Aspect ratio, explained: why the shape of the frame keeps changing

The black bars are not a defect and the image is not being stretched. Every film is shot in a specific frame shape, called the aspect ratio, and the bars are simply the space left over when that shape meets the shape of your screen. Once you know the handful of numbers, a lot about a film becomes legible.

The numbers, and what they mean

An aspect ratio is width divided by height. The common ones: 1.33:1 (also written 4:3), the near-square shape of silent and classic studio cinema and of standard-definition television; 1.85:1, the flat widescreen ratio that became the American default; 2.39:1 (often called 2.35 or 2.40), the anamorphic scope shape, wider still, used for epics and for films that want the frame to feel panoramic; 1.78:1 (16:9), the shape of HDTV and most streaming; and 1.43:1, the near-square IMAX ratio that a small number of productions shoot into. Ratios are often written as decimals or as X:Y pairs and they are interchangeable — 1.78:1 and 16:9 are the same shape.

Why cinema went wide

For decades there was one shape, because there was one standard and no competition for it. Television changed that: when audiences stayed home to watch small square pictures, studios responded by making the cinema frame something television could not reproduce. The 1950s produced a burst of competing widescreen processes, anamorphic lenses that squeezed a wide image onto standard film, and projection systems built for it. The shapes that survived — 1.85 and 2.39 — are the survivors of a format war fought against the living room, which is the reason the two ratios are still the defaults seventy years later.

Why a film changes shape halfway through

Because different scenes were shot with different cameras. A production that uses IMAX cameras for certain sequences captures a taller image for those scenes — 1.43 or 1.90 depending on the system — and the rest of the film at its standard ratio. When the film switches, the picture genuinely expands: the bars disappear or change size because there is more image, not because anything is being zoomed. Directors use it deliberately, opening up the frame for spectacle and returning to the narrower shape for dialogue. It is a creative choice with a technical cause, and it is the single most common reason people think their television has broken.

What your screen is doing to it

A 2.39:1 film on a 16:9 television has to be letterboxed — bars top and bottom. A 4:3 film on the same television gets bars at the sides, called pillarboxing. The alternative to bars is the thing that used to happen on television: pan and scan, where the image is cropped and repositioned to fill the screen, throwing away sometimes half the frame and moving the crop around to follow the action. It is the reason older films look wrong on old broadcasts. Most modern players and televisions default correctly now, but zoom and fill settings still exist, and if a film looks wrong the first thing to check is that the player is set to the original ratio rather than to fill.

Why the frame shape is a creative instrument

Ratio is a compositional tool, not a technical constraint. A wide frame separates characters across the image and suits landscapes, crowds and isolation; a near-square frame stacks faces and suits interiors and dialogue; changing ratio mid-film signals a change in register. Recent cinema has also broken the assumption that films should get wider and less square — several acclaimed films have shot at 4:3 or 1.33:1 precisely because the narrower frame does something the widescreen one cannot, and the vertical frame of phone-made work is now its own grammar. The frame is the first decision a film makes about how you will look at it, which is why it is worth noticing.