A cut-in half Canon EF 400mm F2. 8L IS II lens from 2010, shown surrounded by all the components from which it's made, in the foyer of Canon's Utsunomiya factory. Photo: Richard Butler "RF lenses are better," said Go Tokura, head of Canon's Imaging Group: "they are adjusted digitally, giving more consistent results.
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These words tumbled around my head as the Tohoku Shinkansen raced us from Tokyo towards the Canon lens factory in Utsunomiya, about 110km (70mi) north of the capital.
I'd been fortunate enough to be seated at Tokura's table at dinner the night before. Despite the language barrier, we were able to talk a little about lenses over scribbled sample variance graphs. It had been clear he wasn't referring to digital distortion corrections, but I couldn't be totally sure what he meant. The Utsunomiya factory is home to both a production facility and much of Canon's lens development facilities, so I was hoping I'd find my answer there, in amongst the messages the company wanted to communicate.
The E5 series train of the Tohoku Shinkansen that took us from Tokyo to Utsunomiya.
Photo: Richard Butler
Canon describes Utsunomiya as its flagship lens facility, where it builds its broadcast lenses, as well as many of the high-end, L-series photographic lenses and optics for semiconductor manufacture. Canon also has factories in Taiwan and Malaysia, where many of its less expensive lenses are produced.
Canon says it builds its different products to different tolerances, with L-series super telephoto lenses requiring 15x the precision of the lenses in its point-and-shoot compacts, whereas broadcast lenses are made to 70x the precision and its industrial applications (including equipment for semiconductor lithography) demand tolerances 1500x finer.
That was a recurring aspect of everything we saw in the factory: different processes and varying technologies depending on the scale of production and the cost of the end products. And while, understandably, Canon wanted to demonstrate the highest precision work it does, it was the degree to which this know-how filters down and gets mimicked or adapted to large- and mass-production scales that interested me.
Varying aspherics
A Canon master craftsman demonstrates a glass element following machine polishing.
Photo: Richard Butler
For instance, the company says it uses four different types of aspherical elements in its different products. Sometimes the size of the element dictates which technology is used but the production scale: how many it has to make, also plays a critical role.
At one end of the scale are conventional ground glass aspherics, which need to be carefully polished to yield the perfect shape. To achieve the perfect shape, meticulous adjustments must be repeated over and over. It’s a delicate process that demands a significant amount of time and precision.
However, the process is too time-consuming and expensive to apply when you're making large numbers of lenses, so Canon has developed a series of other aspheric technologies. This includes glass molded aspherics, where molten glass is pressed between metal molds. As we this was being explained, it was impossible to ignore the heat and light radiating from the array of large metal and glass equipment stretching to fill the rest of the room. During the time it took to show us glass elements being polished, those molding machines continued their work, pressing and forming element after element.
The $2600 Canon RF50 F1. 2L on the left includes a polished glass aspheric element as well as other, unspecified aspherics. The $470 Canon RF1. 2 STM on the right uses a less expensive plastic molded aspheric that is more easily produced in large volumes.
Photo: Richard Butler
These glass-molded elements still need a degree or polishing, but can be created in much greater numbers. Sitting between these two technologies are what Canon calls "replica aspherics" where a molded resin layer is bonded onto a (compartively easy to make) spherical glass element. We were told this technology has been refined since it was first used on EF lenses, and is now able to deliver several times more deviation from spherical shapes and with several times more accuracy for elements used in the latest RF-mount designs.
Plastic molded aspherics, used in compact camera lenses and the likes of the RF28mm F2. 8 STM and the new RF45mm F1. 2 STM are made in other facilities, allowing the use of complex elements in lower cost products.
The company says its lens polishers continue to get better, meaning the lens designers can design even more ambitious lenses and know they can be manufactured. But they also say they're constantly trying to recreate some of the skills in automated processes. And it's this ability to produce aspherics on larger scales, and improvements in the quality of those elements that is driving up the performance of a lot of the lenses we encounter.
