Last Updated 41 minutes ago
Filmmaking Dictionary: Number 1 / 180-Degree Shutter
Definition
A 180-degree shutter exposes each frame for half of its frame interval. At exactly 24 frames per second, the exposure time is 1/48 second. The setting is a common reference for motion blur in filmmaking.
The angle terminology comes from rotary shutters in film cameras. Digital cameras can use the same angle-based control even when they time exposure electronically rather than with a rotating mechanical shutter.
Calculating Exposure Time
Exposure time in seconds equals the shutter angle divided by 360, then divided by the frame rate. At 180 degrees, this becomes one divided by twice the frame rate.
- 24 fps: 1/48 second.
- 25 fps: 1/50 second.
- 30 fps: 1/60 second.
- 60 fps: 1/120 second.
- 120 fps: 1/240 second.
Fractional rates produce slightly different values. At 23.976 fps, a true 180-degree setting corresponds to approximately 1/47.952 second. Some displays round the number.
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Motion Blur Is a Creative Choice
A smaller angle shortens exposure time and usually produces crisper individual images of movement. A larger angle lengthens exposure time and increases motion blur, within the camera’s available range.
A 180-degree setting is not a rule that every shot must obey. Fast action, stylised movement, visual-effects requirements and practical lighting conditions can justify another angle. Judge the movement at the intended playback speed.
What Changes With Frame Rate
Keeping the angle at 180 degrees while raising frame rate makes each exposure shorter. The motion-blur relationship to the frame interval stays consistent, but the camera collects light for less time per frame.
Keeping a fixed shutter speed instead produces a different angle relationship when the frame rate changes. This is a common source of unexpected blur or exposure changes when moving between normal-speed and slow-motion recording.
Flicker and Lighting Tests
A conventional shutter angle does not guarantee freedom from flicker or banding. Lighting modulation, mains frequency, dimmer behaviour and camera timing can interact. Test the actual fixtures at the intended frame rate and exposure setting.
Example on Set
A crew changes from 24 fps to 120 fps while retaining 180 degrees. Exposure time changes from 1/48 to 1/240 second. The lighting and exposure plan must account for that shorter interval, and the high-speed test should include any practical lights visible in frame.
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Frequently Asked Questions
Is this the same as the 180-degree rule?
No. The shutter angle controls exposure timing; the continuity rule concerns camera positions around an action axis.
Does 180 degrees always mean 1/48 second?
No. That value applies at exactly 24 fps. The exposure time changes with frame rate.
Related Terms
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