120 Film — The Medium Format Advantage

In the previous lesson you learned how the twin-lens reflex camera works — its two lenses, its mirror, its ground glass. But a camera is only half the system. The other half is the film, and for TLR cameras that film is 120 roll film: a format that has been in continuous production for well over a century, surviving every upheaval in photographic technology from glass plates to digital sensors. Understanding 120 film — its physical construction, its frame formats, and its optical advantages — is essential to getting the most out of your TLR.

A Format Born with the Brownie

The 120 format was introduced by Eastman Kodak in 1901, designed for their Brownie No. 2 box camera. The Brownie line was George Eastman's great democratizing project: cameras so simple and inexpensive that anyone could take photographs. The No. 2 Brownie cost two dollars — roughly seventy dollars in today's money — and used a roll of film that the photographer could load in daylight without a darkroom or changing bag.

The "120" designation is simply a Kodak catalog number. It does not refer to any measurement of the film — not its width, length, or frame count. Kodak assigned sequential numbers to their various film formats, and 120 happened to be the number that stuck. The format was an evolution of earlier roll films (Kodak's 105, 117, and others), but 120 outlasted them all. It became the standard for medium-format photography and remains so today, more than 125 years after its introduction.

The remarkable longevity of 120 film owes much to its simplicity and versatility. The same roll of film can be used in cameras producing everything from small 6×4.5 cm negatives to panoramic 6×17 cm images. No other film format offers this range of frame sizes from a single roll.

Physical Construction

A roll of 120 film consists of three elements: the film itself, a paper backing, and a spool. Understanding how these work together is important for loading and handling the film correctly.

The film strip is approximately 61 mm (2.4 inches) wide and roughly 820 mm (32 inches) long, though the exact length varies slightly by manufacturer. It is coated on one side with light-sensitive emulsion, just like 35mm film but significantly wider. The extra width is what gives medium format its advantage: more film area per frame means more resolution, finer grain, and smoother tonal gradations.

The paper backing is a strip of opaque paper slightly longer and wider than the film itself. The film is taped to the paper backing near the middle of its length, so the paper extends beyond the film at both the beginning and end of the roll. The paper serves two critical functions. First, it protects the film from light. Unlike 35mm film, which is enclosed in a metal cassette, 120 film has no cassette — the paper backing is the only thing standing between the emulsion and accidental light exposure. Second, the paper backing carries printed frame numbers and alignment marks on its outer surface, visible through the red window on simpler cameras.

The paper backing is attached to the spool — a small flanged cylinder, typically made of plastic (historically wood or metal). The spool has a keyhole-shaped slot at each end that engages with the camera's film advance mechanism. On a fresh roll, the film and paper are tightly wound around the spool with the paper on the outside. A strip of adhesive tape seals the outermost turn of paper to prevent the roll from unwinding before use.

The Spool System

One of the elegant aspects of the 120 system is how it handles spool reuse. A 120 camera requires two spools to operate: a supply spool holding the fresh film and an empty takeup spool onto which the film winds as you shoot. When you load a fresh roll, you place it in the supply chamber and thread the paper leader onto the empty takeup spool in the takeup chamber.

As you advance through the roll, the film transfers from the supply spool to the takeup spool. After you have exposed the last frame and wound all the remaining film and paper backing onto the takeup spool, you remove the full takeup spool — which is now your exposed roll, sealed by the paper backing's adhesive tab. The now-empty supply spool stays in the camera and becomes the takeup spool for your next roll of film.

This alternating spool system means you always need one spool in the camera to get started. If you are buying a used TLR and it did not come with a spool, you will need to find one before you can load your first roll. Fortunately, every roll of 120 film comes on its own spool, so after your first roll you will always have a spare. Some photographers keep several spare spools in their camera bag as insurance.

Why Paper Backing?

If you have used 35mm film, you know it comes in a light-tight metal cassette that protects the film from light at all times except during exposure. The 120 format takes a different approach: instead of a cassette, the film relies entirely on its opaque paper backing for light protection.

This design choice has several implications. On the positive side, it makes the film roll simpler, lighter, and cheaper to manufacture. It also allows the film to be loaded into the camera in moderate daylight — the paper backing shields the film during the loading process as long as you do not unwind it unnecessarily. And the paper backing provides a convenient surface for printing frame numbers, start marks, and alignment arrows.

On the negative side, the paper backing means 120 film is more vulnerable to light leaks than 35mm. Any gap in the paper, any looseness in the winding, or any damage to the camera's back or seals can allow light to reach the film's edges. This is why tight winding is important: when you advance the film in your camera, wind the advance knob smoothly and firmly to keep the roll tight on the takeup spool. And when you handle a finished roll, keep it tightly wound until you are ready to develop it.