Material advances
Much of the factory visit was built around showing-off details like this. For instance, Canon demonstrated the Blue Refractive optics glass that bends short wavelengths of light to a greater degree than longer wavelengths, allowing its use to correct axial chromatic aberrations (the colored fringes on out-of-focus highlights). The glass was first used in Canon's EF35mm F1. 4 L II USM but has been the continuously developed since then, with an improved version being deployed in the recently released RF20mm F1. 4 L VCM. As with the improvements in replica aspheric production, we were told how much more effective the new material was, but asked not to report the specific number.
Assembly and alignment
A Canon technician inspects a lens element before it's installed into an assembly of an RF100-300mm F2. 8L IS USM.
Photo: Richard Butler
Towards the end of our tour, we followed the assembly process of the RF100-300mm F2. 8L IS USM (there are videos on YouTube showing this part of the tour). It's a multi-stage process of assembling, aligning and adjusting lenses, with a series of technicians each focused on one step of the process, overseen by a highly experienced staff member known as a 'meister. '
Much of the process is done by hand, with checks of each process along the way. Then, at the end, one technician's job is to ensure the different groups are correctly aligned. The 100-300mm has 23 elements arranged in 18 groups, and each attempt to correct the alignment of one group or assembly can then highlight an issue with another, resulting in an iterative process, bringing the lens closer and closer to the designed performance level.
This way of working, with around six technicians and a meister, allows Canon to produce nine 100-300mm lenses per day. It has the advantage that the technicians can easily turn their attention to the construction of other lenses, when a batch of 100-300s is complete. The same workstations can also produce Canon's 400, 600, 800 and 1200mm RF lenses, along with the EF400mm F2. 8L IS III USM, which we were told is the last EF ultra-tele still in production.
A workstation in which multiple assemblies are brought together as an RF100-300 F2. 8L IS USM comes together.
Photo: Richard Butler
Further along on the tour we were shown a large rectangular box, the size my last flat in London, full of robotic arms and conveyor belts, that conducts many of the same steps: inserting and UV-bonding circuit ribbons into lens assemblies, adding rollers and springs on which internal cams can move, attaching and assembling the USM motors around the focus groups. Lens elements already positioned in plastic lens assemblies were fed in at one end of the machine and a series of robot arms carefully conduct each step of the process as the lens passes through cubicles within the box, each containing a machine playing the role of a single technician.
The machine we were shown was making EF 24-105mm F4L IS II USM lenses but can be reconfigured to make EF 16-35mm F2. 8L III USM: the two lenses having been designed with similar layouts and a high degree of shared componentry to allow one series of robots to build either lens. Unlike the hand-made approach, the whole setup would need to be significantly redesigned and rebuilt to be able to assemble any other lens, at significant investment cost.
A technician iteratively adjusts the different elements of an RF100-300 F2. 8L IS USM, carefully monitoring the ways in which each adjustment improves and degrades the performance.
Photo: Richard Butler
Alignment checking wasn't done within this machine, instead being conducted later, manually. But we were then whisked past a machine assembling RF lenses and told that this machine performs the iterative process of assessing and fine-tuning lens alignment, automatically. Here was the digital adjustment that Go Tokura had been referring to, when he said that RF-mount lenses are being built to a higher standard and with greater consistency: automated fine-tuning of alignment, in a way that was previously only possible for ultra high-end lenses produced by hand.
Trickle-down technology
It's not just Canon making constant improvements, of course. But it's interesting to get an insight into the small improvements that, cumulatively, have seen lenses improve dramatically over the last ten or so years. Aspherics becoming easier to make and hence more readily used in new lens designs, constant improvement of optical materials and advances in production processes all keep pushing lens performance upwards.
The visit to the Utsunomiya factory let me find out what the head of Canon's camera business, Go Tokura (left) had told me, the evening before.
Photo: Canon
The Utsunomiya factory is primarily focused on very high-end lenses, but what stood out to me is the way Canon has tried to adapt its highest-precision but labor-intensive manufacturing methods so that some of those benefits can appear in lenses we can actually afford. I could see why Tokura wanted to share his enthusiasm for that.
This article was prepared as part of visit to Japan paid for by Canon. You can read more about it, including insights from senior managers, in this original article.
. dpreview.com2025-11-12 18:00
