Canon EOS-1D X Mark III Advanced User's Manual page 892

Expanded ISO speeds cannot be selected for still photo shooting.
Check the [ISO speed range] setting under [
Expanded ISO speeds are not available when [
[Enable] or [Enhanced].
Expanded ISO speeds are not available when [
[Enable].
Even if I set a decreased exposure compensation, the image comes out
bright.
Set [ : Auto Lighting Optimizer] to [Disable] (
[High] is set, even if you set a decreased exposure compensation or flash exposure
compensation, the image may come out bright.
I cannot set the exposure compensation when both manual exposure
and ISO Auto are set.
See M: Manual Exposure
Exposure compensation is not performed in flash photography.
Not all the lens aberration correction options are displayed.
Although [Chromatic aberr corr] and [Diffraction correction] are not displayed when
[Digital Lens Optimizer] is set to [Enable], both functions are applied in shooting, as
when set to [Enable].
During movie recording, [Digital Lens Optimizer] or [Distortion correction] will not be
displayed.
Images are not displayed after shooting in multiple-exposure shooting.
When [On:ContShtng] is set, images are not displayed for review after capture, and
image playback is not available (
Using flash in <
To provide suitable exposure for subjects and backgrounds, the shutter speed is
automatically reduced (slow-sync shooting) for shots under low light in night scenes or
with similar backgrounds. To prevent a slow shutter speed, set [Flash sync. speed in
Av mode] in [
(fixed)] ( ).
to set the exposure compensation.
).
> mode lowers the shutter speed.
: External Speedlite control] to [1/250-1/60sec. auto] or [1/250 sec.
: ISO speed settings].
: Highlight tone priority] is set to
: HDR shooting
). When [Low], [Standard], or
892
] is set to