The paper backing's frame numbers are the basis of the red window film advance system used on simpler TLRs and box cameras. The red filter over the window blocks enough light to prevent fogging the film while allowing the photographer to read the printed numbers. Different frame format sizes (6×6, 6×9, etc.) have their numbers printed in different rows on the paper backing, so the red window must be positioned to show the correct row for the camera's format.

Frame Formats on 120

One of 120 film's most remarkable features is its versatility. The same roll of film can produce different numbers of frames depending on the camera's format — that is, the size of the rectangular area the camera exposes on the film. The film strip is always 61 mm wide, and the usable image height is about 56 mm (the remaining millimeters are taken up by the edges). What changes is how much of the film's length each frame uses.

The four most common frame formats on 120 film are:

6×4.5 cm (properly 56×41.5 mm) — The smallest common medium format frame, producing 15 or 16 exposures per roll. Cameras like the Mamiya 645 and Bronica ETRSi use this format. It offers a good compromise between negative size and frames per roll, and its rectangular 4:3 aspect ratio is familiar to photographers coming from 35mm. The negative area is approximately 2.7 times larger than a 35mm frame.

6×6 cm (properly 56×56 mm) — The square format, producing 12 exposures per roll. This is the native format of virtually all TLR cameras. The square negative has an area of approximately 31.4 cm², which is about 3.6 times the area of a standard 35mm frame (24×36 mm = 8.64 cm²). We will discuss why TLRs use this format in the next section.

6×7 cm (properly 56×69 mm) — Sometimes called "ideal format" because its proportions closely match common photographic print sizes. Produces 10 exposures per roll. The Mamiya RB67 and Pentax 67 are the most famous 6×7 cameras. The negative area is approximately 38.6 cm², about 4.5 times a 35mm frame.

6×9 cm (properly 56×84 mm) — The largest common format on 120, producing only 8 exposures per roll. Used by folding cameras like the Fuji GW690 and some older press cameras. The massive negative area — about 5.5 times a 35mm frame — delivers extraordinary detail and tonal quality, but the low frame count demands careful shooting.

Why 6×6 for TLRs?

Almost every TLR ever made shoots the 6×6 square format. This is not a coincidence — the square frame is ideally suited to the TLR's design and shooting style for several reasons.

The most practical reason is that a square frame eliminates the need to rotate the camera between portrait and landscape orientations. With a rectangular format, you must turn the camera 90 degrees to switch between horizontal and vertical compositions. On a TLR, this is awkward at best: turning the camera on its side means the ground glass image is now sideways, the waist-level viewing posture no longer works, and the laterally-reversed image becomes even more disorienting. With a square frame, every composition works equally well — you simply frame within the square and crop later if you want a rectangular print.

The square format also maximizes the usable film area relative to the image circle of a typical 75-80 mm TLR lens. A circular lens projects a circular image, and a square inscribed within that circle uses more of the available area than a rectangle of the same height. This means less wasted light-gathering capability from the lens.

Compositionally, the square format has its own aesthetic character. It has no inherent "direction" — unlike a rectangle, which reads either as landscape (horizontal) or portrait (vertical), a square is balanced and neutral. Many photographers find this encourages a more centered, symmetric style of composition, while others use the square's neutrality as a starting point for more dynamic asymmetric compositions that they refine in the darkroom through cropping.

220 Film — Twice the Length, Now Discontinued

In 1965, Kodak introduced 220 film, which used the same 61 mm-wide film strip on the same spools but with two important differences. First, the paper backing was eliminated from the portion of the roll behind the film — paper was only present as a leader and trailer. This made the roll thinner, allowing twice as much film to fit on the same size spool. A roll of 220 in 6×6 format gave 24 exposures instead of 12.

Second, because there was no paper backing behind the film during exposure, the film lay slightly differently against the pressure plate, and the camera's pressure plate needed to be adjusted for the reduced thickness. Many TLRs and medium-format SLRs had a switch on the back to toggle between 120 and 220 pressure plate settings. Using 220 film without adjusting the pressure plate could result in slightly soft images due to the film not sitting precisely at the focal plane.

220 film was popular with wedding and event photographers who valued the higher frame count — 24 frames per roll meant fewer film changes during a ceremony. However, demand declined as digital photography grew, and the last manufacturer (Kodak) discontinued 220 film in the 2010s. As of this writing, no manufacturer currently produces 220 film. If you encounter a TLR with a 120/220 selector switch, leave it set to 120.

