It is naturally very important to create an interchangeable lens with superb depictive quality and excellent optical design and technologies. As a result, optical designers tend to be in the spotlight frequently, and there seems to be an impression that optical designers are THE key persons who have a definitive influence on whether or not a lens turns out to be an excellent product.
   But when we think about the interchangeable lenses we use, it is clear that merely ensuring a superior optical design is not sufficient.

   While high-level technologies for grinding and polishing lens elements just as specified in the drawings of optical designers are certainly important, we should not overlook the importance of the design work for the lens barrel (main barrel, lens frame), which allows for the smooth movement of the optical lens element groups while holding them firmly.
   In addition, unless excellence is ensured for the AF and VC (vibration compensation) systems, the electronic components, and the software programs controlling them, it is not possible to say that it is a good interchangeable lens.

   Regarding each of the latest interchangeable lenses, the AF unit, VC unit, aperture unit, and the IC and the electronic substrates for controlling them are squeezed into a very narrow space. It is necessary to place important units and components as well as lens element groups inside the lens barrel in a compact, efficient configuration.
   Designing the lens barrel (main barrel) by paying careful attention to the minute details is needed here, planning the individual parts and their shapes so that the installed parts never become loose or come off, while ensuring smooth movements.

   At Tamron, the divisions in charge of mechanism design are responsible for the overall design of these mechanisms and configurations. At other manufacturers, labels such as “frame design” or “mechanical design” may be used for the departments in charge.
   In this article, I would like to shed some light on several areas of the mechanism design work carried out at Tamron. (I may provide more in-depth explanations of Tamron’s electronic design for AF and VC, etc. another time if there is an opportunity.)
 

   A mechanism designer is at times told by the engineers in charge of the design of electronic components, “There is no longer enough space to incorporate the necessary parts,” and receives demands from optical designers such as, “Please devise a mechanism to enable this lens element group to smoothly move at high speed.” Trying to accommodate these requests and also racking their brains with regard to the processing cost and the parts cost, a mechanism designer keeps moving forward valiantly with the design process.
   You should also not discount the personnel in charge of assembling the lens at the plant. They may at times demand something like, “Please change this to a design that allows for easier assembly,” as a result of which the mechanism designer has no choice but to make a design change.

   Proceeding with the design while listening to these demands and requests from various divisions, making adjustments and promoting coordination (and also sometimes humbly asking for cooperation and help) is the work and life of a mechanism designer. I suspect that their division is maybe the one that has to go through the most hardships among all the divisions of interchangeable lens designers. In fact, while using interchangeable lenses, I often feel like this: “Hey, the mechanism designers must have really put a lot of effort into creating this particular lens!”

   When focusing or zooming, the lens element groups move to and fro inside an interchangeable lens, and achieving perfectly smooth movements for them through design is an area where mechanism designers can truly show their skills and expertise. (Autofocusing at high speed is required, so nowadays, small lens element groups move forward and backward driven by a motor.)
   For both zooming and focusing, most interchangeable lenses now adopt a method of rotating the barrel area, including the focusing ring and the zoom ring. Inside the lens, multiple optical lens element groups move to and fro, so this requires a mechanism for converting the rotational movements into linear movements, with smooth, rapid movements a must.
   A drive mechanism called the “cam groove” is in place to do this job.
 

   Narrow grooves are cut in a cylindrical lens barrel, and with cam pins moving along these grooves, the multi-layered barrel moves to and fro. In addition, the lens groups do not necessarily make uniform movements forward and backward. Sometimes, a certain lens element group moves forward slowly, and simultaneously, another lens element group moves in the opposite direction at a rapid pace.
   In the case of a zoom lens and for the floating system of the SP 35mm F/1.8 Di VC USD (ModelF012) as already explained in blog No.3 of this series, the lens element groups move in very complex ways. This means that the design of the cam grooves and whether really precise machining is performed to complete the parts will largely determine the level of operability when focusing and zooming.

   To create a lens barrel with cam grooves, either a frame made of plastic molding or a metal frame made of aluminum is usually used. The advantages of a frame made of plastic molding include the fact that mass production is possible at a lower cost. While the benefits of a metal frame made of aluminum include greater durability and smoother cam movements, it takes more time and labor to produce one.
   Excluding some less expensive lens products, Tamron has consistently continued using a metal frame made of aluminum for its lens barrels, showing Tamron’s commitment to not compromising on quality.
   While aluminum is a light metal, it is naturally heavier than plastic. Compared to a frame made of plastic molding, which can easily be produced through injection molding, it takes a great deal of time and cost and advanced technical capabilities to undertake cam grooving in the case of a metal frame made of aluminum.

   Some manufacturers use metal for the lens exterior that is touched by the customer’s hands, while using plastic molding for the inner barrel. But Tamron goes the opposite way, using a metal barrel inside where it cannot be seen by prioritizing precision and strength, while using plastic molding on the lens exterior by placing priority on weight reduction.
   If you look again at the photo showing the lens cross sections (photo-01 above), the areas that look white in the barrel are the metal frames made of aluminum, while those that look black are the frames made of plastic molding. Many of Tamron’s interchangeable lenses are the results of such dedication to quality and attention to the fine details.
 

   Tamron has been a pioneer of high-power zoom lenses. A high-power zoom lens requires a lot of movements for zooming, with the lens element groups moving in complicated ways. Zooming from the wide angle end to the telephoto end changes the overall lens length, with the weight balance of the lens also shifting considerably.
   Despite this, careful attention to detail enables very smooth zooming. Another aspect of Tamron’s zoom lenses to which I would like to draw your attention is that there are now very few lenses with any downward movement under the lens’ own weight.
   In the past, when you pointed a zoom lens upward or downward while shooting, this led to unintended zooming in some cases because of the lens’ own weight. But nowadays, you rarely, if ever, experience this with Tamron’s zoom lenses. This must be thanks to a lot of hard work on the part of their mechanism designers.

   Along with the design of the cam grooves, another very important factor is lens assembly. Whether a screw is fastened with the right amount of tightening in a subtle way and whether operation checks after assembly are performed with careful attention actually count for a lot. To ensure a smooth operational feeling without fail when zooming and to prevent any unintended downward movement under its own weight, it is important to pay attention to the smallest details and make fine adjustments.
   Whether careful work is performed with attention to detail in lens assembly basically determines the actual quality of the lens.

   In my next blog, I would like to provide explanations of various aspects of the grinding and polishing of each optical lens, which is a very important area for an interchangeable lens. Please look forward to our adventure as we gradually move into the actual Tamron plant.