Learning Center
Lens Making

Making a lens involves numerous steps, the first of which is the basic design. Determining the target users for any lens is the starting point in the basic design approach. Will the lens be used by working professional and advanced amateur photographers or is the lens targeted for use by the general consumer? This criteria defines the level of performance necessary in various categories: optical performance; durability factors based on usage; and environmental changes due to typical areas where used.

In approaching the optical design, there are certain basic patterns in lens design technique that have been established as a sort of "template" for conventional lens design separated by category of wide-angle, telephoto, and macro.

However, lens designers face a lot more challenges today due to the advancements made in the manufacture of the materials used in the lenses which range from the optical glass itself; metal component materials; to plastic materials and the processing method of these materials. While these new materials provide lens designers with greater choices and freedom of design in their quest to make a superior product, they also face market pressures which demand cost reduction. The optimum goal is to make a better lens at a lower cost, whether the product is designated for pro's or consumers.

Once the optical design is completed, today's computer programs allow simulation of the end-result performance at the image center and the corners. It should be noted that lens manufacturers have made their own technological advances and use their own design and manufacturing techniques developed from their experience. This includes the computer programs which are generally developed by individual companies and are therefore proprietary.

At this stage, it is determined whether the lens will meet the initially targeted performance criteria. If there are any potential problems indicated, the optical design is altered.

While the optical designers are meeting the challenges of optical performance, the mechanical designers are working on making the optical design usable for photographers. The movement of each optical element must be fully functional and error-free and it has to durable to withstand long periods of use under changing environments.

Quite often as the optical design become very sophisticated, the mechanical design must exceed that sophistication, breaking through conventional design practices to a new methodology that sets a higher standard. Tamron's "Triple Cam Design" is a perfect example of this breakthrough design approach.

The "Triple Cam Design" is employed in the 28-200mm F/3.8-5.6 Aspherical zoom lens which has won numerous awards for its innovative design and excellent cost/performance ratio. This lens would never have been brought to market without the creation of this new mechanical design and invention of the processing method used to be able to mass produce this lens.

Once the mechanical design is completed, several proto- type samples are made in order to evaluate the lens performance in various conditions from favorable to adverse, and to evaluate the feasibility of actually producing the lens in quantity. Resolution, contrast, and color rendition are carefully tested at every aperture position from wide open to the minimum and at every focal length, in the case of a zoom lens. This process is done in a lab shooting a target chart and also in the field under different light conditions, i.e. to the sun; against the sun; in shadow, etc.

Then the proto-type samples are tested under varying temperature and environmental conditions to see how these factors may potentially affect the lens behavior (focusing ring, zooming ring, diaphragm blade movements). Sometimes the lenses are subjected to an accelerated aging test in a lab to ensure durability. The results of all of these tests are given to the optical and mechanical engineers for final perfection of the design.

Concurrent to the finalization of the optical and mechanical design, the auto focus design is initiated for the AF lenses. In order to ensure total compatibility and functional ability of the lens with each camera manufacturer's camera body, a great deal of software development must be utilized at this stage. Once a"bread-board" of the AF module is made, it is loaded into the proto-type lens to test the practical functional ability and the fine-tuning process of the software in conjunction with the mechanical design takes place. This results in the production of a customized chip (normally a ROM) that can be incorporated as a part of the mechanical construction.

When the total lens design is finalized, the manufacturing process begins. There are many parts to the process which culminate in the finished product. The optical glass materials used in lenses are available from a few manufacturers and quite often these companies supply the glass in the form of a "pressed plate", a sort of sliced glass plate. The glass elements are then sent through the initial grinding process using a machine called a "curve generator". This creates the rough contour of the element either concave or convex.

As the grinding progresses and the elements are shaped closer to the final specifications, the polishing particles contained in the water to process the element surface get finer and finer toward the final stage. The speed of the curve generation and grinding can vary depending on the characteristics of the glass material itself and the diameter and contour of the lens element. Materials typically called LD (Low Dispersion) or ED (Extraordinary Dispersion) glass require a longer processing duration due to the softness, fragility and oxidization of the materials. Naturally, the relative high cost of lenses using LD or ED glass can be mainly attributable to these factors and the initially higher cost of these materials.

Once the final polishing is done, the elements go through a centering process, which ensures perfect eccentricity of the individual elements. In other words, the circumference part of the elements are evenly ground to the optical axis.

Another type of lens element used in lenses is the result of a technology developed by several companies called "Hybrid Aspherics". This is a compound method of bonding glass and resin materials to produce a lens element with a non-spherical surface. The formation of the aspherical surface onto the completed element is accomplished through the centering process.

After the elements are formed, the next stage is the coating process. This is one of the critical factors in lens production and each company has developed its own proprietary technique. Coatings on the lens element serve the purpose of protection of the element itself from oxidization and prevention of unwanted reflection while providing designed spectrum transmission to ensure optimum color balance. Sometimes several layers of coating are applied for optimum color rendition and maximum light transmission.

The barrel components and cosmetic parts are produced by a die cast method and/or machining process. Parts with carn grooves and helicoid are some of the most critical components of all since their accuracy largely influences the final quality and performance of the lens. Today, more and more of
these parts are manufacturer by an engineering plastic, ultra-high precision injection mold technique that yields high production efficiency. Needless to say, the lens chassis components produced by engineering plastic allow the lens to be very lightweight.

Internal surfaces of the lens barrel are carefully and thoroughly treated to provide a non-reflecting surface. this is also a critical process to reduce flare which tends to be caused by stray light bounced back and forth inside the lens barrel.

When the parts manufacture is completed the lens is the assembled. Several key components such as the diaphragm mechanism are made as sub-assemblies for production efficiency and to ensure accuracy to the design specifications. The whole mechanical structure of the lens is assembled together, then the elements are placed in position.

After the final assembly, various adjustments take place to make sure all the functions of the lens meet with the designed standards. Inspections involve mechanical movement, optical resolution, autofocus response (in the case of AF lenses), etc. Depending on the particular lens, it may then also be subjected to vibration and shock and/or drop tests.