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Shutter speed when shooting for slow-motion

Started Feb 5, 2022 | Questions thread
Sean Nelson
Sean Nelson Forum Pro • Posts: 16,109
Re: Shutter speed when shooting for slow-motion
1

nordic_shooter wrote:

If I shoot video at 60p, with the intention of playing it in it's native speed, according to the 180 deg rule I would use 1/120s shutter speed. If instead the intention is to play it at half speed (30fps), should I then shoot it at 1/60s ?

The purpose of using the "180 degree" shutter rule is to create motion blur that extends for half of the distance of movement between frames.

Imagine a dark night with a single small light panning across the frame - the motion blur means that the light would appear as a streak instead of a circle. If you were to superimpose all the frames, the streaks should form a nice "dotted line" appearance ( - - - - ) and the distance between each streak should be the same as the length of each streak.

In order to get this appearance at 60fps, you still need to expose each frame for half of the frame interval, which would be 1/120 of a second.   So the 180 degree rule applies to whatever frame rate you're shooting at, not what speed you play it back.

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