Behind the scenes · Dunna Did It × Freewell

A camera filter starts as two very ordinary-looking things: a piece of aluminum and a sheet of glass. Turning them into something you can trust in front of your lens takes machining, cleaning, coating, careful assembly and a long series of checks.

We welcomed Dunna Did It to our factory to see that journey for himself. He helped develop the filters that carry his name. This visit let him meet the people and see the work behind the product he had been testing remotely.

The result is a rare look at a process usually kept off camera. There are machines doing precise, repeatable jobs, and people checking threads, placing magnets, aligning glass and preparing each filter to leave the factory. Follow the visit below, then watch Dunna’s complete film at the end.

It starts with a ring that has to fit

The metal side begins with aluminum. CNC machines cut the material into the components needed for the system, including base rings, filter frames and cap parts. It is the first step in making separate pieces work together as one filter.

Think about the base ring for a moment. It is the connection between your lens and the rest of the system. You want it to screw on smoothly, sit correctly and give you a dependable starting point for each filter change. A good optical element cannot solve a poorly fitting mount.

Dunna explains that the black or colored finish is applied outside the factory. The components return for the next stages. That distinction is part of the tour: the finish is the step he identifies as happening elsewhere.

Every base ring gets a thread check

A thread size on a lens is a nominal measurement. Two lenses marked with the same diameter still have manufacturing tolerances. The base ring has to work within an acceptable range, rather than fitting only one unusually tight or loose example.

At the checking station, each base ring is tested against minimum and maximum limits. It is a small, repetitive job with a direct effect on the person using the finished product. The moment you attach a ring to your lens, you experience the result of that check.

The identification is engraved into the metal

Before the glass goes in, the metal components receive their laser engraving. Filter type, strength, size and branding need to remain easy to identify when several filters are in your bag.

For Dunna, this stage also makes the collaboration tangible. Seeing his name engraved on a component is different from reviewing a prototype or sending feedback from his desk. The finished markings are being made in front of him.

A sheet of glass becomes an optical surface

While the metal components take shape, the glass follows its own route. Optical glass arrives in large sheets protected in crates. It is cut down into the circular pieces that will eventually sit in the filter frames.

The discs then go through a wash using highly purified water. The tour also shows the factory’s water purification equipment. Cleaning at this stage prepares the glass for inspection and the work that follows, rather than simply making it look tidy before packing.

Each piece is checked for imperfections before continuing. This is an easy stage to overlook when you only see a sealed filter box. Inside the factory, inspection is part of the journey long before the final assembly.

Why the coating room has its own entry routine

Entering the coating area requires protective clothing and a cleaning airlock. Dust control matters because the next stages work directly on the optical surfaces. Dunna gets to experience that change of environment as he moves deeper into the production process.

Inside, the glass discs are loaded into domed metal racks. The shape lets multiple pieces sit in the coating equipment together. It is one of the most striking images from the visit: many small optical surfaces arranged across one large curved holder.

The process described in the film takes approximately six to eight hours in the machine. Dunna breaks it into separate rounds for the two sides of the glass and a protective top coat intended to help resist water, oil and scratches.

That number describes the coating stage shown in this tour. A finished filter also needs all the machining, cleaning, inspection, assembly and testing around it. The short time it takes to attach a filter on location gives very little sense of the time that went into its surfaces.

An ND filter has to reduce light predictably

A filter can look evenly dark to your eye and still need an optical measurement. After coating, the glass is tested to see how much light passes through it across the visible spectrum.

For an ND filter, the aim is controlled light reduction with as little unwanted color influence as possible. An ideal ND8 passes one-eighth of the incoming light, which is three stops of reduction. The transmission curve helps show whether that reduction stays consistent across different visible wavelengths.

If the transmission varies with wavelength, the image can pick up a color cast. That is why the test goes beyond asking whether the glass looks dark enough. It checks the behavior you are relying on when you use ND to hold your chosen exposure settings.

The camera test still matters

One of the most useful parts of the visit connects factory measurement with Dunna’s own prototype testing. He had used a chart on his wall to examine the results. The team recreated a similar setup at the factory to investigate what he was seeing.

Instrument readings and a creator’s camera test answer related questions. The measurement gives a controlled view of the filter’s behavior. The camera setup helps the team reproduce a specific experience and work through the feedback. Seeing both makes the development process easier to understand.

The filters behind the visit

Choose how you create

Explore the filters made through the process you have just seen. Our Dunna Did It × Freewell filter-system guide takes you through the ultra-slim design, magnetic locking connection and kit options.

