Canon EOS-1D X Mark II DSLR Camera (Body Only) - Manual (Page 455)

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7 Custom Controls
For flash photography, pressing the button assigned to this function will
fire a preflash and record the required flash output (FE lock).
You can press < 0 > to change the ISO speed. Set while looking at the
top LCD panel or viewfinder.
You can set the ISO speed by holding down < 0 > and turning the
< 6 > dial. If this control is used with ISO Auto set, manual ISO speed
setting will take effect. It is not possible to revert to the ISO Auto setting.
If you use this function in the <
a > mode, you can adjust the exposure
with the ISO speed while maintaining the current shutter speed and
aperture value.
While the metering timer is active, you can set the ISO speed by turning
the <
5 > dial. The settable range is the same as with [ Set ISO speed
(hold btn,turn ) ].
While the metering timer is active, you can set the ISO speed by turning
the <
5 > dial. When this function is set, the functions of the < O > and
< i > buttons will be switched between the two. By pressing the
< i > button and turning the < 6 > dial, you can set the exposure
compensation or aperture value.
: FE lock
: Set ISO speed
: Set ISO speed (hold button, turn )
: Set ISO speed ( during metering)
Set ISO, O z g ( during metering)