Hyperlapse and Day-to-Night Planning

Updated

The planning math for the two harder time-lapses: how far to move the camera between frames and how much to crop for stabilizing, and how to time and ramp the exposure from daylight through twilight into night.

9 min readAdvanced
  • Hyperlapse
  • Holy grail
  • Twilight
  • Exposure ramp
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Hyperlapse: the camera moves

A hyperlapse is a time-lapse where the camera travels between frames: along a street, across a bridge, round a building. The frame count and interval come from the same formulas as any time-lapse (see the time-lapse calculator guide). Two more numbers decide whether it works: how far to move between frames, and how much picture to keep spare for stabilizing.

Distance per frame

Step length
Frames = Clip length (s) × Frame rate Step = Path length ÷ Frames

Example: A 120 m walk across a bridge, 8-second clip at 24 fps

Calculation:
Frames = 8 × 24 = 192; Step = 120 ÷ 192 = 0.625 m
Result:
Move 62.5 cm between frames: mark the path every 62.5 cm, or count paving slabs

The interval in a hyperlapse is set by you, not by the event: the time it takes to move one step, re-aim at the same point on the subject and fire. If that takes 5 seconds, 192 frames take 192 × 5 = 960 s, 16 minutes on location. Shorter steps give smoother motion and a slower-looking move; longer steps cover more ground per second of screen time.

Crop margin for stabilizing

Stabilizing a hyperlapse shifts, rotates and scales each frame, which needs picture outside the final frame. Shoot wider than you deliver and the difference is your margin.

Width kept and margin
Kept = Output width ÷ Capture width Margin each side = (1 − Kept) ÷ 2

Example: UHD output (3,840 px) from stills 6,000 px wide (an assumed sensor width)

Calculation:
Kept = 3,840 ÷ 6,000 = 64%; Margin = (1 − 0.64) ÷ 2 = 18%
Result:
18% of the width spare on each side for the stabilizer to use

Frame the shot looser than you want it to end up, so that the subject still sits where you want it after the crop.

Day-to-night: the light changes

A day-to-night time-lapse, often called a holy grail, runs from daylight through sunset and twilight into darkness. The camera usually stays put; the problem is exposure. The light falls by many stops over the shot, and the exposure has to follow it smoothly enough that the change is invisible frame to frame.

When the light goes

The US Naval Observatory defines the stages by the Sun's angle below the horizon. Sunset is when its upper edge touches the horizon; civil twilight ends when its center is 6° below, nautical twilight at 12° and astronomical twilight at 18°. The minutes between those angles change with latitude and season, so look up the times for your location and date (the USNO data service gives them) rather than using a rule of thumb.

  • Start before sunset, so the shot opens in daylight.
  • Expect the fastest change around and after sunset, through civil twilight.
  • End after the sky has gone dark enough for your shot; for stars, that is after nautical or astronomical twilight.

Ramping the exposure

The interval in a day-to-night shot is set by the night end, because the longest exposure of the sequence has to fit inside it. Work the interval out from the event and the clip as usual (the free time-lapse calculator does it in your browser), then check the night exposure fits.

Case study

Sunset to night over a city

Scenario

Shoot from 30 minutes before sunset to an hour after: 90 minutes, for a 15-second clip at 24 fps.

Challenge

Find the interval, check the longest night exposure fits, and plan how often to change the exposure.

Solution

  1. Frames and interval from the time-lapse formulas.
  2. The night exposure has to finish, and the frame be written, inside the interval.
  3. Spread the total exposure change across the frames in the camera's 1/3-stop steps. Here we assume a test the evening before showed a 10-stop drop; measure your own scene.

The numbers

  • Frames: 15 × 24 = 360; Interval: 5,400 ÷ 360 = 15 s; Speed-up: 5,400 ÷ 15 = 360×
  • Longest exposure: under 15 s, less the camera's write time
  • Steps: 10 stops × 3 = 30 changes of 1/3 stop; 360 ÷ 30 = one change every 12 frames

Result

A 15-second interval, night exposures kept under about 13 seconds, and a 1/3-stop change roughly every 12 frames (every 3 minutes), more often around sunset.

Key takeaways

  • Keep the aperture fixed: changing it shifts depth of field and can flicker. Ramp shutter first, then ISO.
  • Set white balance manually and change it in the grade, not in camera.

The light does not fall evenly, so a fixed schedule is only a starting point. Watch the histogram and change exposure when it has drifted by about a third of a stop. Intervalometers and apps that ramp the shutter automatically (often called bulb ramping) make the steps smaller and more frequent, which is easier to smooth later.

Deflicker and the edit

Each exposure change leaves a small step in brightness, and the shot flickers if you play it straight. Shoot raw so you have room to correct, then use a deflicker tool or keyframed exposure in the grade to smooth the steps into a continuous ramp. Leave a few seconds of extra frames at each end for handles.

Storage is the same sum as any time-lapse: frames × file size. 360 raw frames at an assumed 50 MB each is 18 GB. The recording media guide covers card capacity and offload time.

Next step: set the event length, clip length and frame rate in CineMath's Time Lapse calculator, or the free time-lapse calculator in your browser, to get the interval, then check the night exposure fits inside it.

Calculators for this guide