Canon EOS-1D X Mark III DSLR Camera (Body Only) - Manual (Page 178)

2.
Set the desired minimum shutter speed.
Automatically set
If you select [ Auto ], turn the < > dial to set the difference relative
to standard speed (toward Slower or Faster ), then press < >.
Manually set
If you select [ Manual ], turn the < > dial to select the shutter speed,
then press < >.
Caution
If a correct exposure cannot be obtained with the maximum ISO speed limit set
with [
Auto range ], a shutter speed slower than the [ Min. shutter spd. ] will be set
to obtain the standard exposure.
This function will not be applied to flash photography.
Note
When [ Auto(Standard) ] is set, the minimum shutter speed will be the reciprocal of
the lens focal length. A single step from [ Slower ] to [ Faster ] is equivalent to a
single stop of the shutter speed.
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