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Yamagata: a long way from Osaka

The city of Tend? sits on a wide plain in the Yamagata prefecture of North Eastern Japan. It’s a city of just 61,000 people and, with snow-topped peaks visible in nearly every direction, feels even more distant from Panasonic’s headquarters in industrial Osaka than the 600km (370 miles) that actually separate them.

But this quiet spot, hemmed-in by the Iide, ?u and Asahi mountain ranges, plays an essential role in the company’s camera business, as it’s home to Panasonic’s Yamagata lens factory.

It makes other things, too, but we visited because it’s responsible for lens units for compact cameras, interchangeable lenses, and lens elements for both Panasonic and other (un-named) customers. The factory was founded in 1982 and has been making lenses since 1987, giving it 35 years of experience in the field. But, the company maintains, it’s still constantly looking for ways to improve.

All of the images in this article were supplied by Panasonic and are used with permission.

All the usual processes

The factory can take rough glass blanks or the raw materials for plastic elements in at one end and do all the processing and assembly needed to make a complete lens.

This sees glass elements ground and polished to shape. These elements then have their edges ground off, with careful attention given to ensuring the optical center of the lens is perfectly central within the element. The lenses are then coated, by vapor deposition, to give them the anti-reflective and water/oil resistant coating they might need, before having their edges blacked, to prevent internal reflections.

These lenses are then either installed into lens barrels (also made at the factory) or sent elsewhere. Although the factory can build a lens from start to finish, it also creates individual lens elements that are sent off to other manufacturers, both for Panasonic and other companies’ products.

Precision construction and checking

For the lenses that are made in Yamagata, the assembly process is pretty involved. The word that came up most often during my visit was the word ‘precision,’ and Panasonic is clearly proud of its ability both to assemble lenses with high precision and to measure and confirm that precision.

The example I was shown was the Panasonic Leica DG Vario-Elmar 100-400mm F4.0-6.3 ASPH Power OIS. It’s a fairly complex lens with 20 elements in five groups. The different groups are assembled and then introduced into the lens barrel.

Every group has to be made and positioned with high precision, but it’s impossible to make the entire lens with perfect precision. As a result, the lens is designed so that the groups that are most sensitive to tilt and centering (the ones that have the biggest effect on image quality) are adjustable.

Adjusting the 100-400mm F4.0-6.3

In the case of the 100-400mm, there are three groups that are designed to be adjusted.

The third group is adjusted for tilt and for centering within the barrel. With this done, the rest of the lens is assembled and spacing between groups one and two is adjusted. Finally, the first group is adjusted for tilt and centering.

The company says the lenses are designed to be centered to within 5?m, but the factory actually achieves less than 3?m. Tilt is supposed to be corrected to within 3/60th of a degree but the accuracy actually achieved is less than 1/60th of a degree.

Individual checks

Every lens is then adjusted for back-focus and tracking, then subjected to MTF measurements. Each unit is also checked to ensure its gyro sensors are correctly calibrated and that there’s nothing generating any unexpected mechanical noise.

Every single lens is checked, they say, and lenses are then picked at random for more extensive testing as part of the quality control process.

Aspherical expertise

But the site’s main area of expertise, and the reason other brands come to it for lenses and elements, relates to aspherical lens elements. Aspherical lenses are those whose surfaces vary in shape across their surface, such that they can’t be described by a sections of a sphere.

They’re are used to correct a phenomenon known as ‘spherical aberration,’ where rays of light passing through the edge of a lens are effectively focused at a different distance to those passing through the center of the lens. Adding aspherical lenses to a design can replace the need for multiple elements, which can help make the lens as a whole smaller, lighter, cheaper or simply better optically corrected.

The role of the die: too important to be left to chance

The key to creating an aspherical lens element, whether its glass or plastic, is the ability to precisely form the complex shape of the element. And a key part of this is creating a die: the shaped tool that presses the plastic or glass into the correct shape. The precision of the shape of these dies is essential to ensure the resulting lens element has the correct optical properties.

