Canon EOS-1DX Instruction Manual page 331

Set shutter speed range
You can set the shutter speed range. In the <s> and <a> modes, you
can set the shutter speed manually within the range that you have set. In
the <d> and <f> modes, the shutter speed will be set automatically
within the range that you have set.
Highest speed
You can set it from 1/8000 sec. to 15 sec.
Lowest speed
You can set it from 30 sec. to 1/4000 sec.
Set aperture range
You can set the aperture range. In the <f> and <a> modes, you can set
the aperture manually within the range that you have set. In the <d> and
<s> modes, the aperture will be set automatically within the range that
you have set.
Min. aperture (Max. f/)
You can set it from f/91 to f/1.4.
Max. aperture (Min. f/)
You can set it from f/1.0 to f/64.
The settable aperture range will differ depending on the lens' maximum
and minimum apertures.
3 Custom Function Settings
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