Canon EOS-1D X Mark II DSLR Camera (Body Only) - Manual (Page 164)

i : Setting the ISO Speed for Still Photos
164
As H1 (equivalent to ISO 102400), H2 (equivalent to ISO 204800), and
H3 (equivalent to ISO 409600) are expanded ISO speed settings, noise
(dots of light, banding, etc.) and irregular colors will be more noticeable,
and the resolution lower compared with the standard setting.
As L (equivalent to ISO 50) is an expanded ISO speed setting, the
dynamic range will be somewhat narrower compared with the standard
setting.
If [ z 2: Highlight tone priority ] is set to [ Enable ] (p.193), L (equivalent
to ISO 50), ISO 100/125/160, H1 (equivalent to ISO 102400), H2
(equivalent to ISO 204800), and H3 (equivalent to ISO 409600) cannot
be selected.
When shooting with a high ISO speed, high temperature, long exposure,
or multiple exposure, image noise (rough grain, dots of light, banding,
etc.) and irregular colors may become noticeable.
When shooting in conditions that produce an extreme amount of noise,
such as a combination of high ISO speed, high temperature, and long
exposure, images may not be recorded properly.
If you use a high ISO speed and flash to shoot a close subject,
overexposure may result.
If H1 (equivalent to ISO 102400) or higher (ISO 32000 or higher if the
camera’s internal temperature is low) has been set, the maximum
continuous shooting speed during high-speed continuous shooting will
be no faster than approx. 10.0 fps during viewfinder shooting or approx.
14.0 fps during Live View shooting. For details, see page 148.
Under [ z 2: ISO speed settings ], you can use [ Range for stills ] to
expand the settable ISO speed range from L (equivalent to ISO 50) to H1
(equivalent to ISO 102400), H2 (equivalent to ISO 204800), and H3
(equivalent to ISO 409600) (p.166).
Depending on the ISO speed setting, the shutter sound at the end of
shooting may differ.