For motion

Videography Kit

ND4 · ND8 · ND16 · ND32
Glow Mist 1/4

CHOOSE VIDEO KIT →

For stills

Photography Kit

UV · CPL · ND64 · ND1000
Glow Mist 1/8

CHOOSE PHOTO KIT →

Where the metal and glass finally meet

After the glass has been prepared and checked, the two production routes come together. The tour includes silk screening around the edge of the glass, followed by the assembly work that turns the separate components into a usable filter.

At the magnet stage, a machine dispenses adhesive into the required positions. A person places the small magnets by hand, and the parts go through a drying stage so the adhesive can set before assembly continues.

This is the part of the story you feel each time you change filters. The quick magnetic connection begins with a collection of small parts that have to be placed and secured correctly. For this system, attachment is followed by a clockwise twist to engage the lock.

The small detail behind a smooth-turning CPL

A circular polarizer needs an adjustment the solid ND filters do not: its optical section rotates while the base stays connected. That movement lets you control the polarization effect as you look at reflections in the scene.

Dunna had assumed that the smooth feel came from a bearing. On the tour, he learns about the carefully controlled amount of fluid used between the sections. The resistance has to be tuned. Too much makes the adjustment stiff; too little makes it easier for the position to move unintentionally.

He explains that this feel was refined during the prototype process. It is an unusually clear example of how creator feedback becomes a manufacturing decision. A request about how something should feel in the hand turns into a controlled assembly step.

The CPL glass is also aligned by hand during assembly so the polarization orientation starts consistently across the filters. You still rotate the CPL to find the effect you want in a particular scene.

For reflection control, the Dunna Did It CPL uses the same magnetic locking approach. Match it with the correct Dunna base ring; the standalone CPL is sold without a base ring or lens cap.

Then comes the room built to wear things out

The testing room changes the mood of the tour. After watching components being cleaned and assembled carefully, Dunna sees equipment intended to put materials and products under stress.

He describes scratch and abrasion tests, heat and cold tests, and tests that simulate rough handling of packaged goods during shipping. The purpose is to examine how a product or package responds to specific conditions before relying on it in everyday use.

These are controlled evaluations. The film does not supply a universal drop height, a guarantee against every scratch, or a promise that glass cannot break. What it shows is the equipment and work behind durability checks, alongside the optical and mechanical checks elsewhere in the factory.

Tempered ND glass, with an important distinction

Dunna points out that the ND glass in his filter system is tempered. He also explains that the CPL and Mist filters use a different bonded-glass construction and are not tempered. It is useful information when you are comparing filter types within the same family.

Different optical functions can require different construction. Treat the glass with care, keep it protected between uses and avoid assuming that a feature described for the ND filters applies to every other filter in the system.

Packing is part of the process

Once the filters have been assembled and tested, they are boxed, wrapped and given serial identification. The tour explains that this identification supports tracing a filter back to its production history, including the day it was made and the person involved.

Even the wrapping has a reason behind it. Dunna recounts that the team had tried leaving out the shrink wrap, then brought it back after seeing the white boxes change color while stored. It is a modest detail, but a useful example of a production choice shaped by experience.

What the visit means when you pick up your camera

The factory tour makes the connection between a manufacturing step and a familiar action. Screwing on the base ring connects to the thread check. Reducing light connects to the transmission measurement. Turning a CPL connects to the adjustment made during assembly.

It also puts people back into the picture. Machines handle cutting, dispensing and measurement, while workers inspect components, place magnets and assemble the filters. Dunna arrives knowing the product’s behavior from his own tests and leaves having seen how those details are made.

Near the end, the film includes a deliberately oversized stack of connected filters to demonstrate the locking connection. For shooting, follow the product guidance: stack no more than three compatible filters for best results. A connection demonstration is not a recommendation to build a tall stack in front of your lens.

If you want to explore the system in more detail, our Dunna Did It filter system guide explains the mounting approach and filter options. The 82mm Videography Kit combines ND4, ND8, ND16, ND32 and Glow Mist 1/4 with an 82mm base ring. Choose your size from the lens thread marking, using our filter-size guide if you need help.

Next time you attach a filter, you will know a little more about the journey behind that simple movement: two materials, many production stages, and a team working on details that end up in your hands.

Frequently asked questions

Watch Dunna’s complete factory visit

See the production floor, hear the explanations and follow the process in Dunna’s original film, How My Camera Filters Get Made (Freewell Factory Tour).

Watch the full factory tour on YouTube