Natural motion blur in video comes from a shutter speed of about 1/(2 × frame rate) — the 180° shutter rule. In daylight that usually needs an ND filter. Enter frame rate, shutter angle and the shutter speed your camera would use without a filter.
The result tells you the target shutter and the ND strength in stops and filter number.
How it works
t = (angle ÷ 360) ÷ fps. ND stops = log₂(t_target ÷ t_metered).
FAQ
Why 180 degrees?
It mimics film cameras' rotary shutters and gives motion blur that looks natural to viewers.
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