Frames captured at extended intervals — clouds race across sky, flowers bloom in seconds. Interval multiplied by frame count equals real-time equivalent.
You set up the camera on a tripod, press the shutter every five seconds for two hours — and at the end, you have three minutes of footage of a plant growing. That's time lapse. Nothing more, nothing less: you collect individual frames with deliberately large time intervals and play them back at a regular frame rate (24, 25, or 30 fps). The brain perceives movement where only agonizingly slow processes are happening in reality.
The calculation is incredibly simple: if you want to show a four-hour construction site in 30 seconds, you have to trigger every three seconds. At 25 fps, you need about 250 individual frames — exactly 250 × 3 seconds = 750 seconds of real time. Modern cameras have built-in intervalometers, or you can use external triggers. In the past, this was pure manual work with a stopwatch. That led to errors, naturally.
On set, you need absolute stillness and consistency: exposure must not flicker, the wind must not drive clouds too quickly, the sun still moves — watch out for moving shadows. Many cinematographers use manual settings (no autofocus, no exposure adjustment), otherwise, each frame looks like a jump. ND filters help when it's too bright. ISO remains fixed. Shutter speed too. That's discipline. RAW footage — if the camera allows it — gives you more control over color and contrast between frames later in the edit.
The editing suite is crucial: you import the sequence, set the correct frame rate, and do a sync check. Often, you need to smooth out transitions — flicker removal tools exist for almost every NLE. Sometimes you also need ramping: ten frames per second initially, later 30 — that makes it more dramatic. Caution: time lapse can become kitschy. Sunsets, city traffic, growing plants — all seen a hundred times. The real art is to edit time lapse so that it tells a story, not just impresses. See also: Hyperlapse (added movement) and Motion Control (camera movement during interval shooting).