The Making of a lens
The making of 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 professionals and advanced amateur photographers or is the lens targeted for use by the general consumer? This criterion 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.
Once the target market is determined it then becomes a matter of determining:
- Optical design approach
- Materials to be used (both optical and mechanical)
- How to process the mechanical components, i.e. by machining or by molding
- What type of AF interface to be employed in the case of auto focus lenses
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 manufacturing 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 professionals or consumers.
Computer simulations for effective production preparation
Once the optical design is completed, a computer simulation delivers a precise prognosis about the end performance of the lens at the image centre and at 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.
Pioneering developments in mechanical design
While the optical designers meet the challenges of optical performance, the mechanical designers work 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 be durable to withstand long periods of use under changing environments.
Quite often as the optical design becomes 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 usedin order to mass produce this lens. In the meantime, a further technical advancement was achieved with the "Quad Cam" used in the 28-300mm.
Prototypes for extensive practice tests
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 includes shooting a target chart in the lab as well as field testing under different light conditions, i.e. towards the sun; against the sun; in the shade, etc.
The proto-type samples are then tested under varying temperature and environmental conditions to see how these factors may potentially affect the lens performance (focusing ring, zooming ring, diaphragm blade movements). In addition the lenses are subjected to an accelerated aging test in a lab to ensure durability. The optical and mechanical engineers use the results of all of these tests for the final perfection of the design.
The auto focus is designed
Concurrent to the finalization of the optical and mechanical design, the auto focus design is initiated. 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 „breadboard" 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. The result is a customized micro-chip (normally a ROM) that actuates the auto focus and is incorporated as a part of the mechanical construction.
The preparation for serial production
When the overall 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". Here the rough contour of the element is shaped which is either concave or convex.
As the grinding progresses and the elements are shaped closer to their 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 AD (Anomalous Dispersion) glass require a longer processing duration due to the softness, fragility and oxidization of the materials. This explains the relatively high cost of lenses using LD or AD glass which is not only attributable to these factors but also to the higher initial cost of these materials. The higher price for these materials is justified, in any case, because the use of such high tech glass materials effectively reduces chromatic aberration.
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 is evenly ground to the optical axis. Another type of optical element used in the production of lenses is called "Hybrid Aspherics" which is used to compensate spherical aberration, a form of optical noise resulting when light rays are broken by spherical elements and do not focus at the same point on the image plane. This loss of image quality can be eliminated to a great extent by means of aspherical elements (meaning elements which cannot be derived from a spherical form). The use of aspherical elements also effectively reduces the image distortion of a lens.
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.
The coating – ultra thin layers with a huge effect
After the elements are formed, the next stage is the coating process. This is one of the critical factors in lens production for which each company has developed its own proprietary technique. Coatings on the lens element serve the purpose of protecting the element itself from oxidization and preventing unwanted reflection.
Reflections not only reduce the light transmission of a lens (in every lens surface apx. 4% of the light is lost due to reflection), they are also largely responsible for decreased image contrast, diminishing the image quality of a lens considerably.
A multiple-layer coating technique is applied for optimum color rendition and maximum light transmission. In the meantime, Tamron has developed new "Internal Surface Coatings" (i.e., multiple-layer coatings on cemented surfaces of plural elements) to further reduce reflections and guarantee a higher image quality.
The mechanical parts
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 manufactured 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 plastics 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 manufacturing of the parts is completed the lens is 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, and 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 the designed standards. Inspections involve mechanical movement, optical resolution, auto focus response etc. Depending on the particular lens, it may then also be subjected to vibration and shock and/or drop tests.
Serial production begins after all final tests and tunings, and the lens is introduced into the market. Controls and tests also continue during serial production, in order to ensure that the high quality standards as per the ISO 9001 certification are met.
In addition, all production processes at Tamron are examined for their environmental compatibility and constantly optimized. Tamron has fulfilled its environmental commitment for years and actively promotes measures to protect the environment within the company, conforming to the strict requirements of ISO 14001.