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About this tool
Work out the capture frame rate, speed percentage, shutter speed and light loss for any slow-motion target.
This planner converts between capture frame rate and slow-motion factor, because slow motion is nothing more than the ratio of the two: factor = capture fps ÷ timeline fps, and the speed percentage you type into an editor is 100 ÷ that factor. It then works out the two things that actually decide whether the shot is achievable — the shutter speed implied by your shutter angle (angle ÷ 360 ÷ fps, so 1/480 s at 240 fps with a 180° shutter), the stops of light that costs against the 1/48 s of 24 fps, and whether the capture rate will band under mains lighting, which pulses at 100 Hz on a 50 Hz supply and 120 Hz on 60 Hz.
Open Slow Motion Frame Rate Planner on AltFTool — it loads instantly in your browser.
Enter the values you already know.
Fine-tune the options to match your scenario.
Read the result and use it in your planning or reporting.
Enter a capture rate and get the factor, or name the factor and get the rate to dial in.
Shows the shutter speed and the stops lost before you discover them on location.
Tests both the frame interval and the shutter against the 100 Hz or 120 Hz light pulse.
Multiply your timeline frame rate by 5. For a 24 fps timeline that is 120 fps, which you then play at 20% speed in your editor; for a 25 fps timeline it is 125 fps, so most people shoot 120 or 150 and accept the slightly different factor.
Each doubling of frame rate at the same shutter angle costs one stop. Going from 24 fps to 240 fps with a 180° shutter takes the exposure from 1/48 s to 1/480 s — 3.3 stops, or about ten times less light reaching the sensor, which is why high-speed work is usually lit hard or shot in daylight.
Mains-powered lighting pulses at twice the supply frequency — 100 Hz on a 50 Hz supply, 120 Hz on 60 Hz. Exposure only stays even when the frame interval or the open shutter spans a whole number of those pulses. Above the pulse frequency that becomes impossible, so any capture rate over 100 or 120 fps needs flicker-free DC or high-frequency ballast fixtures.
Keep 180° unless you have a reason not to. It preserves the same proportion of motion blur per frame as normal-speed footage, so the slowed shot still looks natural. Opening towards 360° buys back a stop of light at the cost of softer motion; closing towards 45° gives a crisp, strobing look and costs light you probably cannot spare.
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