Canon MARK IV User Manual (en)

 Shooting Movies
About the ISO speed during manual exposure
The ISO speed can be set to [AUTO] (A) or within ISO 100-12800 in 
1/3-stop increments.
If the ISO speed is set to [AUTO] (A), the ISO speed will be set 
automatically within ISO 100-12800. (The [8C.Fn I -3: Set ISO 
speed range
] (p.208) setting will not take effect.) Movie shooting as 
in aperture-priority AE mode (fixed aperture, standard exposure) is 
then possible.
If [Highest ISO speed] is set to [H1] (ISO 25600), [H2] (ISO 51200), 
or [H3] (ISO 102400) in [8C.Fn I -3: Set ISO speed range], the 
ISO speed can be set manually within the expanded range up to the 
upper limit. Also, if the ISO speed range has been set to a narrower 
range than the default, you can set the ISO speed within the 
narrower range.
Even if [Lowest ISO speed] has been set to [L] (ISO 50) in [8C.Fn 
I -3: Set ISO speed range
], [L] cannot be selected when you set the 
ISO speed.
If [8C.Fn II -3: Highlight tone priority] (p.215) is set to [1: Enable], 
the settable ISO speed range will start from ISO 200.
Notes for autoexposure and manual exposure shooting
The camera cannot autofocus continuously like a camcorder.
During movie shooting, do not point the lens toward the sun. The sun’s 
heat can damage the camera’s internal components.
If <Q> is set and the ISO speed or aperture changes during movie 
shooting, the white balance may also change.
If you shoot a movie under fluorescent lighting, the movie image might 
If you use a lens whose aperture changes during zooming, zooming 
during movie shooting is not recommended since changes in the 
exposure may also be recorded.