How it works: a decade is not a filter

The idea

Hold a strip of 1960s home movie film up to a window and you are looking at the end of a long chain. Light went through a cheap zoom lens that was soft at the corners. It landed on an emulsion that saw some colors more than others. The camera's motor pulled the film past the gate eighteen times a second, never quite in the same place twice. A lab developed it, someone projected it at family gatherings, and then it sat in a tin for fifty years.

Every one of those steps left its mark, and each mark sits on top of the one before. That is why a colored overlay never looks quite right: it paints the end result without going through the chain. The Time Travel Camera goes through the chain. Every frame you shoot passes through the same ten stages, in the order the real light and the real medium met them, and the setting on the DECADE dial and the TECHNOLOGY or STYLE dial decides what each stage does.

The ten stages, in order

1. Color management. The picture from your iPhone is turned into linear light, the way a lens and an emulsion actually receive it. Blurs, glows and color mixing behave like real light only in this form.
2. Temporal sampling. What happens in time. A hand-cranked camera took 16 pictures a second, not 24, so some frames are held. In some photo styles a slow shutter adds a slight sideways blur. A double exposure leaves the last frame showing through.
3. Optics. The lens of the day: softness, darker corners, barrel distortion, colored fringes towards the edges, and the glow that bright highlights left on old film.
4. Spectral response. What the medium could see. An early black-and-white emulsion was nearly blind to red, so lips and red brick come out dark. Every color film had its own palette: warm and dense, olive greens, pastel instant prints.
5. Tone and color. Contrast, saturation and exposure, then the color cast of the medium or of its ageing, then the toning of a print or the tint of a silent reel.
6. Grain and noise. Film grain sized to the gauge (8 mm grain is coarser than 16 mm, which is coarser than 35 mm), or the electronic noise of a video sensor, plus the noise reduction and sharpening that later cameras added.
7. Recording medium. What the tape, the tube or the codec did: colors that bleed sideways on analogue video, tape noise, tracking tears, the ragged band at the bottom of a VHS frame, the blocks of digital compression, and for prints the paper and the halftone screen.
8. Physical instability. The camera in a hand, the film wobbling in the gate, the rolling shutter of a phone, focus that keeps hunting, and the light that flickers from frame to frame.
9. Ageing (optional). What time did afterwards: scratches and dust, faded dyes, yellowed whites, the silver mirror that creeps into old prints, a light leak from a camera back that didn't close properly. Most looks arrive clean from the lab. Scratches and fading belong mostly to the ones named for them, such as Aged Film Copy, Worn Analog Tape or Faded Victorian Album.
10. Output. Back to the colors of your screen, cropped to the shape you chose, with the date stamp and the decade's frame if you turned them on (a few looks print their own date). A photo's border was already painted before the ageing stage.

A photo in STILL mode follows the same path, with two differences. It is a single frame, so most of the temporal stage has nothing to do. And it gets a print border before the ageing stage, so a yellowed album print yellows on the border too, the way real paper does.

Why the order matters

Swap two steps and you get a picture that never existed. Some examples:

• Grain comes after the lens. The lens blurred the light before it reached the emulsion, so the grain on old film is sharp even when the picture is soft. Blur the grain too and you get mush, which is what a lot of filters do.
• Color response comes before toning. An early emulsion turned a red scarf dark grey first. A sepia toner then colored that grey. Tint first and the scarf would stay red under the brown.
• Tape bleed comes after the camera. On a camcorder the colors smear sideways because of how the signal was recorded, not because of the lens. So the smear runs left to right across a sharp edge, never up and down.
• Ageing comes last. Dust and scratches landed on the finished film, so they sit on top of the grain and the color, and they don't wobble with the picture.

What sets each stage

Each of the 180 video technologies and 180 photo styles is a written recipe: a medium, a gauge or format, a color response, a frame rate or a print shape, and a set of strengths from 0 to 100 for every defect. The recipes were written decade by decade from what ordinary people actually shot with. A stage whose strengths are all zero does nothing, so a clean 2020s phone look really is clean.

The DEGREE dial next to REC then turns the defects up or down without touching the identity of the look. How DEGREE works.

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