Canon EOS-1D X Instruction Manual page 234

k Shooting Movies
Notes on Movie Shooting
The camera cannot autofocus continuously like a camcorder.
Autofocusing during movie shooting may momentarily throw the focus far
off or change the exposure.
When you autofocus during movie shooting under low-light conditions
using a USM lens, horizontal stripes (noise) may be recorded. Note that
with certain lenses equipped with the electronic focusing ring, similar
noise may be recorded even with manual focusing (MF).
Do not point the camera toward an intense light source, such as the sun
on a sunny day or an intense artificial light source. Doing so may
damage the image sensor or the camera's internal components.
Under [51: Record func+card/folder sel.], even if [Record func.] is set
to [Rec. to multiple] (p.120), the movie cannot be recorded to both Card
1 <f> and Card 2 <g>. If [Rec. separately] or [Rec. to multiple] is
set, the movie will be recorded to the card which is set for [Playback].
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 or LED lighting, the movie may
flicker.
Zooming the lens during movie shooting is not recommended. Zooming
the lens can cause changes in the exposure regardless of whether the
lens' maximum aperture changes or not. Exposure changes may be
recorded as a result.
Cautions for movie shooting are on pages 249 and 250.
If necessary, also read the Live View shooting cautions on pages
223 and 224.
Movie-related settings are under the [z4] and [z5] tabs (p.247).
A movie file is recorded each time you shoot a movie. If the file size
exceeds 4 GB, a new file will be created.
The movie image's field of view is approx. 100% (with movie recording
size set to [A]).
You can also focus the image by pressing the <p> button.
To focus during movie shooting, press the <p> button. You cannot
focus by pressing the shutter button.
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