180° rule & ND
Motion looks natural when the shutter is twice the frame rate. In bright light that shutter lets in too much, so you cut it back with an ND filter instead of speeding up.
Frame rate
Light
Aperture
ISO
Shutter (180°)1/50
ND filterND64
scene lightEV 15
your settingsEV 8.6
remove6.4 stops → ND64
Keeps the 180° shutter for natural motion blur instead of raising it in bright light.
The rule is shutter = 1/(2 × fps), snapped to a real speed:
24p → 1/50, 30p → 1/60, 60p → 1/125,
120p → 1/250. To find the filter, compare the scene's brightness
(in EV) to what your aperture, shutter, and ISO already expose; the
difference, in stops, is the ND you need.