Canon EOS-1D X Mark II DSLR Camera (Body Only) - Manual (Page 298)

k Shooting Movies
298
When the shooting mode is < f >, you can manually set the aperture
for movie shooting. The ISO speed and shutter speed will be set
automatically to suit the brightness and obtain the standard exposure.
1
Set the Live View shooting/Movie
shooting switch to <
k >.
2
Set the shooting mode to < f >.
Press the < W > button and turn
the < 6 > or < 5 > dial to select
< f >.
3
Set the desired aperture.
While looking at the LCD monitor,
turn the <
6 > dial.
4
Focus and shoot the movie.
The procedure is the same as steps 3
and 4 for “Autoexposure Shooting”
(p.296).
Aperture-priority AE
Aperture
Changing the aperture during movie shooting is not recommended since
variations in the exposure, due to the drive of the lens aperture, will be
recorded.