Canon EOS 5DS Instruction Manual page 480

Troubleshooting Guide
The manually set ISO speed changes when
switching to movie shooting.
If you shoot a movie with manual exposure set to L (equivalent to ISO
50), the ISO speed setting will switch to ISO 100. Even if you switch
back to still photo shooting, the ISO speed will not revert to L.
The exposure changes during movie shooting.
If you change the shutter speed or aperture during movie shooting, the
changes in the exposure may be recorded.
Zooming the lens during movie shooting can cause changes in the
exposure regardless of whether the lens's maximum aperture changes
or not. The changes in the exposure may be recorded as a result.
The image flickers or horizontal stripes appear
during movie shooting.
Flickering, horizontal stripes (noise), or irregular exposures can be
caused by fluorescent lighting, LED lighting, or other light sources
during movie shooting. Also, changes in the exposure (brightness) or
color tone may be recorded. In the <a> or <s> mode, a slow
shutter speed may reduce the problem. The problem may be more
noticeable in time-lapse movie shooting.
The subject looks distorted during movie shooting.
If you move the camera to the left or right (panning) or shoot a moving
subject, the image may look distorted. The problem may be more
noticeable in time-lapse movie shooting.
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