Every video guide says to set the shutter to double the frame rate, so 1/50 at 25fps. I have tried faster and slower and the footage certainly looks different, but I do not know what I am supposed to be preserving.
Where does the rule come from and when should it be broken?
Accepted Answer
It comes from mechanical film cameras. A rotating disc with a 180 degree opening exposed the frame for half the time the shutter took to go round, so each frame carried motion blur covering half the frame interval.
Audiences learned that look over a century, so it reads as normal.
Faster shutter means less blur per frame, so motion becomes a series of sharp stills and looks stuttery. That is the Saving Private Ryan effect, used deliberately. Slower shutter smears motion and looks dreamlike or cheap depending on how far you push it.
So the rule preserves an expectation rather than a physical requirement. It is the default because it is invisible.
The common mistake is treating it as inviolable and then wrecking the exposure to obey it.
Outdoors in daylight at 1/50 you will be far overexposed even at a narrow aperture, and the usual fix is stopping down to f/16 where diffraction is already softening the image.
The correct fix is an ND filter, which is why they exist. If you do not have one, raising the shutter is a smaller sin than ruining the aperture. Consistency across a scene matters more than the exact figure anyway.
Worth knowing the number is an angle because the shutter really was a disc. Some cameras still let you set shutter angle instead of a fraction, which keeps the relationship correct automatically when you change frame rate.
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