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Filmmaking Dictionary: Number 9 / 90° Shutter
Definition
A 90-degree shutter exposes each frame for one quarter of its frame interval. Shutter angle expresses exposure duration as a portion of a full 360-degree cycle. At 24 fps, a 90-degree shutter gives an exposure time of approximately 1/96 second.
The general relationship is exposure time = shutter angle ÷ (360 × frame rate). The same angle therefore produces different exposure times at different capture rates. Always specify the frame rate when translating angle into shutter speed.
Effect on Motion Blur
Compared with a 180-degree shutter at the same frame rate, a 90-degree shutter exposes each frame for half as long. Moving subjects generally show less blur within each frame, which can create a sharper, more abrupt impression of action.
That does not mean the movement contains more temporal samples. Frame rate has not changed. A fast pan can still look juddery, and the reduced blur may make individual frame transitions more noticeable.
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Exposure-Time Examples
- At 24 fps: approximately 1/96 second.
- At 25 fps: approximately 1/100 second.
- At 30 fps: approximately 1/120 second.
- At 60 fps: approximately 1/240 second.
Moving from 180 degrees to 90 degrees costs one stop of exposure at a fixed frame rate. Maintaining image brightness requires an appropriate change to lighting, aperture or camera settings, each with its own consequences.
Practical Production Example
A director wants a fight sequence to feel more abrupt and detailed during movement. The cinematographer tests a 90-degree shutter with the actual choreography and camera movement. The test reveals whether the reduced blur supports the scene or makes the action unpleasantly fragmented.
The lighting test matters too. Shorter exposure times can reveal flicker from practicals, LED drivers or screens. A shutter chosen for motion character may need adjustment when the location’s light sources behave poorly.
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Frequently Asked Questions
Does a 90-degree shutter create slow motion?
No. Slow motion depends on the relationship between capture and playback rates. Shutter angle mainly changes exposure duration and motion blur.
Does 90 degrees describe the camera’s position?
No. It is unrelated to a ninety-degree camera angle, lens field of view or the 180-degree continuity rule.
Is it always the best setting for action?
No. Test it against the movement, intended cadence and overall visual style.
Related Terms
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