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6
Lens testing room

Since optics are the core of any lens, we’ll start with glass. Before diving into the manufacturing process, let’s talk about how Sigma establishes performance metrics for every lens it manufactures.

Each time a new lens is designed, a high-quality master copy is created which is used for benchmark testing; it establishes a baseline performance spec for each new interaction constructed. This baseline becomes the reference point for all Modulation Transfer Function (MTF) machines used throughout the lens manufacturing process, ensuring that each lens meets the design specification for resolution. Sigma designs and builds its own MTF machines in-house.

Testing of the master lens takes place on a Trioptic measurement machine, one of only a few of its type in Japan. It can measure the range between the minimum focusing distance and infinity for all of Sigma’s lenses and uses collimators up to 1000mm.


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Glass: lens blanks

Most lens elements start as lens blanks, glass disks with a slight curve. Before any grinding occurs, lens blanks have an opaque, white appearance. Sigma uses lens blanks from Hoya to manufacture its lenses.


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Glass grinding

The first step in the lens manufacturing process is to roughly grind out the curve of the lens. Each lens blank is attached to a plunger that guides it into a machine where the glass is ground to the correct curve for the lens. Since this part of the process is intended only to create the right shape for the lens, it still appears somewhat opaque when finished.

A second, more refined precision grinding step is then performed, which gives the lens its clear, smooth finish.

There are about 330 machines used in the glass manufacturing process at Sigma’s Aizu factory, and every few minutes a technician is checking one with a gauge to ensure that its curve is correct.


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Lens polishing

After the lenses are ground, the third and final step is polishing. Lenses are set into a machine on polyurethane pads mounted in a mold that matches the final shape or curve of the lens. These grind the lens using a special polishing paste, typically cerium or zirconium oxide. The process usually takes two to ten minutes, depending on the size and type of the lens.


Go inside Sigma's factory to see how lenses are made


10
Lens coatings

Once lenses are polished or molded, it’s time to apply Sigma’s Super Multi-Layer coatings, which suppress flare and ghosting. Before applying coatings, each lens is visually inspected for dust. The lens is then loaded onto a ‘planet,’ a dome-shaped device with inserts for specific lens elements.

The planets are then loaded into machines in which special chemicals have been evaporated into a chamber. The planet rotates inside the device, evenly spreading the vaporized chemicals onto the lens elements, before holding them to be cured by UV light.


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Lens caulking, joining and bonding

Once the individual optical elements are manufactured, those that get grouped in a lens go through a process called caulking and joining. Each element is placed into a plastic frame, and high heat and pressure are used to fix them into place, creating a single unit made of multiple lens elements.

A separate process called lens bonding (photo above) is used when two to three elements must be bonded directly with no space in between. The two lenses are joined with a special adhesive, and a machine ensures that both lenses are optically centered. The bonded lenses are then exposed to UV light to cure the adhesive.


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Metal processing

Now that we’ve covered glass, let’s move on to the rest of the manufacturing process, starting with metals. A lens has many metal parts, so metal processing covers a large part of the factory floor, producing components out of materials like steel, aluminum and brass.

The automated blue machines visible in the photo above carry out the process of cutting out, shaping and drilling holes in metal for a perfect fit. The process is quick, often taking only a few minutes per part. The factory runs about 160 of the machines you see in the photo.


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Metal processing

Although numerous parts are produced in this factory area, lens barrels and bayonet mounts are the most recognizable. This photo shows freshly milled inner rotation barrels for lenses before any surface treatment has been applied.



21
Surface mounting

Surface mounting refers to mounting electronics onto circuit boards for lenses. As with many things, Sigma manufactures circuit boards in-house. Baseboards are fed into one end of a machine where soldering paste is applied and heated to spread out the paste evenly. Components are then fed into the machine from rolls that look like tape and stamped onto the board.


30
Projection room

The projection room, located next to the customer support and service area, is used to test products before and after repair. On the opposite side of the room, there’s a reverse projector for testing Sigma’s cinema lenses.

Sigma’s standard practice is to test lenses on both the resolution chart and MTF machine to ensure that they meet Sigma’s product specs before returning them to customers.

Additionally, technicians will even go outside to take real-world before and after photos to check a lens depending on the nature of the repair, for example to check for flare.



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Sigma museum

Of course, no visit to Sigma would be complete without a trip to the Sigma museum, where it’s possible to see cameras and lenses past and present. There’s a lot to see, including modern lenses, classic lenses, SA-mount lenses and even cameras, like Sigma’s SD10 DSLR or compact Merrill models.

Finding some of the lenses you used early in your photography career is a fun, nostalgic trip down memory lane.



Sigma's factory in Aizu, Japan


https://www.dpreview.com/articles/5410838737/go-inside-sigma-s-factory-to-see-how-lenses-are-made




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