-made lenses and the Rx lenses are processed from the basic semi-finished substrates, which are produced in the process of “transformation into magic.”
The production process of ordinary lenses
Different lens manufacturers, with different equipment and different quality management systems, may differ in the specific aspects and time points of lens production and processing, but their core processes are similar. The process of processing semi-finished substrates generally includes the following links.
configuration of raw materials for lenses → preparation and assembly of molds → casting of raw materials → curing → opening of molds → edge trimming and cleaning → curing again → inspection → hardening → inspection → three times curing → coating → inspection → packaging
Take the common resin lenses on the market today as an example, the raw material is in the form of liquid, and the largest proportion of the raw material is a polymeric monomer, such as the MR™ series produced by Mitsui Chemicals, which is a type of polymeric monomer. The monomer material is carefully blended with various additives such as hardeners and dyes (anti-blue light) and then injected into a lens mold made of glass, cast, molded, cured, opened, and cured and coated several times before becoming a lens.
In this process, the properties of the raw material, the precision of the mold, and the process are crucial.
*If the precision of the mold is inaccurate and defective, it may lead to the production of lenses with inaccurate luminosity.
* Poor control of temperature or duration in each step may lead to poor physical properties and even deformation of the finished lenses.
*Poor physical properties of the raw materials of the lenses may lead to internal stress in the finished lenses or poor adhesion of the film layer, which may lead to bad phenomena such as film peeling and lens discoloration in use.
The production process of Rx lenses
After the previous steps, a substrate with accurate luminosity and shape is completed, and after hardening, coating, and quality control, it is ready to be labeled and sold in the factory. However, there are more processes to be carried out in the Rx lab.
After receiving the personalized fitting data from the consumer, the retail terminal transmits the order data to the Rx lab, which, through built-in software calculations, converts the parameters into data that is stored in the system and selects a suitable semi-finished substrate from the inventory for further processing.
Then comes the most critical part of the workshop processing, which is to process the detailed photometric parameters onto the substrate that already has a certain luminosity. This process includes grinding, polishing, etching, etc. The requirements for precision are very high and are usually achieved through precision automated CNC machines. The technical strength of each manufacturer is reflected in the calculation, modeling, and optimization of the customer’s personalized data, as well as in the precision of the CNC machines. After cutting and grinding, the lenses change from semi-finished substrates to progressive multifocal lenses with various functions, anti-fatigue lenses, special luminosity lenses, etc.
Subsequently, the Rx lenses also go through similar cleaning, hardening, coating, and quality control processes as normal lenses before finally becoming a qualified lens that is delivered to the consumer. This also explains why prescription eyeglass lenses are so expensive; of course, these prices in the opticians include layers of wholesalers’ profits, while the internet sales prices without the intermediaries’ markups are a bit cheaper. The same quality as cheap glasses, now you know how to choose them!
Although the lens is small, its technological content is not less, between the millimeter of light control, smooth and free curvature change, all contain generations of industry wisdom crystallization, mastering the knowledge of lens production, allowing practitioners to value the beauty of technology, but also to better communicate the value of lenses to consumers.