The factory has capacity to make around 400 dies per month, working 24 hours in two shifts. These are made from very hard metal and require high pressures for shaping them.

The molds for glass elements can be used to shape between 500 and 1500 units before they need replacing. The molds for injection-molded plastics lenses will last for around 10,000 elements before it needs replacing. The company says it takes around five weeks to go from a design to having a working mold, while the molds for glass take around 8 weeks.

Expertise + experience

This expertise has been developed over the company’s many years experience of making aspherics. For instance, its work making both glass and plastic lenses means this knowledge can be worked-in at the design stage.

Panasonic says having these expertise within the company is central to the development of new products: the factory communicates with the design team on a regular basis. During the product development process, the factory will recommend materials and manufacturing processes that the design team then takes into account when coming up with a final design. This sharing of knowledge ensures the products can take full advantage of what it’s possible to repeatably produce, using its molding technology, assembly and high-precision evaluation.

The factory once received a request for a very small compact camera, which required a very thin lens. The factory worked with designers and engineers to achieve a lens element with 0.3mm thickness: the thinnest aspherical lens element in the market at that time.

Process improvement

But, in addition to building up experience, Panasonic also takes the Kaizen approach to continuous process improvement: constantly looking, and looking to its staff, for ways to improve the way it works.

This focus on improvement has helped it refine the production quality of its aspherical lenses.

Press releases regularly talk about the number of aperture blades and their shape as the way of ensuring better bokeh, but all they do is define how circular the bokeh is. The smoothness of the lens elements also has a vital role to play: any imperfections in the lens surface can result in an onion-ring pattern appearing in the bokeh.

Panasonic found surface smoothness of the final lenses could be improved if the dies used to shape them are coated by vapor deposition (the same process used to coat lenses).

Meanwhile, the dies used for glass molding (which are subjected to much greater temperatures and forces), can be improved by hand-polishing. The factory’s ten trained polishers can take a die with 50nm roughness and take it to 20nm, again, improving the bokeh performance.

In perfect shape

A machine developed in-house, known as the UA3P (Ultra accurate 3D profilometer) checks the shape: the shape of the lens can be created to within 100nm of the intended shape.

The company says that making the small, high-resolving-power lens elements for compact cameras was very valuable for developing the facilities, technologies and skills needed to build lenses for larger cameras (Micro Four Thirds and full frame). However, some of the specific challenges are different: temperature control becomes even more critical when building lenses at larger scales.

The lens has to be cooled very evenly, to ensure both its shape and the optical properties of its glass remain consistent across the element. This requires the development of a new machine with more precise temperature control.

Looking beyond lenses, and beyond Panasonic

The factor I found most interesting was how it’s responding to a changing market. The factory was first established to make magnetic tape heads for video recorders: something that’s much less in demand than it was in 1982.

Now, as the camera market declines, Yamagata is looking for ways to adapt to market demand again, and has started making lens modules for automotive sensors and the complex mirrors needed to project a head-up display (HUD) image onto a car’s windscreen.

Even on the lens side, the demands of supporting Panasonic’s interchangeable lens business is very different to creating vast numbers of the complex lenses needed for its travel zoom compacts.

Not all Panasonic lenses are made at Yamagata and not all lenses made at Yamagata are for Panasonic

The move to making fewer, but more challenging lenses has prompted a lot of investment in new machinery. Where previously the factory had a few machines performing the same process thousands of times, it now has large numbers of machines designed to create fewer elements but with even higher precision. Interestingly, although the factory can manufacture most of the components for a complete lens, not all of the company’s lenses are built in Yamagata.

Having been rushed through the factory, there was one area we weren’t allowed to visit. This is essentially a mirror-image of the areas I was shown, but all working for another, unspecified client. Something to consider, next time you see the phrase ‘Made in Japan’ on a lens you weren’t expecting to see it on.

Articles: Digital Photography Review (dpreview.com)