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Filmmaking Dictionary: Number 5 / 50 fps
Definition
50 fps means fifty complete frames are captured or displayed each second. In progressive video, this is often written as 50p. It is used for smooth real-time movement and for footage that will be slowed down in a lower-frame-rate timeline.
Capture rate and playback rate must be distinguished. A clip recorded and played at 50 fps runs at normal speed. The same fifty captured frames played at 25 fps take two seconds, producing half-speed motion without inventing extra frames.
50p Is Different from 50i
A 50p signal contains fifty complete progressive pictures per second. A conventional 50i signal contains fifty interlaced fields per second, forming twenty-five frame periods. The labels therefore describe different picture structures and motion sampling, even though both include the number fifty.
Changing an export label does not turn interlaced footage into genuine progressive capture. Deinterlacing and frame-rate conversion need appropriate processing, particularly when subjects move quickly or fine horizontal detail is present.
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Shutter and Exposure
- At 50 fps, a 180-degree shutter corresponds to approximately 1/100 second.
- Compared with 25 fps at the same shutter angle, each frame receives half as much exposure time.
- Maintaining brightness may require a wider aperture, more light or a suitable sensitivity adjustment.
- Lights and displays should be tested for flicker at the actual camera settings.
Production Example
A filmmaker shooting a 25 fps project records a brief action detail at 50 fps. Conforming that shot to 25 fps gives clean half-speed playback. Recording every scene this way would complicate normal-speed dialogue and change the treatment of sound, so the slow-motion requirement should be planned shot by shot.
Some cameras separate recording frame rate from project or playback rate in an off-speed mode. Such clips may already arrive with slow playback and may not include usable synchronized audio. Check the file behaviour before relying on a sound recording from the camera.
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Frequently Asked Questions
Is 50 fps automatically flicker-free under 50 Hz power?
No. Light output depends on the fixture and its electronics, not just mains frequency. Shutter timing also matters.
Can 50 fps become slow motion in a 24 fps project?
Yes. Playing all captured frames at 24 fps gives 48% speed. Decide how sound and any real-time shots will be handled.
Related Terms
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