Canon EOS-1D X Mark III Advanced User's Manual page 188

4.
Press the shutter button completely again.
The camera shoots.
When set to [Enable], the mirror is lowered after shooting.
When set to [Enable:Mirror down w/
after shooting. To lower the mirror, press <
Caution
Do not point the camera toward an intense light source, such as the sun or an
intense artificial light source. Doing so may damage the image sensor or the
camera's internal components.
In very bright light, such as at the beach or a ski slope on a sunny day, take the
picture promptly after mirror lockup is stabilized.
During mirror lockup, shooting function settings and menu operations are disabled.
Note
Single shooting drive mode is used when this function is enabled. When set to
[Enable:Mirror down w/
You can also use the self-timer with mirror lockup.
If approx. 30 sec. elapse after the mirror has locked up, it will go back down
automatically. Pressing the shutter button completely locks up the mirror again.
Use of a tripod and Remote Switch RS-80N3 or Timer Remote Controller TC-80N3
(both sold separately) is recommended (
], the camera shoots using the current drive mode.
).
188
], the mirror remains up
>.