With a 20-year history since its establishment, the Tamron plant in Foshan has now achieved a level of growth that puts it almost on a par with the three mother plants in Aomori, as I mentioned in the previous blog.
   Although the Foshan plant still relies on the mother plants for the production of some key parts and some processing (e.g. metal molds, aspherical GM lens elements and nano-structured lens coating), it performs plastic molding using metal molds, the precision machining of metal parts, lens polishing, the sub-assembly of electronic components, and the main assembly of interchangeable lenses, and it ships the products directly to markets around the world.

   The assembly of interchangeable lenses (sub-assembly and main assembly) comprises very important processes that directly affect the finish quality of the products. I would like to draw your attention to the fact that merely assembling and anchoring parts as instructed is not sufficient for finishing the products as intended by Tamron. It is somewhat different from building plastic models as a hobby.
   Sub-assembly is also referred to as a sub-process, and it is about creating modules and units by assembling relatively small parts in advance. Main assembly comprises the main processes for assembling lenses by combining the sub-assembled modules and units as specified to create complete products.

   A key point regarding lens assembly is that in the process of assembling a lens (main assembly), inspections (checks) are repeatedly conducted, and readjustments are made as and when they are deemed necessary. At times, the lens element groups that have been combined are disassembled, and after careful adjustments, they are assembled once again. There are a lot of work procedures that it is not possible to make light of in any way when aiming for outstanding quality and performance.

   Please first take a look at the flowchart below, which shows a broad outline of the assembly processes and their flows for interchangeable lenses.
 

   In the sub-processes (sub-assembly), the optical lens elements with polishing completed are assembled as individual lens element groups, the small electronic parts are assembled to create AF and VC units, and aperture control mechanisms are combined as units, thus creating the mechanism components that make up an interchangeable lens.
   Gathering a number of the necessary components that have been fabricated in advance, the main assembly for producing a complete interchangeable lens finally begins. This marks the start of the main processes for creating each interchangeable lens.

   I would like to provide a simple explanation here of the order of the assembly work carried out in the main processes.
   Many of the interchangeable lenses are assembled according to the following procedures. Specifically, these are examples for two zoom lens models, the 16-300mm F/3.5-6.3 Di II VC PZD MACRO (Model B016) and the SP 24-70mm F/2.8 Di VC USD (Model A007), which were being assembled in the main processes during my tour of the Tamron plant in Foshan. Quickly skimming the following flow will be sufficient, so please take a look at these procedures.

   ①Installation of the lens element groups (fitting each lens element group into the basic outer barrel of the lens, and provisionally fixing each group in its position)
   ②Installation of the aperture unit (forming a set with the lens element groups)
   ③Installation of the VC unit (forming a set with the lens element groups)
   ④Installation of the flexible printed circuit boards
   ⑤Installation of the zoom ring and focusing ring
   ⑥Installation of the piezo drive (PZD) or ultrasonic motor drive (USD) unit
   ⑦Installation of the main circuit board (circular substrate) in the rear area
   ⑧Installation of the rearmost part of the lens barrel
   ⑨Installation of the selector switch for the AF and VC systems
   ⑩Installation of the mount
 

   Processes (i) to (x) above comprise the assembly of an interchangeable lens (zoom lens), and the final form of an interchangeable lens is more or less created as a result. Actually, though, what can be described as the key stage or the real deal of the whole main assembly processes starts right here; these are the processes of inspections and adjustments.
   These processes consisting of the inspections and adjustments are, in fact, the most important processes in creating a lens of outstanding quality. Each inspection and adjustment is a sophisticated process requiring delicate care and precision. There are many processes in which the inspections and adjustments are carried out using dedicated instruments, many of which are developed for use by Tamron itself, as is the case for other manufacturers. What follows is a broad outline of the inspection and adjustment processes.

   ①Flange focal distance adjustment: Adjusting the flange focal distance (the distance from the mount surface to the sensor plane) to enable accurate focusing to infinity.
   ②Optical axis adjustment: Also called “centering,” this is a vitally important adjustment process. An inspection is undertaken as to whether the center of each assembled lens element group is accurately aligned with one optical axis. If tilted and misaligned, it could cause one-sided blurring, so accurate realignment is required.
   ③MTF testing and adjustment: Generally, conducting an inspection using a dedicated MTF tester. Reading the memo stating the span of the adjustable range, removing the lens element group and adding washers, etc. for adjustment. This is also a very important process.
   ④VC adjustment, AF adjustment: Conducting inspections as to whether the vibration compensation (VC) and AF mechanisms operate according to the standards, and making fine adjustments if necessary.
   ⑤Inspection by attachment to a camera: Attaching the lens to a compatible camera body, performing basic operations, and checking whether there are any problems.
   ━━ After this inspection, installing the zoom ring rubber and the brand ring to complete the external appearance.
   ⑥ Focus torque and zoom torque inspections: Carefully checking the operational feel of the focus ring in MF mode, and performing zooming to check the rotary torque and ascertain whether there is an awkward feel. These are inspections of a sensory nature that should be conducted by veteran workers with a wealth of experience.
   ⑦Inspection of the inside and appearance inspection: The final inspection, with a thorough visual inspection conducted to check for any dirt, etc. inside the lens and assess the external appearance.
   ━━ After the inspections and adjustments outlined above, the completed product is now mostly ready. Once the serial number is stamped and the lens cap and lens hood are mounted, the product moves on to the packing process.
 

   I have provided explanations of the assembly, inspections and adjustments conducted in the main processes, but in fact, more elaborate inspection and adjustment processes are performed as well. For each task carried out (whether for the assembly process or the inspection process), an air duster is used to carefully remove any dust or dirt, only after which the product is moved on to the next process. Naturally, the work sections for assembly and inspections are in a clean room environment.
   Observing such meticulous work at the Tamron plant in Foshan, there were a number of times when I was really impressed and couldn’t help but think: “Wow, you do go to great lengths!”

   I understand that the assembly and inspection processes are conducted in exactly the same ways as at the Hirosaki plant in Aomori, Japan, with their methods and systems fully applied to the Tamron plant in Foshan. The thorough quality control and the measures for ensuring performance without fail are carried out to reliably provide customers with each lens bearing the Tamron brand name, regardless of where it was made.
   This is why all Tamron lens products have exactly the same quality and performance, wherever they are manufactured.

   I hope you will look forward to the next blog, where I will introduce some of the people engaged in lens manufacturing at Tamron’s Foshan plant as we take another fresh look at how the lenses are made.