Medium Format vs. 35mm

The fundamental advantage of 120 film in any format is negative size. A 6×6 negative has 3.6 times the surface area of a 35mm frame. This size difference has cascading effects on every aspect of image quality.

Resolution and detail. With 3.6 times more film area, a 6×6 negative records proportionally more information. If you enlarge both a 35mm and a 6×6 negative to the same print size, the 6×6 negative requires less magnification. An 8×10 inch print from a 35mm negative requires roughly 8× magnification; the same print from a 6×6 negative requires only about 4.5× magnification. Less magnification means the grain structure, lens aberrations, and focusing errors are all less visible in the final print.

Grain. Film grain is a fixed physical property of the emulsion — the same film stock has the same grain structure whether it is in 35mm or 120 format. But because the medium-format negative is enlarged less to reach the same print size, the grain appears finer and smoother. A grainy ISO 400 film that looks rough in a 35mm enlargement can produce beautifully smooth prints from a 6×6 negative.

Tonal range. The larger negative captures more subtle gradations of tone, particularly in shadow areas and highlights. This is partly a function of the lower magnification (tonal transitions appear smoother when enlarged less) and partly because the larger film area can record more information at the boundaries between tonal zones.

Depth of field. To achieve the same field of view as a 50mm lens on 35mm, a 6×6 camera needs an 80mm lens. The longer focal length produces shallower depth of field at the same aperture and field of view. A portrait shot at f/3.5 on a TLR will have a noticeably creamier background blur than the equivalent shot at f/2 on a 35mm camera, despite the 35mm lens being optically "faster." This inherent depth-of-field characteristic is one of the most immediately visible differences in medium-format photographs and a major reason portrait photographers have long favored the format.

Current 120 Film Manufacturers

Despite the dominance of digital photography, 120 film remains in active production from several manufacturers. The film photography revival of the 2010s and 2020s has actually led to new emulsions being introduced and discontinued stocks being revived.

Kodak (Rochester, New York) produces Portra 160, Portra 400, and Portra 800 (professional color negative), Ektar 100 (fine-grain color negative), Gold 200 (consumer color negative), and Tri-X 400 and T-Max 100/400 (black and white). Kodak's Portra line is perhaps the most popular color negative film in medium format today, prized for its skin tones and exposure latitude.

Ilford (Mobberley, England) specializes in black-and-white films: HP5 Plus 400, FP4 Plus 125, Delta 100, Delta 400, Delta 3200, Pan F Plus 50, and XP2 Super 400 (a chromogenic black-and-white that can be processed in standard C-41 color chemistry). Ilford has been manufacturing photographic materials since 1879 and shows no sign of stopping.

Fujifilm (Tokyo, Japan) has reduced its film lineup over the years but discontinued Pro 400H in 2021 but continues to produce the Acros II 100 black-and-white film in 120 format. Fujifilm's Velvia and Provia slide films, long favorites among landscape photographers, have become harder to find in 120 but are still occasionally produced in limited runs.

Foma Bohemia (Hradec Králové, Czech Republic) makes Fomapan 100, 200, and 400 — affordable black-and-white films with a distinctive vintage character. These are popular with students and photographers who shoot high volumes.

Other manufacturers include Cinestill (repurposed Kodak motion picture film), Lomography (various color and black-and-white stocks), and Shanghai (Chinese manufacturer of budget black-and-white film). For a comprehensive guide to available film stocks, visit the metergeist film guide.

Storage and Handling

Proper storage extends the usable life of 120 film and ensures consistent results. Unexposed film should be stored in a cool, dry place — a refrigerator is ideal for long-term storage, but allow the film to reach room temperature before opening the sealed packaging to avoid condensation on the film surface. Most films have an expiration date printed on the box; professional films like Kodak Portra are designed to be shot near their production date, while consumer films have more latitude.

When handling 120 film, keep it in its sealed foil wrapper until you are ready to load it into the camera. Once loaded, shoot the roll reasonably promptly — leaving exposed but undeveloped film in the camera for weeks or months can lead to latent image degradation, resulting in color shifts and reduced contrast. After shooting, have the film developed as soon as practical, or store it in the refrigerator if development will be delayed.

The paper backing makes 120 film somewhat forgiving compared to 35mm, but it is not immune to light damage. Avoid loading and unloading in direct sunlight — open shade is fine. And always seal the paper tab on a finished roll before putting it in your pocket or bag.

Now that you understand the film, the next lesson puts everything together: loading, metering, composing, and shooting with a TLR in practice. The metergeist app can serve as your light meter when you are ready to shoot, providing accurate exposure readings tailored to your specific TLR camera.